Pests & Disease

Diseases of Trees and Shrubs in your Garden

Diseases of Trees and Shrubs in your Garden

Diseases of trees and shrubs
Diseases of trees and shrubs

Diseases were grouped into six groups according to the damage they cause with woody plants, namely: foliage diseases, collar and root rots, cankers, vascular wounds, viral diseases and diseases of origin abiotic. Plant diseases can be caused by a multitude of factors, including bacteria, fungi, molds, viruses and the environment. Common plant diseases Nursery and ornament are described below. See also the section “Compendium of pests and diseases as well as practices of recommended management ” from OMAF entitled Crop Protection Guide nursery and ornament.

Foliage diseases

Most plant diseases manifest themselves first on the foliage. However, the damage found in foliage does not mean necessarily that the leaves are “sick”. Indeed, it is not uncommon for the leaves to fade, turn yellow or brown, become covered with spots, deform or fall due to diseases that have nothing to do with the foliage. This change of state foliage is often attributable, for example, to vascular wilt, root rot or cankers elsewhere on the plant. Various non-infectious factors – such as drought, wet soils (excessive watering) or pollution of air – can also reveal symptoms similar to those of the disease on the foliage. It often happens that a problem the roots is not detected until the appearance of first symptoms on the leaves. Before you ask a diagnosis, it is, therefore, necessary to check whether the roots are white and firm, not brown and spongy.

Diseases of trees and shrubs
Diseases of trees and shrubs

Most leaf diseases are attributable to too high humidity or prolonged presence water on the leaves. The irrigation program must so make sure that crops that are sensitive to foliar diseases are only watered between the beginning and the middle of the morning and never at the end of the day or at night. This ensures that the foliage remains wet as short as possible and reduced to minimum risk of leaf diseases. Downy mildew, white leaf disease, leaf spot, anthracnose and red (falling needles) are common diseases that directly affect foliage. Rust causing spots in hardwoods are also described under the rubric “Chancres” on page 70 (due to symptoms which manifest themselves on intermediate hosts).

Gray mold (Botrytis)

This disease, caused by the Botrytis fungus cinerea, attacks the succulent tissues of the bulbs, stems, leaves, and flowers of plants. She often affects flowers and open leaves or senescent, succulent shoots and tissues damaged. Symptoms vary from one plant to the other. If the air is very humid, the mushroom will cause the appearance of a fluffy gray felt on infected parties.

Diseases of trees and shrubs
Diseases of trees and shrubs

High relative humidity contributes to the outbreak of the disease. We will, therefore, strive to reduce humidity by promoting good air circulation around the plants. Remove without delay the parts of wilted, senescent or sick, especially if rainy weather is forecast. Avoid irrigating crops by sprinkling on the foliage at the end of the day and never leave old leaves or withered flowers on the plants or on the surrounding ground.


Mildew appears at the beginning of the season. In very wet conditions, this mushroom can produce a fluffy felt (sporulation) from gray to brown on the underside of the leaves. When the humidity level goes down (in the middle of the morning, for example), the felt may disappear. The top leaves may have angular spots discolored pulling on the purple. This disease will gain ground if the weather is humid and if the air circulation is deficient. It is, therefore, necessary to reduce the moisture content by ensuring good air circulation around plants.

Diseases of trees and shrubs
Diseases of trees and shrubs

Remove discolored parts without delay, senescent or sick, especially when provides for rain. Avoid irrigation by sprinkling at the end of the day and never leave old leaves or withered flowers on the plants or on the surrounding ground.

White (powdery mildew)

Several species of mushrooms are responsible for white sickness. Spores are produced in white powdery masses on the surface of the leaves and young tissues. Spores spread by the wind and can cause secondary infections, but the different mushroom species do not spread not easily from one type of plant to another. The powdery mildew becomes visible after mid-season when it’s still hot during the day and nights are fresh. It can tackle many plants ornamental species, including species of the genus Syringa, Rosa, Ligustrum, and Amelanchier, as well as several herbaceous perennials. Like the mushroom remains mainly on the surface of the leaves, one can fight it with fungicides as soon as first symptoms. In some cases, such as roses, major malformations can occur produce.

White disease gives some plants Ornamental (eg Physocarpus) an appearance unusually thick and woolly. For others plants (eg Coreopsis, Sedum and Berberis), it is manifested as variable leaf spots. Since mycelium and white spores which characterize it are not always visible, the White disease is often misdiagnosed in these plants. To slow it down, choose a sunny spot enjoying good air circulation. In the wherever possible, use resistant cultivars or tolerant. Sprinkler irrigation during the day slows down the spread of fungi, but avoid using the same method late in the day, because it promotes the development of spores during the night.

Leaf spots and anthracnose

We group under the term “anthracnose” a certain number of conditions that lead to the formation of necrotic spots on leaves or fruits. This disease is also causing cankers on the twigs. Infected areas grow and become melt to form large necrotic spots as the disease grows. In severe cases, it follows a defoliation of the plant. Leaf spots in themselves result. However, a foliage loss repeated, season after season, can weaken the plant and cause his death. Cool, rainy and overcast spring weather promotes the appearance of fungi that cause leaf spots and anthracnose. Plants most common hosts belong to following genres: Catalpa, Populus, Juglans, Carya, Crataegus, Acer, Quercus, Platanus, Philadelphus, Sorbus, and Aesculus. Anthracnose of a plane tree (Gnomonia plantani) can wreak havoc important in Ontario; he is charged with death many trees in the eastern United States.

Diseases of trees and shrubs

Disease of Red Pine (Pinus), Spruce (Picea) and Fir (Abies) are susceptible to the fungi responsible for red diseases. The infection usually settles as soon as the new growth of the year appears. Of tiny black fruiting bodies can then develop along the infected needles, often in place of small white stomata. The infected needles during the previous season fall to the ground during the following summer and fall. In nurseries in Ontario, this disease can have serious consequences in older plants from one to four years old.

Apple Scab

Even though scab is a fungal infection that manifests itself in the fruit, this disease can also cause the appearance of purplish spots on the leaves of the species Malus. Apple scab (Venturia inaequalis) can result in severe defoliation of crabapples during cool and rainy periods between the middle and the late spring, that is to say, while the leaves out. Good farming practices allow minimizing the risks of the disease becoming developed. Plant trees in an open area and sunny where the air circulation is sufficient.

Ensure that trees are healthy and carry out a periodic pruning to favor the circulation of air in the foliage. As pathogen overwinters in fallen leaves on the ground, we must pick up the leaves at the end of the summer and remove them from the growing area (this measure can be reveal ineffective if there are other infected trees near). If it is not possible to remove leaves, try to shred them with a lawnmower as they fall. The leaves as well reduced to pieces, the microbial decomposition will be accelerated, which will decrease the production of fruiting bodies from the mushroom able to produce infectious spores the following spring. Wherever possible, cultivars will be used of apple crabs resistant to scab. If time is especially cool and rainy during the appearance of the leaves or that the symptoms of Scab apply, apply fungicides homologated. Make the first spray when the tips of the green leaves appear. Repeat treatment at 7 to 10-day intervals until the leaves harden.

Pyracantha scorch (bush-burning)

Scab of pyracantha (Venturia pyracanthae) destroys the fruits of cultivars of this species that are susceptible to the disease; for these cultivars, the recourse to the spray is therefore usually necessary From one year to another. Orange Glow cultivars, Orange Charmer and Mohave are more resistant.

Diseases of trees and shrubs
Diseases of trees and shrubs

Root and root rots

Pythium and Phytophthora soil fungi are responsible for various rots of collar and roots of a large number of plants. The presence of these fungi is most often attributable to over-watering or poor soils drained. In an infected plant, the lower part leaves – the petiole and the stem – take a spongy appearance. In the long run, the plant whole rot at ground level. In species, ornamental fungicides with preventive action (like Subdue MAXX) can be incorporated into a substrate at the time of stuffing to reduce the incidence of diseases caused by Pythium and Phytophthora.

Diseases of trees and shrubs
Diseases of trees and shrubs

Rhizoctonia and Fusarium mushrooms cause the formation of a brown chancre on the stem and roots of infected plants. For its part, Thielaviopsis fungus causes rot severe roots in infected plants. The tissues infected by this fungus are pulling more on black as brown, which makes it possible to distinguish it from other pathogenic fungi. If the seedlings are achieved, we will then speak of the damping off of seedlings. The Thielaviopsis fungus meets more often in ornamental floriferous plants as in the nursery plants.

branches and stems of woody plants. In the infected parts, the bark may fade, crack and remove easily. Once laid bare, the wood and the cambium die and their color turn brown or reddish brown to black. Fruiting pustules of the pathogen are usually visible on the dead bark. Chancres can gird completely a stem or branch, resulting in the dead parts of the plant. Cankers can be annual or multi-year. They usually attack plants with low hardiness and made vulnerable by factors like drought, inconvenience roots or poor soil quality. The chancres are attributable to fungi unhealthy parasites of the genus

Cytospora, Nectria, Valsa, and Hypoxylon. Plants healthy and vigorous usually resist disease through “compartmentalization” (ie, circumscribing the fungus inside the tissues callosum). Some chancres are of fungal origin, but the initial damage to tissue can also be attributable to sunstroke or geldégel play or be of mechanical origin. Some cankers (eg pine blister rust) white, chestnut blight, and walnut canker ash can seriously damage a forest. Monoculture in nursery and forestry is also likely to create the conditions conducive to the development of severe chancres.

The mushroom Cylindrocladium buxi is responsible a serious illness that causes wasting boxwood. It is manifested by the appearance of small discontinuous black chancres of the cylindrical form along the stems and lower branches. This mushroom kills precious cambial tissue under bark and causes burning of leaves. Those are however the cankers that make up the best indicator of this disease.
Sudden oak ink is a disease caused by a pathogenic fungus (Phytophthora ramorum) who seeks cool and wet environments. It’s about of a serious illness that caused the death of hundreds of thousands of oaks in California since it has been spotted in the 1990s.

ravages in several USA. The dead leaf searches remain on the branch, but take on a withered appearance. In hot weather and wet, an amber exudate may arise to new infection points. Flows on permanent cankers can appear on main branches, trunk or roots as and as the infection spreads. Infections by fire blight can have serious consequences if the weather is hot and rainy at a moment when the host plants are in bloom and that the leaves come out. Wind, rain, and insects spread the disease from one plant to another.

We have it fight by removing the cankers and cutting the wood at 30 cm under the infected part when the trees are dormant. We must also eliminate the sources of infection nearby, like apple trees or the abandoned pear trees. Pruning tools must be disinfected after each cut. A bactericidal spraying can be useful for the moment of flowering. For more information, see OMAF Publication 360, Guide fruit culture. Another bacterium (Pseudomonas syringae pv. syringae) may be at the origin of the decline of the Nursery material grown in containers. Of many deciduous woody shrubs are sensitive to this bacteria.

This is particularly the case of lilac (Syringa), syringa (Philadelphus) and ornamental cherry (Prunus). Symptoms are obvious as soon as the equipment is vented free in the spring. We can then observe shoots and blackened buds that are already dead. Sudden changes in temperature, combined with long periods during which leaves remain wet, seem to be conducive to the proliferation of bacteria in cultures of seedlings in containers. Some producers reduce the incidence of the disease by setting up networks drip irrigation to keep the foliage dry and delaying the removal of tarpaulins from plastic on sensitive and valuable species.

To reduce the pressure exerted by the disease, apply bactericides after the leaves fall in the fall and again at the beginning of the bulge buds and bud break in spring. Other bacteria cause the appearance of spots on the foliage. Pseudomonas species and Xanthomonas infect leaf tissues by time hot and humid and often appear in July, during exceptionally hot summers. They cause angular spots on the leaves of several species of leafy floral shrubs deciduous, like Hydrangea. The edges of the leaf spots are usually delineated by small ribs, creating a pattern that looks an aerial view of fields and roads. We can apply bactericidal products to prevent that the disease spreads to other foliage. However, pesticides do not allow to eliminate existing infections.

Tumors of the neck

This bacterial disease is caused by Agrobacterium tumefaciens. It causes the formation of galls at the rough surface and irregular which can be several centimeters. Most woody plants are sensitive to snail gall, including Rosaceae, charcoal, willow and nut trees. These injuries are found generally above the ground, near the collar, but also on the roots and the aerial parts plants, especially willows grafted on the stem

Diseases of trees and shrubs
Diseases of trees and shrubs

This disease is not a canker proper, but its effects are similar since it disturbs the vascular system of the plant and can cause annellations. The bacteria can remain dormant in the soil without the host, for about two years. She breaks into its host in favor of injuries inflicted in particular by tillage, pruning or grafting. We can reduce the formation of crown tumors on sensitive stem-grafted trees (eg, Salix) with use of the polyethylene tunnel method, which protects trees against the wind carry soil particles and bacteria depositor on the wounds. Apply a protocol sanitary system which includes the sterilization of grafting tools after each use. Remove or replace infected soil or leave the area fallow for two years before to cultivate it again. Pesticides are not always effective. Vascular wilting Invasion by bacteria or fungi of the vascular network of the plant can reduce the amount of sap that reaches the leaves, causing their wilting.

When the time is cool and wet, a brief respite is given with leaves, but the withering eventually becomes permed. The loss of foliage and twigs eventually leads to the death of branches and any the plant. The most striking examples are the Dutch elm disease (Ceratocystis ulmi) and verticillium wilt (caused by Verticillium dahliae). To avoid these diseases, use cultivars resistant and grow susceptible crops in soil free of pathogens. See the table 2-18, Woody plants resistant to Verticillium, on this page and Table 2-19, Woody plants sensitive to Verticillium, on this page.

Sometimes, you can save plants infected with Verticillium by strengthening them by pruning, fertilizing and irrigation. Like these pathogens live inside the plants, the applications fungicides on the surface are ineffective. The Verticillium fungus is a soil-borne pathogen who survives years in the soil. In the past, trees grown in the open field were reached by verticillium wilt following wounds repetition of the root system on the occasion of various pruning or tillage operations. Before planting trees that are vulnerable to Verticillium in a field, it is, therefore, necessary to have the ground to spot the possible presence of the fungus.

Virus diseases

Viruses are usually manifested by Foliage defects – mottling, deformation or waving – or by the abortion of flowers or the small size of the plant. There is no pesticide effective against viruses. The only remedy is to remove and destroy the affected plants in order to prevent come spread the virus to the rest of the plot. Most viruses are spread by insects or contaminated horticultural material (pruning shears, knives, saws, etc.). We can slow the spread of viral diseases by fighting against the populations sucking insects, such as aphids, thrips, leafhoppers, and mites. Disinfect all tools before getting serve again. It is also recommended to ship samples of plants with symptoms of illness at the Clinic of Phytosanitary Diagnosis (see Annex E, Services diagnostics, on page 90) for analysis. If possible, we will destroy the plants infected to prevent the spread of the disease to other sensitive crops.

Ash yellows

Affected plants suffer from a slowdown growth and atrophy, have small leaves, sometimes chlorotic, and present brooms of the witch (proliferation of shoots) at the end branches. The symptoms may vary according to the age of the plant.

Diseases of trees and shrubs
Diseases of trees and shrubs

Yellow Elm

The mycoplasmas responsible for this disease are probably brought by leafhoppers. Before mid-summer, the leaves of infected trees begin to turn yellow, twist and arch (Epinasty). Most often, infected leaves fall, and the branch dies shortly after.

Rose mosaic

Symptoms may vary by cultivar, the environment and the strain of the virus. We notice discoloration of leaves, speckling chlorotic, ring spots, green mottling pale or chlorotic, lightening of the veins or the formation of streaks and white mosaics or yellow.

Diseases of trees and shrubs
Diseases of trees and shrubs

Abiotic disorders

These conditions are mainly manifested in the foliage or the root system, or both. They are generally related to environmental conditions extremes (too hot, too dry, too wet, etc.). Abiotic diseases are at the origin of a wide range of problems in the measurement where they predispose plants to infections secondary. It can result in a gradual decline from the plant until death. These conditions are often attributable to climatic or soil conditions or the effects of human activity on the air and the soil. To remedy, we can eliminate or avoid the causes of damage (eg salt), use stronger plants or improve the cultivation methods. The exhibition sudden to a full sun, after a period of cloudy and rainy weather, can cause the foliage of trees to dry Acer and Fagus genera in late spring. The burning of the roots by the salt present in the soil is a frequent abiotic problem. She is attributable to contamination by deicing salt groundwater or runoff. The effects can be mitigated by increasing aeration of the soil and be watering the soil abundantly with low salt water.

Diseases of trees and shrubs
Diseases of trees and shrubs

The nature and intensity of the changes, all as the age, condition, and type of plant, are as many factors that affect the ability of the plant to adapt to the fluctuations of the environment. The Oak, maple, ash, and spruce are difficult to adapt at new conditions, like compaction soil, drought, excess water (which deprives roots of adequate ventilation), changes ground level or root breakage during work. Exotic species – such as spruce Norway – often have more difficulty adapting to Ontario’s climate as native species.


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