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Tree pathology and Tree Assessment

Module 3

Tree pathology (diagnosis and plant disorders) and Tree Assessment

Table of Contents

1. Tree Pathology

Pathology is a science that deals with the study of diseases, i.e. changes in cells, tissues and organs that occur during disease. Plant pathology is an integral part of all horticulture systems (conventional, integrated and ecological). For successful protection of plants, it is necessary to know the technology of growing plants, but also the pathogens that harm them as well as ways of their suppression. The task of phytopathology is to prevent infection, i.e. the onset of disease. Diseases and pests on trees can be caused by viruses, fungi, bacteria and insects. It is necessary to determine the causes of plant diseases and find out more about the cause of the disease. The task of phytopathology, in addition to the above mentioned, is to know how host resistance changes under the influence of surrounding factors and humans, how the parasitic ability changes under the influence of internal and external factors, and to learn how to use all available plant protection measures.

Plants are subject to various harmful influences. They can be external and internal. External influences are climate conditions, anthropogenic influences, ecological influences, etc., while internal conditions are those originating from the plant community itself. Plant diseases can be caused by various pathogens – of abiotic or biotic origin. Diseases of abiotic origin are non-parasitic diseases, and they are most often caused by climate factors and edaphic factors such as excess or lack of minerals in the soil, acidity, water-air regime of the soil, excess air and water pollution.

Figure 1. A quick guide to some features of tree diseases.
Source: Pest Forest leaflet (2001) Introduction to Forest Diseases. (Accessed 18. 1. 2024)

Parasitic diseases are caused by living organisms, i.e. microorganisms that are infectious and can be transmitted from plant to plant. The most important diseases of ornamental and forest trees are mycoses.

Parasitic diseases:

  • Mycoses (caused by fungi)
  • Bacteriosis (caused by bacteria)
  • Virosis (caused by viruses)
  • Mycoplasmosis (caused by organisms similar to mycoplasmas – MLO)

Plant pests – belong to various groups of animals, the most important of which are: insects, mites, nematodes, snails, birds and mammals. The abundance of one species depends on the temperature of the environment, air humidity, available food and natural enemies.

Types of pests

Among the more important pests, we include the following species: 

  • Butterflies do no harm, their caterpillars do the most damage.
  • Beetles as well as their larvae – feed by biting plant parts.
  • Hymenoptera – their larvae cause damage by biting various wasps.
  • Diptera – adults do not cause damage, the larvae live in the fruits they feed on. 
  • Aphids and scale insects – they cause damage by sucking plant juices in all stages of their growth, they excrete honeydew.
  • Mites – they differ from insects because they have four pairs of legs. 
  • Nematodes – live in the soil and attack the roots and create growths that destroy the main root. Some species can live in the aerial parts of plants.
  • Snails – the biggest damage is caused by slugs, they feed on leaves and soft parts of the plant, they leave traces of slime.
  • Rodents-cause damage by biting the bark and parts of the roots.
  • Game – they damage young trees, gnawing the bark and feed on the leaves.

1.1. Biodiversity – Importance and Protection

Biodiversity implies the diversity of genes, species, communities of species, ecosystems, i.e. diversity on Earth as a complete ecosystem. Biodiversity is a source of genetic material that enables the development of new and improved varieties of plants. Diversity of species is considered to be the best indicator of biodiversity. Genetic differences within the same species are considered morphological and physiological differences. Biological diversity reduces the risk of negative impacts from adverse weather conditions and protects against disease and pest attacks. 

Trees and shrubs enable the population of beneficial insects and other fauna to increase. Apart from the habitat, every organism is affected by all the living things that surround it. 

These mutual influences of living beings are biotic factors, in which we can also include human influence, the so-called anthropogenic factor. Individuals of the same species in the population are connected by a series of relationships, primarily through reproduction. Populations are constantly changing, increasing or decreasing in number. They increase by birth, i.e. by the creation of new individuals. The number is reduced by mortality or the so-called. mortality. In addition to reproductive relationships, there are also a number of others, such as competition for living space, for food, for a sexual partner, etc. Such relationships are called INTRASPECIES RELATIONS, i.e. relationships within a species. Relationships between different species are called INTERSPECIES RELATIONS.

Urban green areas enable ecosystem services – support biological diversity, maintenance of favorable microclimatic conditions, infiltration of water into the soil, sequestration of carbon dioxide, visual and aesthetic quality, recreation and social capital. Vegetation in cities reduces noise. The loss of trees, green areas and biological diversity has a negative effect on the inhabitants of cities, because the microclimatic conditions for life are disturbed, the soil dries up, air quality and groundwater levels decrease, people’s health is threatened due to the appearance of pests and diseases. In addition to planting trees and expanding green areas, urban forests represent perhaps the most ambitious form of returning nature to cities. They provide multiple benefits to the urban population, and in addition to influencing the quality of life and providing a place for rest and recreation, they help create a pleasant microclimate and lower the air temperature in overheated cities, increase carbon dioxide and purify the air, promote biological diversity, and thus have a positive effect on people’s physical and mental health.

1.2. Tree Stress

Plant stress is the result of the influence of various substances that interfere with the plant’s metabolism, or it is the result of unfavorable living conditions. The main cause of stress can be abiotic or biotic. Depending on the duration, stress can be long-term or short-term. Stress is most often the result of a combination of different negative influences on the plant itself. There are several types of stress with regard to the number of causes of it – individual and combined stress. Individual stress is manifested as a consequence of one factor that has a negative effect on the plant, on its growth and development. Combined stress occurs as a result of the cumulative action of several factors, for example summer drought together with high temperatures (abiotic factors) or the simultaneous attack of several harmful organisms (biotic factors).

1.2.1 Abiotic Disorders

Abiotic disorders are disorders and damage that occur under the influence of unfavorable climatic and pedological factors such as: 

1. Temperature

  • High temperature – 46-52ᵒC drying of plants and plant parts, bark inflammation, the higher the water content, the more sensitive the plant is to high temperatures. Protein denaturation above 50 degrees. 
Figure 2: Bark damage due to overheating.
Source: Butin H. & Brand T. (2017). Bark damage due to overheating. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.23). Ulmer Verlag
Figure 3: Burn damage caused by exposure to extreme heat.
Source: Butin H. & Brand T. (2017). Burn damage caused by exposure to extreme heat. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.247). Ulmer Verlag
  • Low temperature – damage to plant parts from frost (late spring and early autumn, greater damage to plants full of water). Low temperatures lead to the formation of ice crystals in the cells and intercellular spaces, and as a result the cells tear and dehydration of the protoplasm occurs.
Figure 4: Bronze coloring in winter, Buxus.
Source: Butin H. & Brand T. (2017). Bronze coloring in winter, Buxus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.50). Ulmer Verlag
Figure 5: Frost dryness.
Source: Butin H. & Brand T. (2017). Frost dryness. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.50). Ulmer Verlag

2. Lack of moisture in the soil

Figure 6: Wilting damage due to lack of water.
Source: Butin H. & Brand T. (2017). Wilting damage. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.193). Ulmer Verlag

3. Too much moisture in the soil – it prevents the normal absorption of oxygen through the roots, so the plants die. Often there is hypertrophy of the root lenticels, which can be seen in the form of whitish formations on the root itself.

Figure 7: Bark damage caused by weather extremes.
Source: Butin H. & Brand T. (2017). Bark damage caused by weather extremes. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.257). Ulmer Verlag

4. Insufficient light – leads to plant etiolation, i.e. elongated growth, whereby the plants are lighter in color. Affected plants are not resistant and easily succumb to various infections. A too dense planting system can result in a lack of light, which causes the plants to elongate.

5. Too much light – the plants take on a washed-out appearance and get burned.

Figure 8: Extensive yellowing throughout strong sunlight.
Source: Butin H. & Brand T. (2017). Extensive yellowing throughout strong sunlight. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.56). Ulmer Verlag

6. lack of oxygen in the soil,

7. Polluted air: 

  • Sulfur dioxide (SO2): is produced in thermal power plants by burning coal, smelting copper, lead, zinc and nickel ores, at high concentrations chlorosis occurs,
  • Hydrogen fluoride (HF) and silicon tetrafluoride (SiF4): are produced in aluminum smelters, during the production of phosphorus fertilizers, iron processing and steel production. High concentration: peripheral necrosis and chlorosis of leaves and neadles
  • Nitrogen oxides (NO2, NO3): are produced in internal combustion engines, during oil refining, burning of natural gas and fuel oil. Necrotic spots develop on young conifers at elevated concentrations.

8. Too much salt in the soil – a problem present in urban areas, roads are sprinkled with salts (NaCl, CaCl2, MgCl2). Excessive amounts of salt for sprinkling in the soil are washed into deeper layers and affect reverse osmosis (water from the plant goes through the root hairs into the soil, which causes water problems and permanent damage to trees in the form of weaker leaf growth, drying of the leaves and the entire tree. According to their sensitivity to the salt effect, forest species are divided into 4 groups:

  • very sensitive (spruce, Douglas fir, horse chestnut)
  • sensitive (maple, beech, cherry, linden)
  • slightly sensitive (birch, alder, ash, elm, pines, acacia)
  • insensitive (yew, oak, white poplar, plane, willow)
Figure 9: Leaf discoloration due to chloride poisoning.
Source: Butin H. & Brand T. (2017). Leaf discoloration due to chloride poisoning. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.29). Ulmer Verlag

9. High concentration of heavy metals in the soil (plants that grow on soil contaminated with heavy metals experience a reduced level of growth as a result of changes in physiological and biochemical processes. This reduces the annual yield of leaf mass on trees, which leads to the gradual death of trees and changes in the ecosystem).

10. Lack of nutrients in the soil – macronutrients – nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). Micronutrients – iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), boron (B), molybdenum (Mo) and chlorine (Cl). The lack of these elements leads to the appearance of non-specific symptoms that can be confused with symptoms caused by fungi. A lack of nitrogen leads to a chlorotic appearance of plants, slowed growth, falling leaves, while an excess of nitrogen leads to lush growth, a dark green color of plants, prolongs the growing season, the formation of a thinner epidermis of the leaves, which affects the stronger development of the causative agent of the disease. Correction is carried out by fertilizing after pedological analysis of the soil for nutrients. Phosphorus deficiency is manifested by the reddish or purple color of the leaves, which are smaller and stand upright. Root development is weaker, and the plants take on a rigid, stiff appearance. Excess phosphorus is very rare in nature, but if it occurs, it causes phytotoxicity. A lack of potassium can be seen through chlorosis and necrosis of the edges of the leaves, which can spread to the entire plant. The leaves take on a reddish colour, buds form more poorly, flowers fall off and the development of the root system is weaker. An excess of potassium is very rare in nature, but it is known that a good supply of potassium increases the resistance of plants. Calcium deficiency manifests itself in chlorosis and dying out of meristems, sometimes even whole plants. Iron deficiency is manifested as chlorosis, it occurs especially on alkaline soils and first on the youngest leaves. Zinc deficiency manifests itself through chlorosis and necrosis with leaf shedding (defoliation) and formation of small leaves. The lack of boron manifests itself through the drying of twigs and the creation of “witches’ broom”.

Figure 10: Leaf discoloration due to iron manganese deficiency.
Source: Butin H. & Brand T. (2017). Leaf discoloration due to iron manganese deficiency. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.179). Ulmer Verlag
Figure 11: Leaf discoloration due to iron manganese deficiency, Rhododendron.
Source: Butin H. & Brand T. (2017). Leaf discoloration due to iron manganese deficiency, Rhododendron. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.179). Ulmer Verlag
Figure 12: Leaf discoloration due to magnesium deficiency.
Source: Butin H. & Brand T. (2017). Leaf discoloration due to magnesium deficiency. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.82). Ulmer Verlag
Figure 13: Needle yellowing due to iron-manganese deficiency.
Source: Butin H. & Brand T. (2017). Needle yellowing due to iron-Manganese deficiency. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.135). Ulmer Verlag

11. Mechanical damage – by wind, snow, ice, hail, lightning and machinery.

  • Wind: mechanical (windbreaks and tree bending) and drying (increased evaporation of water). 
  • Snow: snow breaking and snow bending. Snowfalls are common on fir trees at the sites of tumors (caused by the fungus Melampsorella caryophyllacearum). In the natural habitats of fir and spruce, the fungus Heterobasidion annosum causes rotting of the roots of trees that are easily laid down. Snow directly affects the appearance of pathogenic fungi that develop on snow-covered areas Phacidium infestans (“snow fungus”). Herpotrichia juniperi (the cause of black cobwebs in conifers – young spruce, mountain pine and pine).
Figure 14: Bark damage caused by mechanical damage.
Source: Butin H. & Brand T. (2017). Bark damage caused by mechanical damage. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.257). Ulmer Verlag

12. Climate change

13. Acid rain – formed by the reaction of SO2 and NO2 with water, which leads to the formation of sulfuric (H2SO4) and nitric acid (HNO3), the acidity of the rain is pH 5.3; acid precipitation in the rain: pH≤2.5, consequences: by reducing the pH of the soil, the concentration of aluminum increases, the death of fine roots and mycorrhizae. Symptoms of the disease are seen as necrosis of lenticels and leaves, fading of the interveinal space on the leaves due to the breakdown of chloroplasts.

Figure 15: Acid rain.
Source: Arboriculture blog (2016) The Effect Acid Rain on Tree Populations. (Accessed 18.1.2024)

14. Phytotoxicity – injuries are caused by the inadequate application of plant protection agents, which manifests itself in the form of various injuries and burns.

Abiotic factors lead to a decrease in the vitality of trees, which then become sensitive to biotic agents.

Figure 16: Branch dieback on firethorn hedges through abiotic causes.
Source: Butin H. & Brand T (2017). Branch dieback on firethorn hedges through abiotic causes. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.175). Ulmer Verlag

1.2.2. Biotic Disorders

Biotic disorders are caused by various living organisms that live in certain conditions on plants. This group includes: fungi, bacteria, viruses and semi-parasites.

Parasites are heterotrophic organisms that feed at the expense of other living beings. Pathogenic organisms infect other living beings. In order for the pathogen to infect, there must be compatibility between it and the host.

FUNGI

Vegetative body of fungi – thallus or mycelium is composed of unicellular and reticulated multicellular hyphae.

Reproduction is sexual or asexual (spores are created as a product of both reproductions):

  • Asexual spores (conidia and pycnidia) are often located on supports
  • Sexual spores are created in small fruiting bodies (cleistothecia, perithecia and apothecia) or in large fruiting bodies (mushroom, carpophores).
Figure 17: Disease causing spores I.
Source: Butin H. & Brand T (2017). Disease causing spores I. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.271). Ulmer Verlag
Figure 18: Disease causing spores II.
Source: Butin H. & Brand T (2017). Disease causing spores II. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.272). Ulmer Verlag
Figure 19: Disease causing spores III.
Source: Butin H. & Brand T (2017). Disease causing spores III. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.273). Ulmer Verlag

BACTERIA

Diseases caused by bacteria are called bacterioses. More than 300 species and varieties of phytopathogenic bacteria are known today. Bacteria parasitize more than a thousand plant species. The first bacteria discovered is Erwinia amylovora, which causes great damage to fruit trees. 

Bacteria reproduce vegetatively, most often by division, rarely by budding. They are facultative parasites. They penetrate plants through natural openings, stomata, lenticels, hydathodes or through injuries caused by hail, wind, snow or biotic factors (insects, nematodes, humans). 

The optimal conditions for the development of bacteria are pH 6,2 – 6,8, temperature 25 – 30ᵒC. They favor conditions of increased humidity, and there is almost no infection without a drop of water. Bacteria lose their vitality under the influence of direct sunlight. 

The most common carriers of bacteria are humans, animals and water.

The most important genera of phytopathogenic bacteria are  Agrobacterium,  Erwinia,  Pseudomonas,  Xanthomonas and Streptomyces.

Figure 20: Agrobacterium.
Source: Wikipedia (no date) Agrobacterium.
(Accessed 19.1.2024)
Figure 21: Erwinia.
Source: Wikipedia (no date) Erwinia.
(Accessed on 18.1.2024)
Figure 22: Pseudomonas.
Source: Wikipedia (no date) Pseudomonas.
(Accessed 19.1.2024)
Figure 23: Xsanthomonas.
Source: Arboriculture blog (2016) Xanthomonas.
(Accessed on 18.1.2024)

Bacteria spread intracellularly, degrading the central lamellae. They appear on the surface of plants in the form of bacterial exudate (drops or mucus). Symptoms of bacteriosis:

  • Wet rot – develops on tissues rich in water and nutrients (Erwinia)
  • Spotting and necrosis – this is the most common type of symptom in bacteriosis, the spots are initially watery and transparent, later turn brown, and due to the rupture of dead tissue, they get the appearance of a scab with a brown edge (Xanthomonas, Pseudomonas)
  • Burning – the attacked organs or part of them turn brown or black and dry out (Erwinia)
  • Withering – wilting of individual parts or entire plants (Erwinia, Pseudomonas)
  • Various growths and tumors – under the influence of bacteria, hypertrophy and hyperplasia occur, resulting in growths, swellings and tumorous growths (Agrobacterium).

VIRUSES

They cause viral infections, and the science that deals with the study of viruses is called virology. Basic characteristics of the virus:

  1. obligate parasites
  2. submicroscopic sizes – pass through the bacterial filter
  3. multiply in a living cell of the appropriate host
  4. without own enzyme system or metabolism
  5. resistant to antibiotics

The virus enters the plant through injuries, i.e. wounds. The plants are most often systemically infected, which is manifested as chlorosis. 

Viruses can be transmitted and spread mechanically through:

  • sap from a diseased plant to a healthy plant, 
  • grafting, 
  • cuttings, 
  • shoots, 
  • vegetative organs, 
  • insects, nematodes, fungi, parasitic flowering plants (Cuscuta sp.), 
  • seeds, 
  • soil

Protection measures are:

  • destruction of the infection hotspot, 
  • destruction of virus carriers (vectors), 
  • cultivation of resistant varieties and hybrids, 
  • therapy of diseased plants – thermotherapy, 
  • spatially isolate species that can be attacked the same types of viruses
Figure 24: Yellow spotting due to viral infection.
Source: Butin H. & Brand T (2017). Yellow spotting due to viral infection. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.120). Ulmer Verlag

SOIL PATHOGENS

Some economically important plant diseases are caused by pathogens present in soil. Many of these organisms have developed specialized survival structures such as hardened mycelia (sclerotia) or thick-walled spores (chlamydospores or oospores). These specialized structures help them survive in harsh soil conditions. Others remain as saprophytes, earning their living by decomposing dead plant tissues. Many of these so-called soil-borne pathogens persist in the soil for long periods of time, from one growing season to another, even if environmental conditions do not support disease development. When optimal conditions appear (the right moisture, temperature and presence of a host plant), these pathogen structures in the soil often serve as a source of inoculum for disease development. The most important fungal pathogens in the soil: Fusarium, Macrophomina, Phytophthora, Pythium, Rhizoctonia, Sclerotinia, Sclerotium, Verticillium.

Fusarium species cause root rot, wilting and yellowing of many young plants in the nursery.

Macrophomina phaeseolina is the causative agent of charcoal rot disease. This fungus has a wide range of hosts, more than 500 species. It causes a range of symptoms, including seedling rot, rot and wilting of roots and stems. Hot weather favors the development of diseases.

The genus Phytophthora includes several economically important plant pathogens that cause blight, canker, and rot on a variety of plant species. Plants in nurseries get sick.

Pythium species like its relatives, Phytophthora spp., are water-loving organisms. It destroys seedlings in the nursery. Symptoms include stunting, wilting (dying) and crown lesions. There are often no fine roots, while the main roots are brown or black.

Rhizoctonia solani is a common pathogen in the soil that causes wetting, rotting of roots and stems of various plant species.

Sclerotinia species are the causative agents of stem rot and soft rot of many ornamental species.

Sclerotium species cause root rot, stem canker, root rot, crown rot, on a variety of plants, including vegetables, legumes, and grains. Diseases caused by these fungi are often called wilt.

Verticillium dahliae, the causative agent of Verticillium wilt, is a true soil-borne pathogen that can survive in the soil for up to 15 years as a microsclerotia. Another species of Verticillium, V. albo-atrum also causes wilting, but differs from V. dahliae in that it does not produce sclerotia. Verticillium species attack more than 200 plant species including vegetables, flowers, strawberries, fruit trees and forest trees.

Figure 25: Sclerotinia sclerotiorum, Forsythia.
Source: Butin H. & Brand T (2017). Sclerotinia sclerotiorum. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.91). Ulmer Verlag

1.4. Exotic Pathogens

Disease agents and pests from other climates, quarantine harmful organisms that appear in the EU: Fusarium circinatum, Ceratocystis platani, Bursaphelenchus xylophilus, Trioza erytreae, Popillia japonica, Aromia bungii, Anoplophora chinensis.

  • Fusarium is a fungal plant pathogen that causes bark cancer disease. Fusarium  infects pine branches and thus causes bark cancer. The most common hosts of the pathogen are Pinus eliotti, Pinus tadea, Pinus radiata and Pinus patula.
Figure 26: Fusarium circinatum, Pinus.
Source: Wikipedia (no date) Fusarium circinatum.
(Accessed on 18.1.2024)
  • Ceratocystis platani – a fungus that causes a disease on plane trees of the genus Platanus, mainly in North America and Southern Europe.
Figure 27: Ceratocystis platani.
Source: Wikipedia (no date) Ceratocystis platani.
(Accessed on 18.1.2024)
  • Bursaphelenchus xylophilus – known as pine tree nematode or pine wilt nematode (PWN), is a species of nematode that infects trees in the genus Pinus.
Figure 28: Bursaphelenchus xylophilus.
Source: StetniciHr (2017) Borova nematoda.
(Accessed 19.1.2024)
  • Triosa erytreae – African citrus tree. A semi-winged bug from the family Triozidae, which sucks sap. It is an important citrus pest, being one of only two known vectors of a serious citrus disease (citrus greening disease).
Figure 29: Trioza erytreae.
Source: Wikipedia (no date) Trioza erytreae.
(Accessed 19.1.2024)
  • Popilia japonica – is a known pest of approximately 300 plant species, including rose bushes, grapevines, hops, hemp, myrtles, birches, lindens, and others. Adult Japanese borers damage plants by skeletonizing the leaves (i.e., consuming only the material between the veins of the leaf), as well as by feeding on the plant’s fruits. Underground larvae feed on grass roots.
Figure 30: Popillia japonica.
Source: Wikipedia (no date) Popillia japonica.
(Accessed 19.1.2024)
  • Aromia bungii – The larvae bore holes in the wood and thicker branches, which causes the tree to weaken and lose fruit. Hosts are Prunus sp. (especially peach and apricot), Prunus domestica, Prunus avium, Azadirachta indica (Meliaceae), Bambusa textilis (Poaceae), Diospyros virginiana (Ebenaceae), Olea europea, Populus alba (Salicaceae), Pterocarya stenoptera (Juglandaceae), Punica granatum ( pomegranate – Lythraceae), Schima superba (Theaceae)
Figure 31: Aromia bungii.
Source: StetniciHr (2017) Aromia bungii.
(Accessed 18.1.2024)
  • Anoplophora chinensis – Asian citrus long-horned beetle belongs to the group of polyphagous harmful organisms and according to the data known so far, it occurs on species from the following genera: Acer, Aesculus, Alnus, Betula, Carpinus, Corylus, Cotoneaster, Crataegus, Fagus, Ficus, Fraxinus, Malus, Morus, Platanus , Populus, Prunus, Pyrus, Quercus, Rosa, Salix and Ulmus.
Figure 32: Anoplophora chinensis.
Source: Enthomology today (no date) Citrus longhorned beetle (Anopophora chinesis).
(Accessed 18.1.2024)

Quarantine harmful organisms that do not occur in the EU, but are likely to occur: Genus Acleris, Agrilus anxius, Agrilus planipennis, Aleurocanthus woglumi, Anoplophora glabripennis, Anthonomus quadrigibbus, Aschistonyx eppoi, Bemisia tabaci, Dendrolimus sibiricus, etc. 

Source: Priručnik za specijalizirane subjekte (no date). Karantenski štetni organizmi Europske Unije. Centar za zaštitu bilja. (Accessed 18.1.2024)

1.5. Pathology Analysis

Pathogens can be transmitted and spread in the following ways – infected plant material, wind, water, soil, animals, human carriers.

Pathogenesis is the origin and course of a disease.

Infection is the penetration of the parasite into the host. The infection time is of different duration for individual diseases.

Incubation – the time from infection to the appearance of the first symptoms is different and depends on a number of factors, usually lasting from 7 to 14 days, with some viruses 1 to 2 days.

Fructification – the period of time from the establishment of contact between the parasite and host cells (infection) until the appearance of the reproductive organs of that parasite. On average, it lasts 1 to 2 days longer than incubation.

Figure 33: Life cycle of the gram negative bacterium Xanthomonas campestris.
Source: Wikipedia (no date) Plant pathology Black root lifecycle.
(accessed 19.1.2024.)

NUMERICAL THRESHOLD OF INFECTION 

In some fungi, infection can occur if only one spore is present (if the host is susceptible). In the case of other fungi and bacteria, the infection cannot be achieved by one spore or bacteria, but by more than one. In the case of tolerant cultivars, a significantly higher number of parasites is needed for an infection to occur. The density of spores and parasites on the host plant is the strength of the infection, which can be minimal, optimal and maximal. The minimum density of disease-causing spores, necessary for the onset of disease, is called the NUMERICAL THRESHOLD OF INFECTION. For infection to occur, there must be an appropriate attraction or tropism between host and parasite. A spore of a causative agent cannot fall on any plant and cause the appearance of a disease. Aggressiveness is the ability of a parasite to attack a plant, carry out an infection, feed and reproduce from the plant cell. Pathogenicity is the ability of the parasite to cause disease in the host.

PRINCIPLES OF PLANT RESISTANCE

Living beings have a natural resistance to some diseases, which is conditioned genetically. Acquired resistance occurs after recovery and is not hereditary.

Resistance can be:

  • Passive – includes morphological, histological, chemical and other properties and conditions of the host, which reduce the probability of infection and spread of the parasite.
  • Active – the ability of the organism to stop or eliminate the parasite after infection with a set of cytoplasmic defense reactions. It is activated if the factors of passive resistance do not fulfill their task. Defense reactions of active resistance can be:
  • antiparasitic – directed towards the parasite, their aim is to weaken or destroy the parasite.
  • antitoxic – they are aimed at binding or breaking down the toxin produced by the parasite.
  • Induced defense reactions and pre-immunity – the reaction of plants is directed against their own sensitivity, not against parasites.

Conclusion

In conclusion, this comprehensive overview of plant pathology delves into the multifaceted world of plant stress, disorders, and the various biotic and abiotic factors that impact the health and vitality of plants. Stress, whether stemming from single or combined factors, has the potential to greatly affect plant growth and development, making it essential to understand and mitigate these influences. The field of plant pathology plays a pivotal role in understanding and safeguarding the health of plants in various horticulture systems. It is not merely about identifying diseases, but also about comprehending the diverse factors that influence plant health, both internal and external.

Abiotic disorders, including extreme temperatures, moisture levels, light conditions, and soil factors, are highlighted as major culprits in plant health issues. These disorders can lead to symptoms like wilting, rotting, discoloration, and a host of other challenges, ultimately reducing the vitality of trees and rendering them susceptible to biotic agents. Biotic disorders, on the other hand, are predominantly caused by living organisms like fungi, bacteria, and viruses. These pathogens can manifest in various ways, including wet rot, spotting, burning, and wilting, depending on the specific type of organism responsible. Understanding the characteristics and behaviors of these pathogens is crucial for disease management. 

Understanding biodiversity is crucial in this context, as it fosters resilience in plant populations and ecosystems. Biodiversity ensures genetic diversity, which, in turn, aids in the development of robust plant varieties. Moreover, the complex web of interactions among species, both within and between species, underscores the interconnectedness of all living organisms. This intricate tapestry of life, influenced by both natural and anthropogenic factors, highlights the need for a comprehensive understanding of the ecosystems in which plants thrive. Lastly, the concept of plant resistance is introduced, emphasizing the importance of understanding both passive and active resistance mechanisms in plants. These mechanisms play a pivotal role in mitigating the impact of pathogens and diseases, and can be crucial for disease management strategies.

2. Tree assessment

2.1. Tree inspection

Regular tree inspection provides an opportunity to recognize early signs of disease or infestation. Tree inspections help maintain the aesthetic appeal of the landscape by identifying and addressing problems that may affect the visual appeal of trees. In general, regular tree inspections are key to ensuring the well-being and longevity of trees, as well as preserving the beauty of the natural environment.

The methods used to inspect trees and determine the cause of damage are: 

  • detailed visual ASSESSMENT of the tree and the environment around the tree
  • vitality assessment 
  • sampling and analysis of diseased parts, attacked by pest or stress

2.2. Analysis

By carefully inspecting the leaves, bark, branches and the overall health of the tree, any growth anomalies, discoloration or the presence of pests can be observed. This early detection allows quick action to be taken, such as applying appropriate treatments or removing the diseased tree to prevent the spread of the disease or infection to other trees in the area. Recognizing signs of disease or infestation during regular tree inspections helps maintain the overall health and vitality of the tree population, ensuring their longevity. 

VTA or Visual Tree Assessment in arboriculture is a systematic method for evaluating the health and structural integrity of trees. VTA is an important part of tree care and risk assessment, and it is commonly used in urban forestry and tree management programs.

Steps for conducting a VTA:

Preparation: Before you start, make sure you have the necessary tools and equipment, such as binoculars, a clipboard, a checklist or form for documentation, and personal protective gear (if needed).

Identification: Identify the tree species you are assessing, as different species may have varying characteristics and requirements.

Overall Inspection:

  • Crown: Start by examining the tree’s crown. Look for signs of dead or declining branches, missing foliage, and abnormal growth patterns.
  • Trunk: Inspect the trunk for wounds, cracks, decay, or signs of pest infestations. Pay attention to any swelling or abnormalities.
  • Root Zone: If possible, assess the root zone for issues like girdling roots, soil compaction, or other stress factors that may affect the tree’s health.

Branch Structure: Assess the branches for dead or dying limbs, weak attachments, or limbs with a heavy load of foliage or fruit. Look for any branches that are crossing or rubbing against each other.

Health Evaluation: Check for signs of disease, such as cankers, leaf discoloration, or fungal growth. Look for signs of insect infestations, including exit holes, sawdust, or the presence of pests.

Assess Environmental Factors: Consider environmental conditions, such as soil quality, moisture levels, and the tree’s proximity to structures, utilities, and high-traffic areas.

Safety and Risk Assessment: Evaluate the tree’s potential hazards, such as dead branches that could fall, leaning trunks, or roots that might cause tripping hazards. Determine the tree’s risk level and the likelihood of failure, taking into account its location and surrounding structures.

Documentation: Record your observations on a VTA checklist or form, noting the tree’s condition, health, and any identified issues. Take photos or sketch diagrams to provide a visual record of the tree’s condition.

Based on your assessment, provide recommendations for any necessary actions. These may include pruning, removal, pest control, or other maintenance measures. If the tree requires ongoing monitoring or management, schedule follow-up assessments to track changes in its condition.

Visual Tree Assessment is a non-invasive method that relies on the expertise of trained professionals to visually inspect and evaluate trees. It is an essential tool for managing tree populations in urban areas, parks, and other settings, helping to ensure the safety and longevity of trees while maintaining a balance with human infrastructure and safety.

2.2.1. Soil analysis

Soil analysis is the one of the best ways to ensure that the trees will remain healthy. Testing the soil in an area where trees are planted can help identify potential threats to their health. By testing soil samples from around the tree, it’s possible to identify diseases and pests that may be present in the root system. Similarly, soil testing can indicate contamination in the soil, such as runoff from chemicals or an excess of fertilizer. Both can be detrimental to tree health, and soil testing can help homeowners act quickly when signs of these problems arise. Soil analysis can be done before planting plants to check for two things – soil pH and nutrients in the soil. If soil pH is too low or too high, plants are unable to take in some of the nutrients provided to them in the soil. The best time to test your soil is a couple of weeks before you plan to plant. Test in early fall, for example, to understand the state of your soil before late fall or early spring planting. The essential macronutrients tested are calcium, magnesium, nitrogen, phosphorus, potassium, and sulfur.

Figure 34: How to take a soil sample.
Source: Blue-fifty (2018) How to take a soil sample

2.2.2. Biological analysis

Biological analysis of trees, often referred to as tree biology or arboriculture, is a field of study that focuses on understanding the various biological aspects and processes related to trees. This discipline involves the study of tree anatomy, physiology, genetics, and ecology. Here are some key components of biological analysis of trees:

Tree Anatomy: This aspect of tree biology involves the study of the internal and external structure of trees. It includes understanding the different parts of a tree, such as roots, stems, leaves, and branches, and how they function. Arborists and researchers examine tree rings, bark, wood, and other structures to learn about a tree’s growth and history.

Tree Physiology: Tree physiology deals with the functioning of trees, including processes like photosynthesis, transpiration, and nutrient uptake. It explores how trees absorb and transport water and nutrients, exchange gasses with the environment, and respond to environmental factors like light, temperature, and moisture.

Genetics: Genetic analysis of trees involves studying the hereditary factors that influence tree traits, growth patterns, and disease resistance. This is particularly important in the context of breeding programs to develop tree varieties with desirable characteristics.

Ecology: Understanding the ecological role of trees in ecosystems is a crucial part of tree biology. It examines how trees interact with other organisms, their role in nutrient cycling, their influence on microclimates, and their impact on biodiversity.

Disease and Pest Management: Biological analysis also includes the study of tree diseases and pests. This involves identifying pathogens and pests that affect trees, understanding their life cycles, and developing strategies to manage and mitigate these threats.

Root Structure and Soil Interaction: The roots of trees play a vital role in anchoring the tree, absorbing water and nutrients, and interacting with the surrounding soil. Tree biology includes the study of root systems and how they interact with the soil environment.

Environmental Impact and Climate Change: As trees are key components of ecosystems and influence local climates, biological analysis also examines the broader environmental impact of trees. Researchers investigate how trees can mitigate climate change by sequestering carbon dioxide and their sensitivity to changing climate conditions.

Biological analysis of trees is essential for proper tree care, conservation, and management. It helps arborists, ecologists, and researchers make informed decisions about tree planting, maintenance, and protection, especially in the context of preserving green spaces, urban forestry, and sustainable forest management.

Conducting a biological analysis of a tree involves a systematic examination of the tree’s various biological aspects and characteristics:

  1. Choose the Tree for Analysis: Select the tree you want to analyze. Consider the tree’s species, age, and location, as these factors can influence the analysis.
  2. Gather Relevant Information: Collect information about the tree, such as its species, age, history, and any known issues or concerns.
  3. Visual Inspection: Conduct a thorough visual inspection of the tree to assess its overall health and condition. Look for signs of distress, such as dead or damaged branches, discolored or diseased leaves, and unusual growth patterns.
  4. Tree Anatomy Analysis: Examine the tree’s anatomy, including the roots, trunk, branches, leaves, and any flowers or fruits. Check for any visible abnormalities or structural issues.
  5. Measurements: Take measurements of various tree characteristics, including the tree’s height, trunk diameter (diameter at breast height or DBH), and crown width. These measurements can provide valuable data for analysis.
  6. Bark and Wood Inspection: Inspect the bark and wood of the tree. Look for signs of damage, such as cracks, cankers, or discoloration. Note any presence of fungi, lichens, or insects on the bark.
  7. Leaf and Needle Analysis: Examine the leaves or needles for color, size, shape, and any signs of disease or pest damage. Collect samples if necessary for further laboratory analysis.
  8. Root Examination: If possible, investigate the root system of the tree. Look for root health, evidence of root decay, or issues like girdling roots that may constrict the tree.
  9. Environmental Assessment: Consider the tree’s surroundings, including factors like available light, air quality, and the presence of nearby structures or potential sources of stress.
  10. Disease and Pest Assessment: Inspect the tree for signs of disease, such as cankers, wilting, or unusual growths. Look for common tree pests and the damage they may cause.
  11. Invasive Species Check: Determine if the tree is at risk of infestation by invasive pests or pathogens that may not be native to the area.
  12. Genetic Assessment: If conducting a genetic analysis, collect samples for genetic testing or analysis to understand the tree’s genetic makeup and heritage.
  13. Climate and Weather Conditions: Consider the tree’s exposure to climate conditions, including temperature, precipitation, and wind, which can affect its health.
  14. Data Recording: Document all findings and measurements using photographs, notes, and sketches. Organize the information for future reference.
  15. Preservation and Care Plan: Based on the analysis results, develop a plan for tree preservation and care. This may include pruning, fertilization, disease or pest management, or other specific actions to enhance the tree’s health and longevity. Conducting a biological analysis of a tree requires careful observation and an understanding of tree biology to ensure an accurate and thorough analysis, especially for older or significant trees.

2.2.3. Pathological analysis

When the disease appears, it is necessary to sample the plant material and adhere to the following instructions:

Take a sample representative of the problem. If the plants are small, take a few of them, do not take dead plants, but those that are in the process of dying. DO NOT add moisture to the sample. Samples must be fresh. Be sure to include as many recognizable stages of the disease as possible if they are visible. DO NOT expose the sample to heat or freezing, do not crush it. If it is necessary to analyze the whole plant, dig it out of the ground in order to preserve the root. Cover the root ball with a bag or plastic to keep the soil in contact with the roots and prevent them from drying out. Take a sample before applying the pesticide. Pesticides once applied can make accurate diagnosis difficult. When sampling insects, soft-bodied insects can be placed in isopropyl alcohol in a vial. Live insects should not be taken, and dead insects should be placed in a solid container so that they are not crushed. Take a few samples. Plant tissue showing damage from insects should be placed in a plastic bag. Large trees that are dying require the selection of specific parts for analysis. Photos of the entire tree or shrub can be very useful. 

LEAF SAMPLING: Selecting leaves that are partially green and partially symptomatic allows the lab to check for fungi, bacteria, and viruses that are causing symptoms on the leaves. Leaf samples can only be tested for viruses, bacteria, fungi and insect damage. Symptoms can be an indication of what is happening in the root or lower in the stem. The whole plant may be necessary to find the problem.

STEM AND BRANCH SAMPLES: Check the stem or branches for wounds (dark, split or sunken areas). Sampling branches that are no longer than 60 cm. Scrape the symptoms from the trunk of large trees or take a piece of bark if possible. The pathogen will be most active in the demarcation zone, where dead tissue meets living tissue. Put everything in a paper bag.

ROOT AND SOIL SAMPLES: Plants often die out due to root problems. Collect fine roots near the drip line of the tree. Collect soil from the top 20 cm, place in a plastic bag and bury the roots in the collected soil.Stem and branch samples: Branch samples can only be evaluated for insect, fungal and bacterial damage if symptomatic tissue is present. If symptoms (fungal bodies, canker lesions, vascular striations/discoloration) are present on or in the branch, it is not necessary to take other parts if this is considered the primary problem.

SAMPLE ANALYSIS METHODS

Microscopic examination – by examining symptomatic tissue that has active growth, the pathologist can determine whether the problem is bacterial or fungal. Fungal pathogens that produce spores in or on symptomatic tissue can be identified using a microscope. Microscopic examination can show morphological details that help identify the pathogenic organism.

Moist chamber incubation – placing symptomatic plant tissue in a moist chamber for a short period of time will encourage the growth of any fungal pathogens present. The sample is then examined under a microscope. Different fungi grow at different rates, so results are visible in 2-3 days, or it may take weeks before the pathogen appears and can be identified.

Cultivation allows the isolation and separation of organisms found in plants. The causative agent (bacterium or fungus) is isolated from the plant and grown on a specialized medium in Petri dishes. The morphological characteristics of the pathogen in the pelvis (color, shape, size, sporulation of the body, etc.) are specific to the organism and help in its identification. The diagnostic time of the sample depends on the growth rate of the respective organism.

Enzyme immunoassay – can detect proteins belonging to certain microorganisms. It is used in

medicine, veterinary medicine and diagnostics of plant diseases for many years. It is based on specific antibodies that can recognize proteins that are specific for pathogens. It is a sensitive test with a high level of accuracy. Fungi, bacteria and viruses can be diagnosed.

DNA fingerprinting – polymerase chain reaction (PCR) can quickly detect an organism’s unique DNA. It is very sensitive, fast and can detect a low number of organism-specific genetic molecules. PCR can detect the presence of an organism regardless of whether it is dead or alive in the tissue, which other methods cannot.

2.3. Risk Assessment and Management

PLANT PROTECTION METHODS

Cultivation of resistant varieties – when purchasing planting material, you should always look for information on their resistance to the most important diseases and pests.

Agrotechnical measures – new planting material must not be planted in the place of diseased trees (some pests can move to a young tree). Excessive nitrogen fertilization increases the sensitivity of plants. Insufficient nutrition can be the cause.

Mechanical measures – collection of all developmental forms of pests, removal of diseased plant parts and their burning.

Physical measures – use of high temperature (water vapor) to suppress pathogens in the soil (for planting material)

Biological measures – the use of living organisms to control plant pests. Plant pests have their enemies, other insects, bacteria, fungi and viruses that attack pests.

Plant quarantine – belongs to the group of administrative measures against the causative agents of plant diseases. Trade in plants, especially seeds and planting material, caused the spread of many important and dangerous parasites. The phytosanitary service has the task of carrying out phytosanitary control during the import, export and transit of planting material, plant parts and seeds. Each shipment must be accompanied by a Phytosanitary Certificate.

2.3.1. Integrated Plant Protection

According to the Food and Agriculture Organization (FAO) of the United Nations, integrated plant protection is the assessment and application of all available plant protection measures and other measures that prevent the development of populations of harmful organisms, while at the same time reducing the risk to human health and the environment to the lowest possible level.

Chemical protection is not and should not be the only way to control plant diseases, pests and weeds. We should strive for integrated protection, i.e. protection with a system of various measures that will prevent the occurrence of diseases and pests in such an intensity that they could cause us economic damage. This includes the cultivation of more resistant varieties and agrotechnical measures. When these measures are not sufficient, and greater damage is expected, chemical protection should be used in a professional and rational way, which will disturb the balance as little as possible, that is, destroy the natural enemies of the intruder and pollute the environment. Integrated plant protection includes the following measures: quarantine measures, selection of resistant varieties, agrotechnical measures, mechanical measures, physical measures, biological measures.

Integrated plant protection requires competence in three areas: prevention, monitoring and intervention.

PREVENTING PEST BREEDING – includes a number of practical strategies that fit local conditions. MONITORING plantations regarding the development of pests and natural control mechanisms – includes searching for pests (harmful insects, diseases and weeds) and determining if, when and how to intervene. INTERVENTION when control measures are necessary – includes physical, biological and chemical measures to preserve the economic value of crops with minimal impact on the environment.

2.3.2. Chemical Plant Protection Measures

The largest number of pests, plant diseases and weeds are controlled by chemical means. These are means for chemical protection of plants – pesticides.

Pesticides are based on one active substance, but there are dozens of products and preparations on the market that contain the same active substance.

The impact of pesticides on ecosystems is multiple, depending on the selectivity of the pesticide, how long it takes to break down and how long it accumulates in the soil, water and air as a side effect of long-term use. The aforementioned is manifested in the impact on animals and plants, and in turn on people. Pesticides after application remain accumulated in plants as well as on their surface, thus entering the food chain of many wild and domestic animals, and ultimately of humans themselves. They can also be found in microorganisms at the bottom of the food chain. By changing the substance in the food chain, this cycle is repeated all the way to the organisms at the top of the food chain, where the highest concentrations of pesticides can be found.

Pesticides remain in the environment because they do not break down biologically, that is, because there are no microorganisms to break them down. By applying different techniques for removing pesticides from the environment, attempts are made to avoid limitations in order to make different remediation processes more effective. Today, the mechanisms of low-temperature thermal desorption, phytoremediation, bioremediation and incineration are mostly used. Each method has its advantages and disadvantages. Under ideal conditions, the remediation process should completely degrade the compound without forming intermediates.

Bioinsecticides – a natural enemy based on Bacillus thuringiensis.

2.3.3. Precautions

Any plant protection agent can be toxic to humans, domestic animals, game, birds, fish and bees to a greater or lesser extent. In addition to the mouth, agents can enter the body by inhaling droplets, dust particles or steam through the nose, and many penetrate through undamaged skin, so any contact with them can be dangerous. Some agents can also damage the plants treated with them (phytotoxicity). This is the reason why you should carefully read the instructions, in order to check which type a product is intended for. The most dangerous phase of handling pesticides is the preparation of the product. Any contact with the skin and its inhalation should be completely prevented. Protective equipment is most often used for the application of pesticides: impermeable gloves, rubber or plastic boots, work suit, headgear, face shield made of transparent plastic, a respirator is required in cases when handling agents for which this is specifically indicated. Do not spray or dust against the wind, do not smoke or eat, do not blow out blocked sprayers with your mouth. The poisoned surface should be marked with a board. Empty packaging should be disposed of in the appropriate prescribed manner. The most common signs of poisoning with plant protection products are: sweating, abundant salivation, watery eyes, difficulty breathing, cramps, weakness, fatigue, headache, dizziness, vomiting, tremors and fainting. When poisoning is suspected, the work should be stopped immediately, the contaminated protective clothing should be removed, all exposed parts of the body should be washed and the work area should be vacated. If the agent was taken by mouth, you should induce vomiting, take 3-6 dcl of water with one to two tablespoons of medical charcoal, and then a laxative. If the symptoms continue, you should seek medical attention.

Conclusion

In conclusion, tree assessment, including tree inspection and biological analysis, plays a crucial role in preserving the health and longevity of trees, ensuring the aesthetic appeal of the landscape, and protecting the environment. By conducting regular tree inspections and thorough examinations of trees, we can detect early signs of diseases, infestations, or other issues. This early detection allows for timely intervention, such as applying treatments or removing diseased trees, preventing the spread of diseases to other trees and maintaining overall tree population health.

Visual Tree Assessment (VTA) is a vital tool in the field of arboriculture, enabling the systematic evaluation of tree health and structural integrity. By following a structured set of steps and conducting a thorough inspection, arborists and tree care professionals can identify potential issues, assess risks, and provide informed recommendations for tree management.

Biological analysis of trees, encompassing tree anatomy, physiology, genetics, ecology, disease and pest management, root structure, and more, provides valuable insights into tree biology and the ecosystem. Understanding the ecological role of trees and their interactions with the environment is crucial for sustainable forest management and urban forestry.

When pests and diseases are identified, conducting a pathological analysis and choosing the right method for sample analysis are vital steps. This includes microscopic examination, moist chamber incubation, cultivation, enzyme immunoassay, and DNA fingerprinting, all of which help identify and manage the causal agents of tree diseases.

Risk assessment and management in tree care involve various methods, including the cultivation of resistant tree varieties, agrotechnical practices, mechanical and physical measures, biological control, and plant quarantine. These methods aim to minimize the impact of harmful organisms while safeguarding the environment and human health. Additionally, chemical plant protection measures, such as the use of fungicides and insecticides, should be employed with caution and in accordance with recommended safety practices to mitigate their potential environmental impact.

Integrated plant protection, incorporating various measures, ensures a comprehensive approach to managing tree health and mitigating risks, emphasizing the importance of prevention, monitoring, and intervention. By adopting these practices, we can better protect our trees and the environment in which they thrive.

Quiz

Test your knowledge in the following quiz and see if you understood the contents of this section:

Literature

  • Roloff, A. (2019). Baumpflege. Ulmer Verlag. Stuttgart.
  • Butin, H. & Brand, T. (2017). Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume. Ulmer Verlag. Stuttgart.
  • Hartmann, G. & Butin, H. (2017). Farbatlas Waldschäden- Diagnose von Baumkrankheiten. 4., aktualisierte und ergänzte Auflage. Ulmer Verlag. Stuttgart.
  • Brandstetter, M. et al. (2015). Holz zerstörende Pilze. 6. Auflage. Bundesforschungs- und Ausbildungszentrum für Wald, Naturgefahren und Landschaft (BFW). Wien.
  • Agrios, G. (2005). Plant Pathology. Fifth edition. Elsevier Academic Press. Burlington.
  • Callan, B. (2001). Introduction to Forest Diseases. Pacific Forestry Centre. Victoria.

Appendix

The most common urban tree diseases

Maple Anthracnose – Aureobasidium apocryptum (syn. Kabatiella apocrypta), Discula i Colletotrichum). The symptoms are characterized by dark, irregularly shaped, angular spots or lesions primarily occurring along the midrib, primary veins, and leaf margins. Lesions on Norway maple are typically narrow, purplish-black streaks along leaf veins. As for the sugar maple, lesions occur along the primary veins and appear as large, brown blotches. As regards the Japanese maple, lesions occur along primary veins and leaf margins and the lesions can appear both tan or black in color. Anthracnose fungus overwinters within senescent leaf tissue and in infected twigs and buds. Spraying with copper hydroxide + mancozeb, thiabendazole, mancozeb, and propiconazole.

Oak Anthracnose – Apiognomonia errabunda (previously known Discula). In addition to the genus Quercus, it affects the genera Fagus, Castanea, and Tilia. Symptoms first appear as water-soaked, blighted leaf margins or as blotches along the primary veins as new foliage develops. Over time, the lesions become dry, papery, and gray. Pubescent leaves can become distorted or shriveled and may be shed prematurely from the canopy. Prune and discard dead stems and branches and thoroughly remove all fallen leaves in autumn and spring as they harbor the fungus and allow inoculum to remain at the site.

Figure 35: Apiognomonia errabunda, Fagus.
Source: Butin H. & Brand T (2017). Apiognomonia errabunda, Fagus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.85). Ulmer Verlag

Plane tree Anthracnose – Apiognomonia veneta, infects Platanus occidentalis. Active fungal growth within one-year-old branches kills the tips, leading to shoot blight. Visible symptoms include angular leaf spots and blotches on the foliage (especially along the midrib), shoot and bud blight, and splitting stem cankers on twigs and small branches. The fungus often grows in older branches beneath dead twigs, creating perennial cankers. The following chemicals are approved for use in landscape settings: copper hydroxide, copper hydroxide + mancozeb, copper salts of fatty and/or rosin acids, copper sulfate, debacarb + carbendazim, mancozeb, propiconazole, and thiabendazole hypophosphite.

Figure 36: Apiognomonia veneta infects Platanus occidentalis.
Source: Butin H. & Brand T (2017). Apiognomonia veneta. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.150). Ulmer Verlag

Phytoplasmas

Ash Yellows – Phytoplasma, in the genera Fraxinus and Syringa, leads to the development of witches’ broom, and the affected trees die within three years. Witches’ brooms occasionally form at the root collar or the lower trunk, but some infected trees can die without developing symptoms. Nonetheless, witches’ broom formations are the key diagnostic symptom.

Elm Yellows – Ophiostoma novo-ulmi  Elm yellows symptoms begin in mid to late summer with the chlorosis and drooping of petioles of turgid leaves and premature leaf loss. Symptoms abruptly appear within a few weeks and are visible throughout the crown. Yellowing will occasionally begin on scattered branches and over a couple of years spread throughout the crown. In some situations, trees wilt and die quickly without prior symptoms.  Within lower branches the inner bark (phloem) yellows (instead of the normal white color), then develops tan flecks, and eventually dies. It smells like evergreen.

Figure 37: Ophiostoma novo-ulmi.
Source: Butin H. & Brand T (2017). Ophiostoma novo-ulmi. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.150). Ulmer Verlag

Rust Diseases

Ash Rust -Puccinia. In late spring, yellow spots appear on the upper surface of ash leaves, as well as on petioles and green twigs. Within 10-14 days, orange fruiting structures form on the petioles, green twigs, and the underside of leaves. The leaf turns brown and falls off. Apply fungicide as the buds break open and repeat them while the foliage develops.

Figure 38: Puccinia, Mahonia Rust.
Source: Butin H. & Brand T (2017). Puccinia, Mahonia Rust. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.128). Ulmer Verlag

Cedar-Apple Rust –  Gymnosporangium spp., infects Malus, Juniperus i Crategus, Picea. Several weeks after infection, yellow spots begin to form on the surface of the leaves. By mid-summer, the spots turn orange to red and develop a swollen mass with cream-colored tendrils on the underside (known as aecia). Aecia release spores (aeciospores) that are dispersed by the wind to nearby juniper trees and shrubs from late summer to early fall. Initially, infected spruce needles and twigs do not show infection symptoms. During the following spring and summer, small green swellings develop, maturing only until the following spring.

Cedar-Quince Rust – Gymnosporangium spp.. On Juniperus, the pathogen produces orange- to red-colored pads of fungal tissue that swell from infected stems and branches in the spring (late April to late May). After periods of rain, the pads swell and become orange, gelatinous masses of spores that are dispersed by wind and splashing rainwater. While these cankers can girdle small branches, resulting in canopy dieback, infected branches often persist and the cankers become a perennial source of inoculum in the tree’s canopy. Fungicides are rarely  recommended to control cedar-quince rust, mostly because none have been found to be very effective.

Spruce Needle Rust – Chrysomyxa spp. In late winter to early spring, orange to yellow spots or bands appear on one-year-old needles. In late winter, the symptoms may be hard to detect, but when spring advances and bud break approaches in early to mid-May, the bands swell to produce waxy, yellow-orange pustules containing masses of rust-colored spores. Copper hydroxide or mancozeb can be effective and is labeled for use on spruce in the landscape.

White Pine Blister and Ribes Species – Cronartium ribicola. Infects five-needle pines, the host is black currant, R. nigrum. The disease is manifested by white bumps on the branches and trunk.

Figure 39: Cronartium ribicola, Ribes.
Source: Butin H. & Brand T (2017). Cronartium ribicola, Ribes. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.128). Ulmer Verlag

Vascular Wilts

Dutch elm disease – is a lethal vascular wilt disease of American elm (Ulmus americana) that is caused by Ophiostoma novo-ulmi and O. ulmi. The disease can also spread from infected to healthy trees through root grafts when elms are in close proximity to each other. When the bark is peeled or cut on affected branches, longitudinal brown streaks or stripes in the outer rings of the plant become visible. Protect American elms from infection through preventive fungicide injections at intervals of 1-2 years. Fungicides approved for use against Dutch Elm Disease (DED) include Arbortect 20S (thiabendazole hypophosphite), Alamo (Propiconazole), and Tebuject (Tebuconazole). Therapeutic injections can also be performed in combination with pruning affected branches.

Verticillium Wilt is caused by Verticillium dahliae . The most common hosts in landscape environments include maple Acer, Ulmus, Cotinus, Fraxinus, Liriodendron, Viburnum, Cercis, Catalpa, Magnolia, Gymnocladus dioicus, Elaeagnus angustifolia. Infections from Verticillium originate from the soil when the fungus attacks the root system of susceptible trees and shrubs and is transported into and through the canopy. Symptoms include marginal leaf scorch, leaf wilt, vascular discoloration, and branch dieback. Since there is a disruption in the transport of water and minerals to the affected branches and leaves, the symptoms are similar to those caused by root diseases. Verticillium is widespread in forest and landscape environments, but the disease’s prevalence remains relatively low in most cases, meaning that many plants can resist the pathogen when attacked. The impact of Verticillium wilt depends on the inherent susceptibility of a particular tree or shrub, the environmental stress that may be present (especially drought and root damage), and the virulence of the pathogen.

Figure 40: Verticillium dahliae, Cercis.
Source: Butin H. & Brand T (2017). Verticillium dahliae, Cercis. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.62). Ulmer Verlag

Needle Casts & Blights

Arborvitae needle blight – Phyllosticta, Infected by Phyllosticta have scorched needle tips and/or appear discolored (pale green to yellow), making them look dry. Infection begins at the needle tips and progresses towards the base. During humid and mild weather, black cushion-like fungal structures (pycnidia) burst through the epidermis on symptomatic needles, releasing large quantities of spores (conidia), which spread to nearby shoots to initiate new infections. Pestalotiopsis is a common pathogen on coniferous trees and shrubs, causing shoot and branch dieback in various species and varieties of Thuja, Chamaecyparis, Cryptomeria, and Juniperus. Fungicides: copper hydroxide, copper salts of fatty and rosin acids, metconazole, propiconazole, thiophanate-methyl, and mancozeb.

Figure 41: Phyllosticta, Robinia.
Source: Butin H. & Brand T (2017). Phyllosticta, Robinia. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.201). Ulmer Verlag

Brown spot needle blight – Lecanosticta acicola (earlier Mycosphaerella dearnessii). Symptoms often first appear as yellowing to browning of older needles in late spring and early summer. Once these symptoms develop, diseased needles are quickly shed from the canopy. Symptoms can also appear as brown, blighted needle tips. In these cases, needles may be retained in the canopy for longer periods of time as the base remains green. Fungicides are based on: azoxystrobin, benzovindiflupyr, copper salts of fatty and/or rosin acids, copper hydroxide, mancozeb, metconazole, phosphates, propiconazole and thiophanate-methyl. Fungicide application during the spring and early summer season can allow new needles to emerge and remain uninfected, restoring vigor to the tree.

Kabatina blight – The fungus Kabatina juniperi causes blight and cankers in members of the cypress family. Infected plants do not show symptoms during the season when they become infected. Early in the following spring, infected foliage turns pale green to yellow, infected shoots become brown and die. Black fruiting structures appear at the base of dead branches. Prompt application of fungicides after injury, especially if conditions are wet, can protect wounded tissue from infection and reduce significant secondary damage to affected plants.

Figure 42: Kabatina juniperii, Juniperus.
Source: Butin H. & Brand T (2017). Kabatina juniperii, Juniperus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.115). Ulmer Verlag

Lophodermium needle cast – There are many species of Lophodermium that attack pine (Pinus), spruce (Picea), true fir (Abies), juniper (Juniperus), false-cypress (Chamaecyparis), arborvitae (Thuja) and incense-cedar (Calocedrus) across the globe. Infected needles may develop yellow spots in late summer to early autumn before finally becoming yellow to brown. The symptoms first appear at the needle tips and will slowly progress to the needle base. Dead needles may not abscise normally and can linger in the canopy into the next growing season. Apply three to four treatments at 14–21 day intervals during this time. Labeled fungicides include: azoxystrobin, thiophanate-methyl, copper hydroxide + mancozeb, mancozeb and triadimefon.

Figure 43: Lophodermium seditiosum, Pinus mugo.
Source: Butin H. & Brand T (2017). Lophodermium seditiosum, Pinus mugo. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.145). Ulmer Verlag

Phomopsis blight – Phomopsis spp. cankers in junipers and several other members of the cypress family. Young foliage and shoots infected with Phomopsis turn yellow-green by late spring and brown by summer. Mature leaves are resistant and remain unchanged. Sometimes, black fruiting structures are visible at the base of the brown tissue. Timely application of fungicides protects young tissue from infection.,

Ploioderma needle cast – Phloeospora needle cast, caused by Phloeospora, affects two and three-needle pine trees. It infects species such as Pinus nigra, P. thunbergiana, P. rigida, P. resinosa, and P. mugo, Robinia, Ulmus, Castanea. Symptoms include browning and black spotting on the needles. Fungicides used to control it include copper hydroxide, copper hydroxide + mancozeb, and mancozeb.

Stigmina needle cast – caused by the fungal pathogen Stigmina spp., has emerged as an important foliar pathogen of blue spruce in the region. Colorado blue spruce (Picea pungens) and white spruce (P. glauca) are most commonly infected. Symptoms manifest as premature needle drop, particularly among older needles on the inner branches in the lower part of the canopy where there is shade and moisture. Broad-spectrum fungicides such as chlorothalonil, mancozeb, and copper salts of fatty and/or rosin acids can be used to control the fungi.

Figure 44: Stigmina pulvinata, Tilia.
Source: Butin H. & Brand T (2017). Stigmina pulvinata. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.256). Ulmer Verlag

Diseases of stems, branches, and cankers

Beech bark disease – is a disease-insect complex that involves both native and non-native scale insects and two species of the fungal pathogen Neonectria .  Insects that feed on the sap and chew on the wood can damage beech bark, and fungal infections can further harm the tree. Canker formations often develop on these injuries, distorting the appearance of the trunk. As a protective measure, it’s recommended to treat the lower part of the trunk with phosphites in the spring. However, care should be taken not to get the treatment on the leaves, as it can be phytotoxic.

Black knot of prunus – caused by the fungal pathogen Taphrina. In the months following infection, green stems become swollen, but the most distinctive symptoms are not yet visible. The disease is often first noticed early in the next growing season after infection (the second year), once the branches have swelled, taken on an abnormal shape, and turned black. To manage the disease, it’s recommended to spray with copper hydroxide, copper sulfate, captan, and thiophanate-methyl in the early stages of the disease.

Figure 45: Taphrina populi, Populus.
Source: Butin H. & Brand T (2017). Taphrina populi, Populus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.256). Ulmer Verlag

Botryosphaeria canker – Botryosphaeria canker is an important disease of many trees and shrubs in forests and managed landscapes. To date, there are more than twenty genera in the order Botryosphaeriales. The fungus forms small, black fruiting structures (pycnidia and/or pseudothecia) that emerge through the bark. They are often visible when using a hand magnifying glass.

Coral-spot nectria canker – Nectria cinnabarina attacks over 90 different genera of woody plants in landscape and forest settings. Common hosts in the landscape include: beech (Fagus), maple (Acer), elm (Ulmus) and honeylocust (Gleditsia). Coral-spot canker gets its name from the orange- to pink-colored, erumpent pads of fungal tissue that are frequently present on stems and branches of infected trees. These pads represent the fruiting bodies produced by Nectria, which are often very conspicuous in contrast with the bark. The pads release large volumes of spores that are splashed, washed or blown onto nearby branches, allowing the pathogen to establish new disease centers.

Cytospora canker – Cytospora, caused by the fungal pathogen Cytospora kunzei (also known as Leucostoma kunzei), is most common on Colorado blue spruce (Picea pungens), but many other conifers are susceptible to infection, including fir (Abies), pine (Pinus), hemlock (Tsuga), Douglas fir (Pseudotsuga), and larch (Larix). Pruning and removing infected stems and branches is a recommended best practice. Fungicides such as copper-based ones (copper hydroxide and copper salts of fatty and rosin acids), mancozeb, thiophanate-methyl, azoxystrobin, and phosphoric acid can be used to manage the disease.

Diplodia blight –   Diplodia (formerly known as Sphaeropsis sapinea), leads to needle blight, and the fungus typically establishes itself through some form of wound. Wounds caused by wind, insect feeding, pruning operations, or hail/snow/ice are typical infection sites. It attacks young shoots of the current season, resulting in shoot tip blight, stunted and/or withered needles, resin flow on declining or dead shoots, and overall dieback in the crowns near the branch tips. Treatment with fungicides based on azoxystrobin, benzovindiflupyr, boscalid + pyraclostrobin, copper salts of fatty and rosin acids, copper hydroxide, mancozeb, thiophanate-methyl, and trifloxystrobin is effective. Fungicides are most effective when applied just before bud break and at intervals of 7-10 days afterward.

Figure 46: Diplodia pinea, Pinus.
Source: Butin H. & Brand T (2017). Diplodia pinea, Pinus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.146). Ulmer Verlag

Phomopsis canker – Several species of Phomopsis cause canker of stems, branches and occasionally the main trunk, it can enter through buds or wounds from pruning, damage and progress down the stem. Primary symptoms of infection include wilting of leaves, burning of young shoots, sunken and darkened areas of stems with possible sap or resin flow, cankers on larger stems and branches, browning of vascular tissue when bark is scraped, and crown dieback.

Figure 47: Phomopsis juniperivora, Juniperus.
Source: Butin H. & Brand T (2017). Phomopsis juniperivora, Juniperus. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.115). Ulmer Verlag

Phytophthora blood canker – Several species of Phytophthora cause this disease, killing the bark and outer tissues of trees and shrubs. The most prominent symptom of the disease is a dark-coloured sap that oozes from the bark wounds. The fluid is usually reddish-brown and stains the surrounding crust as it flows downward. The infected bark is often waterlogged and stained, while the inner bark can show a range of abnormal colours (brown, bluish-green, orange and pink) depending on the particular species of Phytophthora present. Fungicides for treatment: azoxystrobin, carbendazim+debacarb (microinjections), copper sulphate , copper hydroxide, copper salts of fatty and rosin acids, mancozeb, metconazole, thiophanate-methyl and trifloxstrobin.

Phytophthora – oak (Quercus) bark canker, Plants infected with Phytophthora spp. should be destroyed because no chemical control measures are currently available.

Red ring rot of eastern white pine (Pinus strobus) – cancerous growth on the bark of white pine can attack other types of pine. Porodaedalea attacks sensitive white pines primarily through twigs and tops that have been attacked by the white pine weevil (Pissodes). Due to the attack of the fungus, the elliptical pockets of decay are lined with white cellulose fibers and thickened cancerous formations are formed.

Target tree bark cancer –  The fungal pathogen Neonectria, affecting over 60 species of deciduous trees and shrubs, colonizes sensitive trees through old branches. Perennial cankers develop on the main trunk and develop slowly with seemingly little effect on the overall health of the tree.Gleditsia triacanthos, Albizia julibrissin. Cancerous formations are often elongated and sunken with a coloured crust and eruptive fruiting bodies. Infected trees may have shoots with yellow and withered leaves, scattered crown dieback. Systemic fungicides such as azoxystrobin, thiophanate-methyl and phosphate should be applied directly to the site of cancer. Contact fungicides such as copper hydroxide and mancozeb could be used to protect newly developed shoots in spring and early summer.

Plant leaf diseases

Beech leaf disease – dark, intervening bands on the leaves; distortion of leaves; leaf thickening and general “leathery” texture; premature falling of leaves; death of buds and subsequent death of branches resulting in the death of the tree. Protection is carried out by treating the soil with nematicides, the systemic nematicide fluopyram, a combined product consisting of fluopyram + trifloxystrobin, and fluopyram + tebuconazole.

Botryosphaeria leaf spot – Botryosphaeria (black leaf rot). In the leaves, the fungus causes the appearance of purple spots, they increase in size and develop a brown color, the spots have brown rings with a purple edge, which gives the appearance of a frog’s eye. Cancer occurs in twigs, branches and trunks. Botryosphaeria can infect winter injuries. Slightly sunken reddish/brown spots appear on the infected areas of the bark. They increase and form ulcers, which increase every year. The bark usually dies and can be separated from the tree after a while. In older cancerous growths, pycnidia appear on the bark. Use fungicides when infected with fungus on the leaves.

Figure 48: Botryosphaeria dothidea, Sequiadendron.
Source: Butin H. & Brand T (2017). Botryosphaeria dothidea. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.232). Ulmer Verlag

Guignardia leaf spots in chestnuts – Guignardia aesculi, after flowering, pale green water-soaked lesions begin to form over the surface of the leaf. As the lesions spread, they become dry and orange-brown, the leaves may bend and wrinkle, becoming distorted by the end of the growing season. Unlike other foliar diseases, spots reach a certain size and stop developing. inside the spots, black dots can be observed, structures of fungi that carry spores. Fungicides are used to maintain the appearance of trees, but in most cases they are not justified.

Figure 49: Guignardia aesculi.
Source: Butin H. & Brand T (2017). Guignardia aesculi. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.31). Ulmer Verlag

Hawthorn leaf spot – Entomosporium mespili, numerous small red-purple spots develop on infected leaves, green twigs and fruit. A few weeks after infection, they often merge into purplish-gray-brown spots. By mid-summer, leaves prematurely turn yellow and fall from severely infected trees. Fungicides protect leaves and developing twigs in the spring when the buds open, spray at intervals as long as the weather is cool and wet.

Holly leaf spot – Coniothyrium spp.  Small to large yellow-brown spots of irregular shape appear during winter and spring on old holly leaves.

Oak leaf scab – Taphrina, the fungus grows inside the epidermis, under the cuticle, convex (raised) lesions appear on the upper surface of the leaf, while convex (depressed) appear on the underside. When many lesions develop on a leaf, they can coalesce and cause complete leaf collapse. It does not cause major damage, for a better appearance of the trees, spray with fungicides based on copper and mancozeb.

Phyllosticta leaf spot – caused by Phyllosticta spp., attacks Ilex, Kalmia, Hamamelis and other deciduous shrubs and trees. Causes leaf spots, leaf margin disease and complete collapse of infected leaves. High humidity and shade encourage disease outbreaks. Fungicides may have some utility against Phyllosticta when applied early in the season: copper salts of fatty and/or rosin acids, copper hydroxide, mancozeb, metconazole, and propiconazole.

Phytophthora – Infections usually start during warm and humid weather when the spores burst. Symptoms first appear as watery, dark green spots and blotches on the leaves. Within three days of infection, the affected tissue becomes brown and necrotic. Infections sometimes spread to succulent shoots. That is why it is not advisable to water the plants with leaves. The disease causes early leaf drop, and the pathogen then survives in the dead parts of the plant that remain moist over winter. Winter conditions are often too cold for pathogens to survive in the soil or in dried plant tissues. Nurseries and greenhouses are a haven for pathogens due to moderate winter temperatures. It attacks many herbaceous plants as well as coniferous and coniferous trees. Treatment with fungicides based on: copper salts of fatty and/or rosin acids, mefenoxam/metalaxyl, phosphoric acid.

Powdery mildew – Erysiphe, Phyllactinia and Podosphaera – grow on the surface (epidermal cells) of leaves and green shoots. Their growth appears as a dusty, gray to white coating on infected plant parts, they absorb nutrients through haustoria) that pierce the plant cells. When the diseases are more severe, the fungi grow in the inner cells, under the epidermis. Application of fungicides is recommended when powdery mildew symptoms first appear.

Figure 50: Erysiphe berberidis, Berberis thunbergii.
Source: Butin H. & Brand T (2017). Erysiphe berberidis, Berberis thunbergii. In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.43). Ulmer Verlag

Maple tar spot – caused by three species of Rhytisma fungi, the spots first appear after the leaves have reached full size, from late May to early June, as rounded, pale green, chlorotic spots with tiny fruiting structures developing in the center. Early leaf drop due to disease is most common in heavily shaded environments with minimal air flow and dense planting. The use of fungicides is not recommended for this disease.

Root and crown diseases

Agrobacterium – tumorous nodules on the roots of plants, rarely attacks conifers, mostly coniferous trees. Infected plant cells contain bacterial genes (actually a plasmid) that replace some of the genes of normal plant cells. Initially, the swellings on the roots and stems are small, light-coloured and round. They often increase and become more numerous during plant development, the leaves turn yellow and are small in size. The impact of stress in the environment such as high temperature, drought and cold can weaken the plant and affect the development of root diseases.

Phytophthora of the root and rotPhytophthora species are primary parasites of the fine roots and bark of plants and cause rotting of the entire root system. As a result of the attack, cancerous formations appear. Symptoms appear as crown dieback, stunted growth, yellowing and shriveling of leaves, early leaf fall, and resin/sap flow near the base of the trunk. Infected roots often appear brownish black, waterlogged and soft. Plants that grow in places with stagnant water or where there is seasonal flooding. Phytophthora produces swimming asexual spores. Phytophthora can survive for many years in the soil. Fungicides based on: copper salts of fatty and/or rosin acids, etridiazole, etridiazole + thiophanate-methyl, fosetyl-aluminum, mefenoxam/metalaxyl, phosphoric acid.

Pythium – Symptoms include stunting, wilting (dying) and crown lesions. There are often no fine roots, while the main roots are brown to black. Fungicides based on: azoxystrobin, copper salts of fatty and/or rosin acids, etridiazole, etridiazole + thiophanate-methyl, mancozeb, mefenoxam, phosphoric acid, thiophanate-methyl.

White root rotArmillaria – infection spreads from logs of large trees, attacks deciduous species and conifers, progressive death of crowns, stunted shoots, insufficient leaves / needles, pale coloured to chlorotic leaves, premature autumn color change, excessive narrowing and sap flow / resins at the base of the tree and sudden browning of leaves / needles in mid to late summer. Young trees die early. The fungus attacks trees under stress due to drought, insect attacks, lack of calcium in the soil, etc. Recently, biological protection has been carried out using antagonistic fungi from the genus Trichoderma.

Figure 51: Tree death caused by dark honey fungus (Armillaria ostoyae).
Source: Butin H. & Brand T (2017). Tree death caused by dark honey fungus (Armillaria ostoyae). In: Farbatlas Gehölzkrankheiten Ziersträucher, Allee- und Parkbäume (p.140). Ulmer Verlag

Root rot of Quercus spp. Symptoms of root and neck rot can be very general in nature, e.g. progressive dieback of the crown, stunted shoots, insufficient foliage, pale coloured to chlorotic leaves and premature discolouration in autumn to more open cavities at the base of the tree, seams or cracks with sap/resin flow. They attack sensitive wood through a wound on the root or lower trunk. Most often these are mushrooms: Armillaria spp., Inonotus, and Grifola frondosa and Meripilus giganteus.

The most common pests on urban trees

Defoliators

Bagworm (Thyridopteryx ephemeraeformis) – Attacks species like cedar, pine, sycamore, maple, redbud, and linden, causing defoliation of the host plant.

Figure 52: Thyridopteryx ephemeraeformis.
Source: Wikipedia (no date) Evergreen bagworm.
(Accessed 19.1.2024)

Box Tree Moth (Cydalima perspectalis) – the primary host is boxwood (Buxus spp.). This pest leads to defoliation, and can also cause the death of the host plant.

Figure 53: Cydalima perspectalis caterpillar.
Source: Wikipedia (no date) Cydalima perspectalis.
(Accessed 9.1.2024)

Elm Zigzag Sawfly (Aproceros leucopoda) – Hosts include elm and its varieties. Females cause minor leaf damage when laying eggs, while young caterpillars feed on the leaves, leading to partial or complete defoliation of the host plant.

Figure 54: Aproceros leucopoda.
Source: Wikipedia (no date) Apreceros leucopoda.
(Accessed 19.1.2024)

Fall Webworm (Hyphantria cunea) – Host plants include birch and wild cherry. Damage to host plants is primarily external, as these pests create a silver web around the leaves and skeletonize them.

Figure 55: Hyphantria cunea.
Source: Wikipedia (no date) Hyphantria cunea.
(Accessed 19.1.2024)

Larch Casebearer (Cleophora laricella) – host plants include all species of larch. It feeds on the leaves, leading to partial or complete defoliation.

Spongy Moth (Lymantria dispar) – host plants are oak, maple, birch, poplar, willow and conifers like pine and spruce. It causes defoliation and places significant stress on the host plants.

Figure 56: Lymantria dispar.
Source: Wikipedia (no date) Gubar glavonja.
(Accessed 19.1.2024)

Winter Moth (Operopthera brumata) – Preferred hosts are oak and maple, but it also attacks other deciduous plants like linden, ash, and white birch, causing partial defoliation of the host plant.

Piercing and Sucking Insects

Adelgids – small, aphid-like insects that form woolly masses on host plants, typically attacking coniferous trees.

Aphids (Alphididae) –  a type of aphid that pierces the leaves of host plants and feeds on their plant juices. Aphid feeding causes yellow spots on the host plant and can lead to leaf distortion.

Figure 57: Aphididae.
Source: Bugguide.net. (no date). Arthropods.
(Accessed 19.1.2024)

Balsam Twig Aphid (Mindarus) – a pest that attacks all types of firs. It causes the twisting of newly emerged needles, and the copious honeydew it secretes can lead to the sticking together of new shoots. The damage caused by this pest is visible on trees for 2-3 years.

Hemlock Woolly Adelgid (Adelges) – Host plants are coniferous trees. This pest weakens host plants, potentially leading to prolonged infestations that eventually kill the host tree.

Galls

Cooley Spruce Gall Adelgid (Adelges cooleyi) – Attacks several species of spruce. It feeds on new shoots, and its feeding can result in yellow spots and twisting of the needles.

Eastern Spruce Gall Adelgid (Adelges abietis) – Primarily infects spruce trees. It causes the formation of galls at the base of new shoots, which can reduce the overall vitality of the tree.

Figure 58: Adelges abietis
Source: StetniciHr (2017) Smrekova uš šiškarica.
(Accessed 18.1.2024)

Bark Beetles

Conifer Bark Beetle (Dendroctonus, Ips, Scolytus) – Primarily infects pine trees but can also attack spruce, fir, and other coniferous trees. It is a significant stress factor for coniferous trees, making them more susceptible to drying out. These beetles often target older trees because they do not produce enough resin, which serves as a natural repellent for this pest.

Elm Bark Beetle (Scolytus multistratius) – Host plants are elm trees. They attack the bark of the host plant.

Leafminers

Arborvitae Leafminer (Argyresthia thuiella) – Host plant is Thuja. It attacks the leaves, causing them to turn yellow and dry out.

Birch Leafminer (Fenusa pusilla) – primarily infects two species of birch, Betula populifolia and Betula papyrifera, and to a lesser extent black, yellow, and river birch. Larvae mine the leaves of the host plant, mainly appearing when new leaves emerge, resulting in yellow spots on the leaves.

Boxwood Leafminer (Monarthropalpus buxi) – Attacks all types of boxwood. It causes premature leaf drop and feeds on leaf tissue between the lower and upper leaf surfaces of the host plant.

Figure 59: Monarthropalpus buxi
Source: Wikimedia free media repository (no date) Pupa of the boxwood leafminer.
(Accessed 18.1.2024)

Nuisance Pests

Giant European Hornet (Vespa crabro germana) – attacks birch, willow, and poplar trees. They strip the bark from young plants, which can lead to the death of the host plant.

Root and Shoot Feeders

Black Vine Weevil ( Otiorhynchus sulcatus) – Attacks mountain laurel, yew, and some other evergreen plants. They feed on the leaves, leaving semi-circular notches. Additionally, they feed on the roots of the host plant. Apart from causing leaf yellowing, they can also lead to the death of the host plant.

Scale Insects

Scale insects (Coccoidea) are small, delicate insects with bodies covered with hard shields. Out of approximately 3,000 known species that are spread all over the world, about 90 species live in Central Europe.

Scale insects are an extremely important superfamily within the class of insects, which includes several physiological pests of great importance to fruit, vines, ornamental trees and shrubs. They are poorly mobile and cannot survive on annual cultivated plants, which, because of this, rarely attack. They feed mainly on proteins contained in plant juices. As plant juices consist mainly of pure sugar, some species secrete it in the form of a clear and sticky honeydew. Sexual dimorphism is strongly expressed in all earwigs: Females have reduced wings, legs and tentacles, but that is why they have a well-developed oral apparatus adapted to sucking. Most females have a wax shield (which gives them their name) on the upper and partly the lower side of the body, which is a product of the wax glands. With the help of this shield, they attach to the leaves or bark of plants.

Smaller males have only the front pair of wings, while the back pair has evolved into “stabilizers”, a pair of ball-like appendages, usually as long as the tentacles. Their eyes are well developed and their tentacles and legs are articulated. They have no mouth parts at all, which means they don’t feed at all. They reproduce sexually or by parthenogenesis. The larva is mobile, but very quickly attaches itself to the plant with the help of mouth parts. The female lays a large number of eggs under her shield. Their color varies according to the species from light ocher, yellowish brown to dark brown. Their size varies between 0.8 and 6 mm, and the largest species, Aspidoproxux maximus, can grow up to 38 mm. They are attached to the back or face of the leaf and to the surface of the woody parts of the plant. Scale insects are represented in Central Europe by a number of taxa of the family rank: Diaspididae, Asterolecaniidae, Ortheziidae, Margarodidae, Coccidae, Kermesidae, Pseudococcidae.

Wood Attackers

Asian Longhorned Beetle (Anoplophora glabripennis) – attacks trees such as maple, horse chestnut, birch, willow, poplar, and elm but does not infest conifers. It damages the bark of the host plant.

Bronze Birch Borer (Agrilus anxius) – Most commonly affects birch species such as Betula papyrifera, B. pendula, B. populifolia, while showing resistance in B. maximowicziana, B. platyphylla, and B. nigra. This pest creates tunnels in the vascular part of the tree, leading to girdling or the death of the host plant.

Emerald Ash Borer (Agrilus planipennis) – This pest attacks several ash species, including Fraxinus spp., F. americana, F. pennsylvanica, and F. nigra. It feeds by creating tunnels in the host plant’s bark and leaves, causing canopy dieback.

Pest Resistance

Resistance or resilience is when the action of a plant protection agent gradually loses its effectiveness against pests. The emergence of resistance occurs through selection, i.e. due to the frequent application of the same or related plant protection agents that kill sensitive specimens but leave few and unnoticeable resistant specimens alive. By interbreeding, the number of surviving resistant specimens increases, until finally, these resistant specimens become so numerous that the agent stops working. This is the reason to dispose of as many means as possible, in order to slow down the appearance of resistance by constantly changing them. Careless application of some agents can damage beneficial insects and plants that we wanted to protect from pests.

Identification of Urgency and Deadline for Suppression

In order to use plant protection products only when absolutely necessary, plantations should be inspected for the presence of pests. Only when their number exceeds a critical number should they be suppressed. The critical number shows the intensity of infection that is worth controlling, and for many pests this number is known. For example, for the flower bender, you should spray if there are at least 3-5 pests per tree. The inspection of the plantations also determines the optimal period of application, which depends on the number and developmental stage of the pest, plant development, meteorological conditions, etc.