Category Archives: Disease – Needled Woody Ornamental

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Specialty Crop, Disease - Vegetable

Herbicide Damage

July 24, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 03/01/2024

D-number: D0060

What is herbicide damage?

Herbicide damage is any adverse, undesired effect on a plant that is caused by exposure of that plant to a pesticide designed for weed control (i.e., an herbicide). Any plant can be subject to this problem.

Squash leaf distorted due to exposure to a common lawn herbicide.

What does herbicide damage look like?

Symptoms of herbicide damage vary depending upon the plant affected and the herbicide used. Common symptoms include stems that are flattened, or that twist or corkscrew. Leaves may have abnormal shapes, sizes or textures. In addition, leaves or leaf veins may yellow or redden. In severe cases, plants may brown and die. Some plants, such as tomatoes and grapes, are particularly susceptible to herbicide damage and can be used as indicators of unwanted herbicide exposure.

How does herbicide damage occur?

Herbicide damage results when an herbicide is misapplied. Herbicides for control of broadleaf weeds are occasionally applied with fertilizers as part of a lawn care program. If these products are applied too close to ornamentals or vegetables, or are applied when there is too much wind, then the herbicide can drift (move) from the area of application into a non-treated area. Often, drifting herbicides are difficult to detect by eye because they are extremely fine mists. They can better be detected by smell. Some herbicides readily produce vapors that can begin to drift several hours after application.

How do I save a plant that has been damaged by herbicides?

There is nothing you can do after plants have been exposed. However, most plants accidentally exposed to broadleaf herbicides applied with lawn fertilizers do not receive a high enough dose to kill them. Young growth exposed to the herbicide will be distorted and discolored, but subsequent growth will be normal.

How do I avoid problems with herbicide damage in the future?

When using a lawn herbicide, follow the application directions exactly. DO NOT apply the product too close to, or in a manner that will cause exposure to, non-target ornamentals or vegetables. To avoid drift, apply the herbicide when there is as little wind as possible (< 5 mph). Apply the herbicide at low pressure to minimize production of fine mists. Finally, use amine forms rather than ester forms of herbicides as amine forms are less likely to produce vapors.

For more information on herbicide damage:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Sharon Morrisey, John Stier, Ann Wied and Chris Williamson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Needled Woody Ornamental

Dothistroma Needle Blight

July 21, 2015 hudelson

UW Plant Disease Facts

Authors: Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0043

What is Dothistroma needle blight?

Dothistroma needle blight is a common needle disease that can affect over thirty species of pine trees. In Wisconsin, Austrian pines are most commonly and severely affected by this disease.

Brown needle tips are a typical symptom of Dothistroma needle blight.

What does Dothistroma needle blight look like?

Dothistroma needle blight first appears as dark green, water-soaked spots on the needles. The spots become tan, yellow, or reddish-brown, and may encircle the needles to form bands. The tip of the needle beyond the band eventually dies, leaving the base of the needle alive and green. Young trees are more likely to suffer damage than older trees. Seedlings (< 1 yr. old) can be killed within a year after infection.

Where does Dothistroma needle blight come from?

Dothistroma needle blight is caused by the fungus Dothistroma pini, which survives in diseased needles. Watch for tiny, black reproductive structures of the fungus (called pycnidia) that can be found erupting from the surface of infected needles. Spores are produced in these structures throughout the growing season, and infection by spores can occur at any time, but particularly during periods of wet weather. Symptoms appear from five weeks to six months after infection.

How do I save a tree with Dothistroma needle blight?

Copper-containing fungicides (e.g., Bordeaux mix) can help prevent new infections, but will not cure diseased needles. Typically a single fungicide application in early June is sufficient to provide protection of new foliage. However, a second application three to four weeks later will provide more complete control. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible. Several years of treatments may be needed to completely rid a tree of all infected needles (through natural needle loss).

How do I avoid problems with Dothistroma needle blight in the future?

DO NOT plant Austrian pines as they are extremely susceptible to Dothistroma needle blight. Consider using other conifers instead. If you decide to plant susceptible trees, make sure the trees are disease-free at the time of planting. Also, be sure to provide adequate spacing between the trees to ensure good airflow and promote rapid needle drying. If you have established trees that are suffering from Dothistroma needle blight, remove fallen needles from around the base of these trees as these can serve as a source of fungal spores.

For more information on Dothistroma needle blight:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

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

Thanks to Ann Joy, Laura Jull and Patti Nagai for r eviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc, Turf

Dodder

July 21, 2015 hudelson

UW Plant Disease Facts

Authors: Jennifer Clifford, Amilcar Sanchez, Trenton Stanger, and Brian Hudelson UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0129

Spaghetti-like dodder plants parasitizing carrots.

What is dodder?

Dodder is the name of several species of parasitic plants that are widely distributed in North America and Europe. Plants parasitized by dodder include alfalfa, carrots, onions, potatoes, cranberries, a variety of herbaceous and woody ornamentals, and many weed species. Parasitized plants become weakened, have reduced yields (in the case of agronomic crops), and can potentially die.

What does dodder look like?

Dodders lack roots and leaves, and also lack chlorophyll, the green pigment found in most plants. Dodders have slender, yellow-orange stems that cover infected plants in a spreading, tangled, spaghetti-like mass. From May through July, dodders produce white, pink, or yellowish flowers.

Where does dodder come from?

Dodders produce large numbers of seeds that germinate in the spring to produce shoots that attach to suitable host plants. Dodders penetrate host tissue, and absorb nutrients via specialized structures called haustoria. Once established on a host, the bottom of a dodder plant dies (thereby severing its connection with the soil), and the dodder plant becomes dependent on the host plant for water and nutrients.

How do I save plants parasitized by dodder?

On woody ornamentals, simply prune out dodder-parasitized branches. When small patches of dodder occur among herbaceous plants, apply contact herbicides such as 2,4-D early in the season, preferably before dodder seedlings have parasitized host plants. Keep in mind that use of contact herbicides will likely also kill host plants. Alternatively, cut or burn dodder and parasitized plants to keep dodder from spreading, and to prevent seed production. For widespread dodder infestations, a combination of frequent tilling, burning and herbicide applications may be needed to achieve control. Be sure to read and follow all label instructions of the herbicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with dodder in the future?

Dodder’s wide host range and ability to survive as dormant seeds in soil make eradication difficult. Preventing introduction of dodder is the best method of control. Use dodder-free seed, and be sure to clean equipment thoroughly after working in a dodder-infested area. Try to restrict animal movement between infested and non-infested areas as well. Depending upon the specific crop or location, use of pre-emergent herbicides containing DCPA, dichlobenil, propyzamide, or trifluralin may be possible to prevent germination of dodder seeds. Destroy actively growing dodder and any parasitized plants before the dodder produces seeds. In agricultural settings where dodder has been a problem, rotate away from susceptible crops and grow non-host crops (e.g., corn, soybeans, or small grain cereals). In conjunction with rotation, adequate control of weed hosts is critical to achieve control.

For more information on dodder:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Lis Friemoth, Matt Lippert and Dan O’Neil for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Needled Woody Ornamental

Cytospora Canker

July 19, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0037

What is Cytospora canker?

Cytospora canker is one of the most common fungal diseases of Colorado blue spruce. This disease can also affect Engelmann, Norway and white spruce, as well as balsam fir, Douglas-fir, European larch, tamarack, and white pine. Trees that are 15 years old or older and are at least 20 feet high often show symptoms of Cytospora canker. Cytospora canker can kill trees, but more often simply makes trees so unsightly that owners opt to remove the trees.

Death of lower branches of Colorado blue spruce typical of Cytospora canker.

What does Cytospora canker look like?

Cytospora canker usually first appears on lower branches and progresses up the tree, although individual upper branches may show symptoms as well. Needles on infected branches turn purple, then brown. Diseased needles eventually fall off, and infected branches die. Infected branches often ooze a bluish-white sap somewhere along their length.

Where does Cytospora canker come from?

Cytospora canker is caused by the fungus Cytospora kunzei (also sometimes referred to as Leucocytospora kunzei or Leucostoma kunzei). The fungus survives in infected branches and spores are spread by wind, rain splash, insects, birds, and mammals.

How do I save a tree with Cytospora canker?

Immediately remove and destroy any diseased branches by pruning them using the three-point method of pruning (see University of Wisconsin Garden Facts XHT1014, How to Properly Prune Deciduous Trees, for details). Prune only in dry weather. Between cuts, decontaminate pruning tools by treating them for at least 30 seconds in 10% bleach or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants). Decontaminating tools will help prevent movement of Cytospora kunzei from branch to branch and from tree to tree during pruning. If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

Bluish-white ooze often is present on branches affected by Cytospora canker.

How do I avoid problems with Cytospora canker in the future?

Perhaps the easiest way to avoid Cytospora canker is through proper tree selection, planting and maintenance. Avoid planting full-sized varieties of trees susceptible to Cytospora canker, particularly full-sized varieties of blue spruce. Instead plant dwarf tree varieties. Smaller trees will have canopies where air will more easily penetrate into the interior, thus drying branches and needles more rapidly. In general, a drier environment is less favorable for disease development. If you choose to plant a full-sized tree, leave adequate space between the tree and other trees in your landscape. Proper spacing will provide good air flow and again promote drier conditions that are less favorable for disease. Optimally, when trees are full sized, they should be far enough apart so that branches do not overlap. As a tree becomes well established, selectively prune branches to open up the tree’s canopy to further promote a drier environment.

Also minimize environmental stresses to any tree susceptible to Cytospora canker. Prevent water stress by avoiding soil compaction and by ensuring adequate soil drainage. During dry periods, make sure your tree receives approximately one inch of water per week either from natural rain or by applying supplemental water at the drip line of the tree (i.e., the edge of where tree branches extend) and beyond using a soaker or drip hose. To help maintain proper soil moisture, mulch out to at least the drip line of the tree. Use one to two inches of mulch on a heavier, clay soil; use three to four inches of mulch on a lighter, sandy soil. DO NOT pile mulch against the trunk of the tree; keep mulch approximately four inches from the trunk. Prevent nutrient stress by properly fertilizing your tree based on a soil fertility test provided by an accredited lab.

DO NOT use fungicide treatments for Cytospora canker control; fungicide treatments are not effective.

For more information on Cytospora canker:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Diana Alfuth, Jean Ferdinandsen, Lisa Johnson, Amy Sausen and Ann Wied for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental

Chlorosis

July 14, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0030

What is chlorosis?

Chlorosis is a common nutritional disorder of many woody ornamentals in Wisconsin, particularly in the southern and eastern parts of the state. Pin oaks are most commonly affected by chlorosis, although many other trees and shrubs (e.g., white oaks, red maples, white pines and rhododendrons) are also very susceptible.

Yellowing of foliage characteristic of chlorosis.

What does chlorosis look like?

Symptoms of chlorosis are easy to distinguish from those of other diseases. Affected leaves turn yellow, except for the veins, which remain green. In severe cases, foliage may turn brown and die. Symptoms can occur on isolated branches, or over an entire tree.

What causes chlorosis?

Chlorosis occurs when a tree or shrub is lacking certain micronutrients, in many cases iron or manganese. Lack of micronutrients in a tree may reflect a lack of these nutrients in the soil due to poor fertility. Often however, there are sufficient micronutrients, but they cannot be absorbed by a plant’s roots. Poor absorption of micronutrients is common in Wisconsin because of the high pH (alkalinity) of many soils.

How do I save a tree or shrub with chlorosis?

Chlorosis is rarely fatal and can be treated. For treatments to be effective, you must determine the exact cause of the chlorosis. Have the soil around an affected plant tested for micronutrients and for pH prior to applying any treatment. If the soil test indicates a lack of specific micronutrients, fertilize with these micronutrients. For example, chelated iron compounds can be used to increase the amount of iron in soil. If the soil test indicates a high soil pH, lower the pH by applying sulfur or ammonium sulfate. See University of Wisconsin Garden Facts XHT1151, Reducing Soil pH, for details. Contact your county Extension agent for information on soil testing and for tips on a treatment once you have determined the specific cause of your chlorosis problem.

How do I avoid problems with chlorosis in the future?

Plant trees and shrubs that are less susceptible to chlorosis. Also, make sure your trees and shrubs receive sufficient water (approximately one inch per week), as this will help plants with micronutrient uptake. During dry periods, use a drip hose or soaker hose to apply supplemental water. Remove turf from around the bases of trees and shrubs out to at least the drip lines, and apply shredded hardwood, pine or cedar mulch in these areas to help maintain soil moisture. On heavy clay soils, use one to two inches of mulch. On other soils, use three to four inches of mulch. Be sure to keep mulch four inches from the trunks of trees. If you decide to plant susceptible trees or shrubs, watch them closely for the yellowing characteristic of chlorosis, and apply corrective treatments as soon as symptoms appear. Treatments should always be based on the results of soil micronutrient and pH tests.

For more information on chlorosis:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Sharon Morrisey, Patti Nagai and Ann Wied for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc

Black Walnut Toxicity

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology; Laura Jull, UW-Madison Horticulture

Last Revised: 02/28/2024

D-number: D0021

What is black walnut toxicity?

Black walnut trees (Juglans nigra) produce a toxic substance (called juglone) that prevents many plants from growing under or near them. Related trees like butternut (J. cinerea) and shagbark hickory (Carya ovata) also produce juglone, but in lower concentrations than black walnut. Juglone occurs in all parts of black walnut trees, but especially in buds, nut hulls and roots. The toxic effects of a mature black walnut tree can extend 50 to 80 feet from the trunk of the tree, with the greatest toxicity occurring within the tree’s dripline. In this area, plants susceptible to juglone may wilt or die; plants tolerant to juglone will grow normally. Vegetables such as tomato, potato, eggplant and pepper, and ornamentals such as lilac, peony, rhododendron and azalea are particularly sensitive to juglone.

Wilting of eggplant due to black walnut toxicity.

What do the effects of black walnut toxicity look like?

Plants sensitive to juglone may be stunted, have yellow or brown, twisted leaves, exhibit wilting of some or all plant parts, and die over time. Often, the vascular (i.e., water-conducting) tissue of affected plants will be discolored. Symptoms may occur rapidly, even within a few days after sensitive species are transplanted into a walnut tree’s root zone. Alternatively, some plants may survive for years near a young walnut tree but then wilt and die as the tree increases in size. Black walnut toxicity can be confused with wilts caused by bacterial and fungal pathogens (e.g., see UW Plant Disease Facts D0121, Verticillium Wilt of Trees and Shrubs, and D0122, Verticillium Wilt of Vegetables), herbicide injury (see UW Plant Disease Facts D0060, Herbicide Damage), or drought.

How do I avoid problems with black walnut toxicity?

There is no cure for a plant affected by walnut toxicity. Removing a walnut tree may not be practical, as the tree could be the focal point in a landscape. In addition, even if a walnut tree is removed, juglones will not immediately be eliminated, because it is next to impossible to remove all root pieces from the soil and remaining pieces may continue to exude toxins for several years as they decay.

When establishing a garden around a walnut tree, try to plant species that are tolerant to juglone (see table on the reverse side). If you are growing sensitive species near a walnut tree, transplant them elsewhere in your garden. If you must grow sensitive plants near a black walnut, keep beds free of walnut leaves and hulls, and remove walnut seedlings as they appear. Grow shallow rooted woody and herbaceous plants, and improve drainage to help diminish the effects of juglone. Alternatively, consider building raised beds with wood, stone, or concrete barriers that limit root growth through and under the beds.

When disposing of bark and wood from a walnut tree, do not use these materials for mulch.

The information in the following table is intended to provide guidance in selecting plants to grow near walnut trees. Inclusion of plants in this table is based on observation, not on formal testing. In addition, the plant lists in this table are by no means exhaustive. Oftentimes the juglone sensitivity or tolerance of specific plants has never been observed or documented. Finally, sources often disagree on whether particular plants (e.g., columbine, lily, narcissus, tulip) are juglone sensitive or tolerant. Some varieties may be susceptible while others may be tolerant. Most plant species with conflicting information regarding their sensitivity or tolerance to juglone have not been included in the table.

	Sensitive to Juglone	Tolerant of Juglone
Vegetables	asparagus, cabbage, eggplant, pepper, potato, rhubarb, tomato	beans, beet, carrot, corn, melon, onion, parsnip, squash
Flowers	autumn crocus, chrysanthemum, forget-me-not, petunia, peonies	aster, astilbe, bee balm, begonia, black-eyed Susan, bluebell, calendula, crocus, daylily, ferns, grape hyacinth, some hosta varieties, hollyhock, impatiens, Jack-in-the-pulpit, Jacob’s ladder, marigold, morning glory, pansy, phlox, Siberian iris, squill, sweet woodruff, trillium, zinnia
Trees	alder, apple and crabapple, basswood, pine, spruce, silver maple, white birch	black locust, catalpa, Eastern redbud, hackberry, Canadian hemlock, hickory, most maples, oaks, pagoda dogwood, poplar, red cedar
Shrubs and Vines	azalea, blackberry (and most berries other than black raspberry), cotoneaster, hydrangea, lilac, mountain laurel, potentilla, privet, rhododendron, yew	arborvitae, bittersweet, black raspberry, clematis, currant, forsythia, euonymus, greenbrier, most honeysuckle, pachysandra, rose-of-Sharon, sumac, most viburnum, Virginia creeper, wild grape, wild rose, willow, witch hazel
Field Crops and Grasses	alfalfa, tobacco	fescue, Kentucky bluegrass, orchard grass, soybean, timothy, wheat, white clover

For more information on black walnut toxicity:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Lisa Johnson, Mike Maddox and Patti Nagai for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Needled Woody Ornamental

Armillaria Root Disease

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Michael Amman, UW-Madison Forest Ecology and Management and Glen R. Stanosz, Ph. D., UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0005

What is Armillaria root disease?

Armillaria root disease, also known as shoestring root rot, is an often lethal disease of tree and shrubs. It can affect almost any conifer or hardwood species, from seedling to maturity. Herbaceous plants can also be affected. Trees and shrubs stressed due to drought or defoliation can be particularly susceptible to Armillaria root disease.

White mats of fungal tissue called mycelial fans (arrow) may be present within and beneath the bark of stems and roots affected by Armillaria root disease.

Where does Armillaria root disease come from?

Armillaria root disease results from colonization of trees and shrubs by fungi in the genus Armillaria. These fungi produce tough, cord-like strands called “rhizomorphs” that grow from decaying stumps and roots through the soil. Infection of other trees or shrubs can result from penetration of intact roots by rhizomorphs. In late summer or early fall, honey-colored mushrooms of Armillaria fungi develop near the bases of colonized plants and produce spores that are distributed by wind. Infection also can occur after these spores germinate in wounds on stems or roots.

What does Armillaria root disease look like?

Above-ground symptoms of Armillaria root disease may include slow growth, yellowing and dwarfing of foliage, and thin crowns. Dieback of twigs and branches also may occur as the disease progresses. These symptoms may develop slowly and intensify over many years. However, trees and shrubs also may be rapidly killed, with leaves or needles suddenly wilting or browning on a plant that appeared healthy just days or weeks earlier. Bark on lower stems or roots may be killed and crack, with flow of resin common on conifers. Thin white mats of fungal tissue called “mycelial fans” may be present within and beneath killed bark. Stem and root tissue decayed by Armillaria fungi is often water-soaked, creamy to yellow in color, and spongy or stringy in texture. Rhizomorphs are commonly seen on or beneath the bark and growing from decayed stumps and roots.

How do I save a tree affected by Armillaria root disease?

There is no practical way to eliminate Armillaria from trees that are already colonized by the fungus. The useful life of an affected tree might be prolonged however, by supplemental watering during dry periods and appropriate fertilization to improve overall host condition. In very vigorous trees, the Armillaria fungi may be “walled off” and confined to just a portion of the root system or root collar. There are no chemical treatments that can effectively target Armillaria fungi within diseased trees.

How do I avoid Armillaria root disease in the future?

Practices that maintain trees in vigorous condition are the best means of preventing Armillaria root disease. Watering and fertilization to avoid stress will help trees resist infection. Because Armillaria root disease often develops in response to defoliation, suppression of both insect and leaf pathogen defoliators will indirectly reduce the occurrence and severity of Armillaria root disease. Because stumps and root systems of previously colonized trees can serve as “food bases” supporting rhizomorph growth for many years, thorough removal of stumps and root systems will reduce the risk of infection of other trees.

For more information on Armillaria root disease:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Ann Joy and Brian Hudelson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.