Category Archives: Disease – Broad Leafed Woody Ornamental

Tubakia (Actinopelte) Leaf Spot

What is Tubakia (Actinopelte) leaf spot? Tubakia leaf spot, formerly known as Actinopelte leaf spot, is a common late-season leaf disease of oaks. All species of oak appear to be susceptible to the disease, but oaks in the red oak group (such as black, red and pin oak) appear to be most susceptible.

Symptoms of Tubakia (Actinopelte) leaf spot on oak.
Symptoms of Tubakia (Actinopelte) leaf spot on oak.

What does Tubakia (Actinopelte) leaf spot look like? People often confuse symptoms of Tubakia leaf spot with those of oak anthracnose (see University of Wisconsin Garden Facts XHT1001). However anthracnose tends to develop earlier, in the cooler part of the growing season (May and June), while Tubakia leaf spot tends to develop later, during the warmer summer months (July and August). Initial symptoms of Tubakia leaf spot include small to large dark brown or reddish-brown spots on leaves. Spotting can occur on leaf veins, and death of the veins leads to collapse of leaf tissue beyond the point of infection. Small twig cankers may also form. When the disease is severe, Tubakia leaf spot can cause early defoliation of oaks. However disease usually develops late enough in the growing season that no long-term adverse effects on tree health occur.

Where does Tubakia (Actinopelte) leaf spot come from? Tubakia leaf spot is caused by the fungus Tubakia dryina (formerly Actinopelte dryina), a fungus that is most likely a fungus “complex” (i.e., a group of several distinct, but closely related fungi). Tubakia overwinters in infected twigs, and in dead leaves that hang from the tree or are scattered on the ground. Spores of the fungus are easily spread by wind and rain splash.  

How do I save a tree with Tubakia (Actinopelte) leaf spot? DO NOT panic! In most cases Tubakia leaf spot is a cosmetic disease. The disease will make a tree look a little ragged, but will not kill the tree. DO NOT attempt to use fungicide sprays to control this disease.

How do I avoid problems with Tubakia (Actinopelte) leaf spot in the future? You can reduce the number of spores that cause Tubakia leaf spot by removing and disposing of fallen, infected leaves. Leaves can be buried, burned (where allowed) or composted. When composting, make sure that your compost pile reaches high temperature (approximately 140°F). Also, make sure that your compost pile is routinely turned so that leaves on the outside of the pile eventually end up in the center of the pile. The combination of high temperature and decay of leaf tissue in a compost pile helps eliminate the Tubakia leaf spot fungus. Also, maintain good tree vigor by watering and fertilizing trees appropriately. Check with your local county Extension agent for details on how to properly care for trees.

For more information on Tubakia (Actinopelte) leaf spot: Contact your county Extension agent.

Thousand Cankers Disease – Pest Alert

What is thousand cankers disease? Thousand cankers disease (TCD) is a serious, potentially fatal disease of black walnut (Juglans nigra), a tree native to Wisconsin. TCD has not yet been reported in Wisconsin, but has been found in the western United States where it was first described in 2008. TCD more recently has been reported in the eastern U.S. in Tennessee, Ohio, Pennsylvania, Virginia, and North Carolina. TCD has been fatal to black walnut in all known cases. Other walnut species found in the western U.S. (e.g., California walnut (Juglans californica) and Arizona walnut (Juglans major)) appear to be much less susceptible. Butternut (Juglans cinerea), another tree native to Wisconsin, is also known to be susceptible.

Discoloration and tunneling under the bark of a walnut branch associated with thousand cankers disease leads to disruption of water and nutrient movement and eventual tree death. (Photo courtesy of Karen Snover-Clift, Cornell University,
Discoloration and tunneling under the bark of a walnut branch associated with thousand cankers disease leads to disruption of water and nutrient movement and eventual tree death. (Photo courtesy of Karen Snover-Clift, Cornell University,

What does thousand cankers disease look like? The first symptom of TCD is a yellowing of the leaves starting at the top of a walnut tree. Eventually lower leaves yellow and branches die. Death of the entire tree soon follows. Branches on trees with TCD have tiny holes (about the size of a pencil tip) made by a small beetle that is involved in the disease. Beneath the bark of symptomatic branches, well-defined dark black or brown cankers (i.e., diseased areas) form. Cankers eventually merge, disrupting movement of water and nutrients in the tree, leading to tree death.

Where does thousand cankers disease come from? Thousand cankers disease is caused by a combination of a fungus (Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis). The insect carries the fungus on its body and introduces the fungus into a walnut tree as it tunnels into the bark to feed. Walnut twig beetles spread the fungus locally as they move from tree to tree to feed. The fungus does not appear to spread by root grafts. Longer distance dispersal of the insect and fungus is possible when walnut seedlings, walnut firewood, and walnut wood products are moved by human activities. Walnut fruits have not been reported as a source of the insect or fungus.

How can I save a tree with thousand cankers disease? At this time, there are no formal recommendations for managing TCD. Researchers are attempting to develop treatment methods, including use of insecticides, fungicides and nutrient management, to help prolong the life of infected trees. Because TCD has not yet been reported in Wisconsin, the most important management strategy at this time is prevention.

How can I avoid problems with thousand cankers disease in the future? The best way to prevent the spread of TCD (as well as other tree pests and diseases)s to not move firewood! For information about the restrictions on moving firewood in Wisconsin visit the Wisconsin Department of Natural Resources website at Also be cautious about moving walnut transplants or other walnut products (especially those with the bark still attached), particularly if they are coming from an area where TCD has been reported.

For more information on thousand cankers disease or if you suspect you have seen this disease: Contact your county Extension agent or the Plant Disease Diagnostics Clinic (

* Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Diana Alfuth, Cory Bender, Laura Jull, Phil Pellitteri, Katie Schlichter and Wendy Kramper for reviewing this document.



What is tatters? Tatters is a leaf disorder affecting primarily members of the white oak group of oaks (i.e., oaks with leaves with rounded lobes) including bur, white and swamp white oaks. Members of the red oak group of oaks (i.e., oaks with leaves with pointed lobes), including red, black, pin and shingle oaks, as well as other types of trees, rarely display the disorder. Tatters was first documented in Iowa, Indiana and Ohio in the 1980’s, and since then has been documented throughout much of the Midwest.

Leaves with tatters appear shredded, or as if damaged by leaf-feeding insects.
Leaves with tatters appear shredded, or as if damaged by leaf-feeding insects.

What does tatters look like? Trees with tatters have leaves that are lacy and shredded. Some leaves may appear as though the tissue between veins has been neatly ripped out, while other leaves have an irregular pattern of damage. The amount of damage may vary from leaf to leaf and branch to branch. Adjacent oak trees may show different amounts of damage due to genetic variability, variation in environmental conditions, or other external factors. Tatters is commonly confused with anthracnose (see University of Wisconsin Garden Facts XHT1001), or damage by leaf-feeding insects.

Where does tatters come from? The cause of tatters has not been precisely determined. Tatters is thought to be a physiological disorder caused by damage to leaf tissue in the bud-stage, or during the opening of buds in the spring. Suggested causes of tatters include cold or herbicide injury or, much more rarely, injury due to insect feeding or egg-laying.

How do I save a tree with tatters? DO NOT panic. Trees affected with tatters often produce replacement leaves within two to three weeks after tattered leaves appear. However, producing new leaves weakens trees and may make them more susceptible to other diseases and drought stress. If your trees suffer from tatters, make sure they receive sufficient water (approximately one inch per week for established trees). If rainfall is insufficient, use a drip hose or soaker hose to apply supplemental water. To prevent competition for water and nutrients, remove lawn grass within the drip line of your trees and replace it with shredded hardwood, pine or cedar mulch. On heavy clay soils, use three inches of mulch. On other soils, use three to four inches of mulch. Be sure to keep mulch two inches from the main trunks of the trees. Fertilize trees as needed, but be sure to base any fertilization on a soil nutrient test.

How do I avoid problems with tatters in the future? There is no known method for preventing tatters. However, the occurrence of tatters one year does not guarantee that the same trees will suffer from tatters in subsequent years.

For more information on tatters: Contact your county Extension agent.

Powdery Mildew – Deciduous Woody Ornamentals

What is powdery mildew? Powdery mildew is a disease that occurs on the above-ground parts (especially the leaves) of many deciduous trees and shrubs, as well as herbaceous ornamental plants, indoor houseplants, and many agricultural crops. Conifers are not affected by this disease.

Many woody plants such as rose and lilac are susceptible to powdery mildew.
Many woody plants such as rose and lilac are susceptible to powdery mildew.

What does powdery mildew look like? The name of this disease is descriptive. The upper and (less frequently) lower surfaces of leaves, as well as stems of infected plants, have a white, powdery appearance. They look as though someone has sprinkled them with talcum powder or powdered sugar.

Where does powdery mildew come from? Powdery mildew is caused by several closely related fungi that survive in plant debris or on infected plants. These fungi are fairly host specific. The powdery mildew fungus that infects one type of plant (e.g., lilac) is not the same powdery mildew fungus that infects another (e.g., phlox). However, if you see powdery mildew on one plant, then weather conditions, usually high humidity, are favorable for development of the disease on a wide range of plants.

How do I save a plant with powdery mildew? DO NOT panic! For many trees and shrubs (e.g., lilac), powdery mildew is a cosmetic, non-lethal disease. For other plants (e.g., rose, ninebark) powdery mildew can cause severe leaf loss and even branch tip dieback. When a highly valued plant has had severe leaf loss due to powdery mildew for several years, you may want to consider using a fungicide for control. Fungicides containing dinocap, dithiocarbamates, myclobutanil, triadimefon, triforine, sulfur or thiophanate methyl are registered for use against powdery mildew. A combination of baking soda (112 tablespoons) and light weight horticultural (e.g., Sunspray®) oil (3 tablespoons) in water (1 gallon) has also been shown to be effective for powdery mildew control. Most products should be applied every seven to 14 days from bud break until humid weather subsides. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the fungicide in the safest and most effective manner possible. Also consider pretesting any product you decide to use on a small number of leaves or plants before treating a larger area to make sure there are no toxic effects, particularly when treating during warmer weather.

How do I avoid problems with powdery mildew in the future? Consider buying plant varieties that are powdery mildew resistant. This won’t guarantee that your plants will be powdery mildew-free every year, but should result in less severe disease when it occurs. Reduce the humidity around your plants by spacing them further apart to increase air flow. Be sure not to over-water as this can lead to higher air humidity as well. Finally, at the end of the growing season, remove and destroy any infected plant debris as this can serve as a source of spores for the next growing season.

For more information on powdery mildew: See UW-Extension Bulletin A2404 or contact your county Extension agent.

Rose Rust

What is rose rust? Rose rust is a common fungal disease found in much of North America (including the continental United States) and Europe. Rose rust affects many varieties of rose, though some varieties (e.g., hybrids) are more prone to the disease. Rose rust has been a perennial problem along the Pacific Coast of the United States where mild temperatures and high moisture are favorable for rust development. In the Midwest, extremes in winter and summer temperatures have tended to be less favorable for the disease. However, recent climate changes in the Midwest may lead to rose rust becoming more commonplace in the future.

Yellow spots on upper leaf surfaces with corresponding powdery, orange to black spots on lower leaf surfaces are typical of rose rust.
Yellow spots on upper leaf surfaces with corresponding powdery, orange to black spots on lower leaf surfaces are typical of rose rust.

What does rose rust look like? Rose rust often first appears on lower leaves, but eventually an entire plant can be affected. Typical symptoms include general yellowing of leaves followed by eventual leaf death. Affected rose stems (i.e., canes) can become curled and distorted. As the disease progresses, powdery orange or black, circular spots (called pustules) containing spores of the fungus that causes the disease form on the undersides of leaves, with corresponding yellow spots visible on upper leaf surfaces. Pustules may also form on stems and green flower parts (sepals). Rose rust usually develops in the spring and fall (when favorable mild temperatures and wet conditions are more common), but the disease can affect roses during the summer months as well.

Where does rose rust come from? Rose rust is caused by several species of fungi in the genus Phragmidium. These fungi specifically infect roses. Rose rust is often introduced into a garden on infected shrubs purchased from a nursery or other rose supplier. Once introduced into a garden, rose rust fungi can overwinter in rose leaf debris, as well as on infected rose canes. In the spring, spores produced in debris and on canes can blow to newly emerging rose foliage, leading to new infections.

How do I save a plant with rose rust? Control of rose rust is difficult once symptoms develop. Prune out affected canes and remove leaves as symptoms develop to prevent the spread of rust fungi to other rose shrubs. Destroy these materials by burning (where allowed by local ordinances) or burying them. In the fall, remove and destroy any remaining dead leaves and other rose debris to eliminate places where rose rust fungi can overwinter. If you notice a rust problem very early (before there are many symptoms), fungicide treatments may be useful for managing the disease; however, most fungicides work best when applied before any symptoms appear. If you decide to use fungicides for rust control, select products that are labeled for use on roses and that contains the active ingredients triforine or myclobutanil. Treat every seven to 10 days, and DO NOT use the same active ingredient for all treatments. Instead, alternate use of the two active ingredients listed above to help minimize potential problems with fungicide-resistant strains of rose rust fungi. Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use these products in the safest and most effective manner possible.

How do I avoid problems with rose rust in the future? Whenever possible, plant rose varieties that are less susceptible to rose rust (i.e., avoid hybrid varieties). Always inspect new rose shrubs for rose rust (and other diseases) prior to purchase. DO NOT bring diseased shrubs into your garden. Plant rose shrubs far enough apart so that their foliage does not overlap, and thin your roses on a regular basis. Proper planting and pruning promote good air circulation that will facilitate rapid drying of leaves and canes, thus making the environment less favorable for rust development. Avoid working with your roses when they are wet as you are more likely to spread rust spores under these conditions. Fertilize and water roses appropriately. Well-cared-for plants tend to be less susceptible to disease. When watering, apply water at the base of your shrubs (e.g., with a soaker or drip hose) rather than over the leaves (e.g., with a sprinkler). Watering with a sprinkler tends to spread rust spores and wets leaves and canes, thus providing a more favorable environment for rust infections to occur.

For more information on rose rust: Contact your county Extension agent.



Root and Crown Rots

What is root/crown rot? Root/crown rot is a general term that describes any disease of woody ornamentals where the pathogen (causal organism) attacks and leads to the deterioration of a plant’s root system and/or lower trunk or branches near the soil line. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

Discoloration of maple crown and roots typical of Phytophthora root/crown rot.
Discoloration of maple crown and roots typical of Phytophthora root/crown rot.

How do you know if your tree or shrub has a root or crown rot? Gardeners often become aware of a root/crown rot when they see above ground symptoms of the diseases. Affected plants are often slow-growing or stunted and may show signs of wilting. Often the canopy of an affected tree or shrub is thin, with foliage that is yellow or red, suggesting a nutrient deficiency. Careful examination of the roots/crowns of these plants reveals tissue that is soft and brown.

Where does root/crown rot come from? Several soil-borne fungi can cause root/crown rots, including (most frequently) Phytophthora spp., Pythium spp., Rhizoctonia solani, and Fusarium spp. These fungi have wide host ranges, and prefer wet soil conditions. Some root rot fungi such as Pythium and Phytophtora produce spores that can survive for long periods in soil.

How do I save a plant with root/crown rot? REDUCE SOIL MOISTURE! Provide enough water to fulfill a plant’s growth needs and prevent drought stress, but DO NOT over-water. Remove excess mulch (greater than four inches) that can lead to overly wet soils. Chemical fungicides (PCNB, mefenoxam, metalaxyl, etridiazole, thiophanate-methyl and propiconazole) and biological control agents (Gliocladium, Streptomyces, and Trichoderma) are labeled for root/crown rot control. However, DO NOT use these products unless you know exactly which root/crown rot pathogen is affecting your tree or shrub. Contact your county Extension agent for details on obtaining an accurate root/crown rot diagnosis and for advice on which, if any, fungicides you should consider using.

How do I avoid problems with root/crown rots? Buy plants from a reputable source and make sure they are root/crown rot-free prior to purchase. Establish healthy plants in a well-drained site, and when planting, place the root collar just at the soil surface. Moderate soil moisture. Add organic material (e.g., leaf litter or compost) to heavy soils to increase soil drainage and DO NOT over-water. Also, DO NOT apply more than three inches of mulch around trees and shrubs, and keep mulch from directly contacting the base of trunks and stems. Prevent physical damage (e.g., lawnmower injury) that can provide entry points for root/crown rot pathogens. Finally, minimize movement of root/crown rot fungi in your garden. DO NOT move soil or plants from areas where plants are having root/crown rot problems. DO NOT water plants with water contaminated with soil (and thus potentially with root/crown rot fungi). After working with plants with root/crown rot, disinfest tools and footwear with a 10% bleach solution, a detergent solution, or alcohol.

For more information on root/crown rots: See UW-Extension Bulletin A2532, or contact your county Extension agent.

Purple-Bordered Leaf Spot

What is purple-bordered leaf spot? Purple-bordered leaf spot (also called eye spot or Phyllosticta leaf spot) is a common, but primarily cosmetic disease that affects maples (in particular Amur, Japanese, red, silver and sugar maple). Phyllosticta leaf spot is similar in many ways to other foliar diseases of maple such as anthracnose (see University of Wisconsin Garden Facts X1001a) and tar spot (see University of Wisconsin Garden Facts X1126).

Purple-bordered leaf spot (l).  Within the leaf spots (r), small, black, pimple-like fungal fruiting bodies form (red arrows).
Purple-bordered leaf spot (l). Within the leaf spots (r), small, black, pimple-like fungal fruiting bodies form (red arrows).

What does purple-bordered leaf spot look like? Purple-bordered leaf spot leads to the formation of roughly circular dead areas (typically less than ¼ inch in diameter) on maple leaves. Spots have tan to brown centers and distinct purple, red, or brown margins. Tiny, black, pimple-like reproductive structures (called pycnidia) often form within the spots, and are diagnostic. As spots mature, the centers may fall out, leaving roughly circular holes.

Where does purple-bordered leaf spot come from? Purple-bordered leaf spot is caused by the fungus Phyllosticta minima which overwinters in leaf litter. In the spring, rain and wind move spores of the fungus from the leaf litter to newly developing maple leaves, where infections occur. Spores produced on infected leaves can lead to additional infections within the tree canopy throughout the growing season.

How do I save a tree with purple-bordered leaf spot? DON’T PANIC. Although purple-bordered leaf spot may look unsightly, the disease is usually only a cosmetic problem, rarely causing significant damage to mature and vigorously-growing trees. Occasionally, the disease may defoliate trees early in the growing season, but these trees are typically able to produce new leaves within a few weeks. Defoliated trees should be watered (about one inch of water per week), and properly fertilized (based on a soil nutrient test).

How do I avoid problems with purple-bordered leaf spot in the future? If available, select maple varieties that are resistant to purple-bordered leaf spot. Compost, bury or burn leaf litter from infected trees in the fall, or in the spring before trees releaf. Newly planted maples, and established maples that have been severely affected by purple-bordered leaf spot for several years, may benefit from treatments with a fungicide containing chlorothalonil, copper, mancozeb, neem oil, sulfur or thiophanate-methyl. Three treatments may be needed for adequate control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

For more information on purple-bordered leaf spot: Contact your county UW-Extension agent.

Plum Pox – Pest Alert

What is plum pox? Plum pox, also known as “sharka,” is a virus disease that affects stone fruits including plums, peaches, nectarines, apricots, and ornamental Prunus species. Cherries are resistant to most strains of plum pox, or at least do not show symptoms. The plum pox virus does not infect humans or animals. Plum pox occurs on stone fruit trees throughout Europe, in Chile, and was discovered in Pennsylvania in 1999. Plum pox doesn’t kill trees, but it causes serious crop losses by making fruit tasteless, deformed and unmarketable. The virus is spread locally by aphids and over long distances on budwood and planting stock. The strain found in Pennsylvania (D strain) is not carried on seed.

Plum pox symptoms on immature plum fruits (left), and a plum leaf (right). (Photographs courtesy of R. Scorza and obtained from West Virginia University at
Plum pox symptoms on immature plum fruits (left), and a plum leaf (right). (Photographs courtesy of R. Scorza and obtained from West Virginia University at

Why is plum pox important? Until its discovery in 1999 in peach orchards in two townships in Pennsylvania, the plum pox virus was unknown in North America. The discovery of a new stone fruit pest in a major stone fruit production region, and in the vicinity of at least one major fruit tree nursery, is cause for concern. Virus diseases of plants generally cannot be treated. Eradication of the virus would require destruction of entire orchards. In order to contain the disease, the affected area has been placed under quarantine, making it illegal to move stone fruit trees or budwood from the area. However, some spread of the virus may have already occurred in symptomless planting stock. Therefore, commercial growers and Extension personnel throughout North America need to be aware of plum pox symptoms in order to protect the stone fruit industry. Ornamental trees are an important reservoir for the plum pox virus. Extension personnel should be diligent when observing Prunus specimens whether submitted by commercial growers or homeowners.

What does plum pox look like? Symptoms vary depending on the host. On plum, leaves have pale green to yellow spots and blotches (see photo above). On peach, symptoms appear on the first leaves to expand as yellowish zones along veins. This symptom is difficult to distinguish from other causes of yellowing along veins such as nutrient deficiency. Plum pox is difficult to detect, because leaf symptoms are often restricted to only a few leaves per shoot, and infected trees are usually not stunted. On immature plum fruit, symptoms include green and yellow rings and blotches (see photo above). As fruit ripen, symptoms fade, but infected fruit drop from the tree prematurely. Symptoms on other Prunus fruits are similar to those on plum.

For more information or help in diagnosing plum pox: Contact Patricia McManus, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706-1598, phone: (608) 265-2047, fax: (608) 263-2626, email:, or contact your county Extension agent.

Oak Wilt

What is oak wilt? Oak wilt is a lethal fungal disease that affects virtually all species of oaks. Oaks in the red oak group (oaks with pointed leaf lobes) such as red, scarlet, black and Northern pin oak are most susceptible. Oaks in the white oak group (those with rounded leaf lobes) such as white, bur, post, and swamp white oak are less susceptible.

What does oak wilt look like? Initially, single branches on infected trees wilt and die. Leaves on these branches often bronze, or turn tan or dull green, starting at the tips or outer margins.

Marginal leaf bronzing or tanning is often an early symptom of oak wilt.
Marginal leaf bronzing or tanning is often an early symptom of oak wilt.

Leaves may also droop, curl, or fall from the tree. Infected trees eventually die. Oak wilt can kill oaks in the red oak group in less than one month. Oaks in the white oak group usually have less severe symptoms and are rarely killed in one season.

Where does oak wilt come from? Oak wilt is caused by the fungus Ceratocystis fagacearum which survives in infected living oaks and in oaks recently killed by oak wilt. Picnic beetles are attracted to mats of the oak wilt fungus in infected trees, pick up spores of the fungus on their bodies, then carry spores to healthy trees. Beetles are attracted to trees that have been recently wounded by wind or storm damage, or by pruning. Natural grafts between roots of oak trees growing near each other can also serve as a means by which the fungus moves from tree to tree.

How do I save a tree with oak wilt? Removing infected oaks is often the best way to manage oak wilt. Before removing trees, be sure to disrupt root grafts between infected and other nearby oaks. Destroy the wood from diseased oaks by burning or burying it. If you decide to keep the wood, remove the bark, pile it in one place and cover it with a heavy tarp, burying the tarp edges with soil until it is to be used. Injections of propiconazole are often recommended as treatments for infected oaks (and also as preventative treatments for healthy oaks). Unfortunately there has been little research indicating how effective such treatments will be for oaks commonly grown in Wisconsin.

How do I avoid problems with oak wilt in the future? Prune oak trees only during the dormant season when picnic beetles are not active. If pruning during the growing season is required (e.g., due to storm damage) immediately cover wounds with pruning paint. Carefully monitor oaks for oak wilt and remove infected trees promptly.

For more information on oak wilt: See UW-Extension Bulletin G3590 or contact your county Extension agent.

Nectria Canker

What is Nectria canker? Nectria canker is a common and potentially lethal disease that affects many species of trees and shrubs. This disease can cause significant damage on newly planted, as well as on established, trees and shrubs that are under stress.

For more information on Nectria canker:  See UW-Extension Bulletins A3281, A1771, A1817, A1730 and A2308 or contact your county Extension agent.
For more information on Nectria canker: See UW-Extension Bulletins A3281, A1771, A1817, A1730 and A2308 or contact your county Extension agent.

What does Nectria canker look like? Nectria canker is characterized by the production of sore-like wounds (cankers) that form on twigs, branches, and trunks. Cankers can form at leaf scars and wherever injuries occur. Injuries can be caused by pruning (particularly improper pruning), frost, hail, cracking from heavy snow or ice, sunscald, insects, or mammals. Cankers appear first as slightly sunken areas on the bark, but can grow for years, becoming target-shaped or elongated. Small branches girdled by cankers can wilt suddenly, fail to leaf out, and die.

Where does Nectria canker come from? Nectria canker is caused by two fungi, Nectria cinnabarina and Nectria galligena. These fungi survive in the margins of cankers where they produce numerous fruiting bodies (reproductive structures). Fruiting bodies can be cream, coral, orange, or red, and eventually darken to brown or black with age. Spores are dispersed by wind, water, and pruning tools. Cankers grow slowly, usually when the host is dormant, or under stress. Infected plants may hold the fungus in check by producing wound-closing (callus) tissue around the infected area.

How do I save a tree with Nectria canker? There is no cure for Nectria canker. Remove smaller branch cankers by pruning six to eight inches below the canker. Disinfect pruning tools after each cut by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). Trees with trunk cankers may live many years with the disease. Healthy trees are better able to slow the development of Nectria canker, so make sure that trees are watered and fertilized properly.

How do I avoid problems with Nectria canker in the future? Choose plants that are well-adapted to your local climate. Avoid any stresses to your trees and shrubs. Prune properly (see UW-Garden Facts XHT1014 and XHT1015), and avoid injury to root and trunks from lawnmowers. Remove grass from around the base of trees and shrubs, mulch properly, and water as needed to avoid drought stress.

For more information on Nectria canker: See UW-Extension Bulletins A3281, A1771, A1817, A1730 and A2308 or contact your county Extension agent.