All posts by hudelson

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop

Bacterial Canker

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Mary Francis Heimann* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0009

What is bacterial canker?

Bacterial canker is a common and sometimes lethal disease of trees in the genus Prunus including cherry, plum and peach. Bacterial canker is sometimes also referred to as “gummosis”, “blossom blast”, “dieback”, “spur blight” and “twig blight”.

Ooze (see arrow) on Prunus branches or trunks can indicate a bacterial canker problem.

What does bacterial canker look like?

Often branch dieback is the first symptom of bacterial canker that homeowners notice. However, other more subtle symptoms of flowers, leaves, fruits and branches typically precede this dieback. Initially, infected trees are symptomless. Infected flowers often open but then collapse. Infected leaves become spotted and yellowed. The centers of leaf spots often shothole (i.e., fall out). If spotting is severe, leaves may fall off. Infected fruits develop dead spots surrounded by water-soaked tissue. Spots can eventually develop into a fruit rot. Branch or trunk infections often occur at pruning sites and lead to cankers (i.e., sunken, dead areas). Cankers often produce a gummy, resinous ooze. Wood in the cankered area is typically discolored. Flower, fruit and branch infections can become systemic, leading to twig dieback, death of larger branches, or even death of an entire tree.

Where does bacterial canker come from?

Bacterial canker is caused by the bacteria Pseudomonas syringae pv. syringae (Pss) and P. syringae pv. mors-prunorum (Psm). These bacteria overwinter in cankers, in asymptomatic, systemically infected branches, and in buds of susceptible trees. Pss is also known to occur naturally on the leaves of many plants including many weed species. Both Pss and Psm can subsequently be spread by rain splash, wind, or insects. The bacteria can also be spread to healthy branches when contaminated pruning tools are used. Infections most often occur during cool, wet conditions.

How do I save a plant with bacterial canker?

Prune infected branches at least 12 inches below cankers or other dead tissue, and dispose of branches by burning (where allowed by local ordinance) or burying them. Prune branches only during the winter (e.g., Jan. and Feb.) or during dry periods in late summer (e.g., Aug.). DO NOT prune during the cool, wet periods (e.g., spring and fall). Disinfest pruning tools after each cut by treating them for at least 30 seconds with a 10% bleach solution or preferably 70% alcohol (e.g., rubbing alcohol straight from the bottle or a spray disinfectant). If you decide to use bleach, be sure to thoroughly rinse and oil your tools after pruning is complete to prevent rusting.

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

Healthy trees are better able to slow the development of bacterial canker. Therefore make sure that trees are watered and fertilized properly. Keep weeds and other plants that may harbor bacterial canker pathogens from around the base of susceptible trees. Copper-containing sprays have been advocated for bacterial canker management. However, in many areas, copper-resistant strains of Pss and Psm are present and therefore copper sprays are ineffective.

For more information on bacterial 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

*Mary Francis Heimann is a Distinguished Outreach Specialist Emerita at the University of Wisconsin-Madison.

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 Diana Alfuth, Patty McManus 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

Bacterial Blight

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Gina Foreman* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0008

Death of lilac branch tips and leaves due to bacterial blight.

What is bacterial blight?

Bacterial blight, also known as blossom blight or shoot blight, is a common and often serious disease of Chinese, Japanese, Persian and common lilac, as well as walnut, apple, pear, plum and cherry. White flowering varieties of common lilac are most susceptible to the disease.

What does bacterial blight look like?

Initial symptoms of bacterial blight may include dark brown necrotic (dead) leaf spots with yellow halos. If leaf spots develop before leaves are fully expanded, leaf curling and twisting may result. More advanced symptoms include necrotic blotches starting at the leaf margins and advancing inward, as well as black streaking on twigs. In its most severe form, bacterial blight can result in the death of branch tips, leaves and blossoms.

Where does bacterial blight come from?

Bacterial blight is caused by the bacterium Pseudomonas syringae pv. syringae (Pss), which survives in diseased stem tissue (cankers), plant debris, and soil. Pss can be spread by insects and on pruning tools but is more commonly spread by wind and rain. Often Pss is found on the surface of healthy plants and does not cause disease. Infections can occur when the bacterium enters tissue through natural openings or through wounds caused by insects, pruning, wind damage or hail.

How do I save a plant with bacterial blight?

Prune diseased twigs 10 to 12 inches below the point of visible symptoms, and dispose of the branches by burning (where allowed by local ordinance) or burying them. Always prune in dry weather, and disinfest pruning tools after each cut by treating them for at least 30 seconds with a 10% bleach solution or preferably 70% alcohol (e.g., rubbing alcohol straight from the bottle or a spray disinfectant). If you decide to use bleach, be sure to thoroughly rinse and oil your tools after pruning is complete to prevent rusting.

How do I avoid problems with bacterial blight in the future?

When planting lilacs, provide adequate spacing between shrubs. Thin individual shrubs each winter to promote good air circulation (see University of Wisconsin Garden Facts XHT1015, Pruning Deciduous Shrubs, for pruning tips). Properly water, fertilize and mulch shrubs to avoid stress that may predispose them to disease. Avoid overhead watering that may keep leaves wet. If you have had chronic problems with bacterial blight, you may want to use a combination of copper and mancozeb-containing fungicides for control. Apply fungicides two to three times at seven to 10 day intervals as leaves emerge, but before symptoms develop. 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.

For more information on bacterial 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 Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison.

Thanks to Ann Joy, Kristin Kleeberger and Mike Maddox 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 - Herbaceous Ornamental, Disease - Vegetable

Aster Yellows

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0007

What is aster yellows?

Aster yellows is a chronic, systemic disease that affects over 300 species of broad-leafed, herbaceous plants in at least 38 families. Members of the aster family (Asteraceae), such as asters, marigolds, Coreopsis and purple coneflower are commonly affected by this disease. Vegetable crops such as carrots and potatoes are also susceptible. Aster yellows occurs throughout North America.

Coneflowers with aster yellows (right) often have deformed, discolored flowers.

What does aster yellows look like?

Infected plants are typically stunted and twisted, with foliage that is yellow, purple or red. Infected plants are often sterile. Floral parts that are normally brightly colored may be green, and petals and sepals may become puckered and distorted. In purple coneflower, secondary flower heads (often in a cluster) may emerge from the primary flower head. In marigolds, flowers are often leafy and a muddy green-orange color. Infected carrots have purple/red leaves and form taproots with tufts of small, white “hairy” roots. Tap roots from infected carrots often have a bitter taste.

Where does aster yellows come from?

Aster yellows is caused by the aster yellows phytoplasma, a bacterium-like organism that lives in the food-conducting tissue (phloem) of plants. Aster yellows is rarely lethal. Thus, infected perennials can serve as a source of the aster yellows phytoplasma for many years. The aster leafhopper (Macrosteles fascifrons), a common insect, moves the aster yellows phytoplasma from plant to plant.

How do I save a plant with aster yellows?

There is no known cure for aster yellows. Plants suspected of having aster yellows, including weeds such as dandelions, should be removed immediately so that the aster yellows phytoplasma cannot be spread from infected plants to other non-infected plants in the area. Proper diagnosis of aster yellows is important because management of herbicide and eriophyid mite damaged plants does not require plant removal.

How do I avoid problems with aster yellows in the future?

Some herbaceous plants (e.g., geraniums and impatiens), as well as most woody ornamentals, are not susceptible to aster yellows. Therefore these plants should be used in areas where aster yellows is a problem. In landscape settings, attempts to control aster leafhoppers as a means of controlling aster yellows are typically not effective and are not recommended.

For more information on aster yellows:

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, Ann Joy 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

Ash Yellows

July 6, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/28/2024

D-number: D0006

What is ash yellows?

Ash yellows is a chronic, systemic disease that affects ash trees of all ages. White ash is particularly susceptible to ash yellows. Ash yellows likely occurs wherever ash is grown and has been reported widely in the United States and southern Canada. The organism that causes ash yellows also causes a disease called lilac witches’-broom.

Brooming symptoms in an ash tree caused by ash yellows.

What does ash yellows look like?

Symptoms of ash yellows usually occur within three years of infection. Infected trees typically grow at a much slower rate than non-infected trees, although this may be difficult to detect in an isolated, single tree. The rate of growth of an infected tree may be as little as one half that of a healthy tree. Leaves on infected trees are frequently smaller, thinner and lighter green than normal. Often, but not always, affected trees will produce branches in tufts, a symptom that is called “brooming”. Eventually, branches in the crown will die and this dieback can continue until the entire crown is dead.

Where does ash yellows come from?

Ash yellows is caused by the phytoplasma, Candidatus Phytoplasma fraxini. Phytoplasmas are bacteria-like organisms that live and survive in the phloem (the food-conducting tissue) of infected plants. Leafhoppers are thought to be the primary means by which this pathogen is moved from tree to tree.

How do I save a tree with ash yellows?

There is no known cure for ash yellows, but some infected trees may live and grow slowly with the disease for many years. Ash trees suspected of having ash yellows should be tested for the disease, and those trees that test positive should be removed immediately to prevent spread of the ash yellows phytoplasma to other trees in the area. Wood harvested from infected trees does not serve as a source of the phytoplasma and can be used for woodworking or firewood, or chipped for mulch.

How do I avoid problems with ash yellows in the future?

Avoid growing ash trees in areas where ash yellows is prevalent. When choosing a lilac, select a variety of common lilac as these varieties appear to have tolerance to the ash yellows phytoplasma. Avoid using S. josikaea, S. reticulata and S. sweginzowii (or hybrids of these species with either S. komarowii or S. villosa), as these lilacs appear to be highly susceptible. It is unclear if the use of insecticides (or other means) to control leafhoppers can help control the spread of this pathogen.

For more information on ash yellows and ash yellows testing:

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 Lis Friemoth, Ann Joy 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/.

Disease - Field and Forage

Aphanomyces Root Rot of Alfalfa

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Quinn Watson and Damon Smith, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0003

Stunting and yellowing of alfalfa plants (leading to increased weed pressure) is typical of Aphanomyces seedling blight and root rot. (Photo courtesy of Craig Grau)

What is Aphanomyces root rot of alfalfa?

Aphanomyces root rot (ARR) is a serious disease of both recently seeded alfalfa and established alfalfa stands. ARR can cause severe yield reductions in affected alfalfa fields. Variations of the disease also occur on many other legumes (including soybean, snap bean, faba bean, red kidney bean, pea, red clover, and white clover) and can cause significant losses in these crops as well.

What does Aphanomyces root rot look like?

Typically, alfalfa emergence is not dramatically affected by ARR, but symptoms appear shortly after seedlings emerge. Young plants appear stunted and yellow and may eventually die. The root systems of affected seedlings are smaller than normal, and what roots remain appear gray and water-soaked. Older alfalfa plants suffering from ARR also tend to be stunted and yellow. They may have a well-developed tap root but typically relatively few smaller, fine roots. Often, growers realize they have a problem with ARR when they notice that weeds in their fields are growing more vigorously than their alfalfa crop.

Where does Aphanomyces root rot come from?

ARR is caused by the soilborne water mold (i.e., fungus-like organism) Aphanomyces euteiches. A. euteiches is commonly found in fields that are poorly drained, fields with heavier (i.e., clay) soils, fields with compaction, and fields that receive excessive water. A. euteiches produces microscopic, long-lived resting spores (called oospores) in the roots of infected plants, and these spores can remain dormant in the soil for up to 10 years, even in the absence of a susceptible crop. Once a susceptible crop is present, oospores can germinate and directly infect plants, or under wetter conditions produce numerous microscopic swimming spores (called zoospores) that can subsequently infect plants.

There are several variants of A. euteiches and these variants tend to have preferences for which plant hosts they will infect. For example, some variants tend to infect alfalfa, others tend to infect peas and others tend to infect snap beans. A. euteiches that infects alfalfa can be further divided into two races (race 1 and race 2), which can be distinguished based on the particular alfalfa varieties that they most readily infect. Other races of A. euteiches that can infect alfalfa likely exist, but at this time have not been fully documented.

Alfalfa plants with Aphanomyces seedling blight/root rot have reduced numbers of small, fineroots. (Photo courtesy of Craig Grau)

How can I save plants with Aphanomyces root rot?

There is no way to save an alfalfa crop once ARR has occurred. Fungicide seed treatments may provide short-term protection of alfalfa seedlings. However, foliar fungicides do not provide any ARR control.

How can I avoid problems with Aphanomyces root rot in the future?

The most important management strategy for ARR is to make sure fields are properly drained. Reducing standing water is important to prevent development of zoospores, which can dramatically increase disease severity. Reducing compaction, using sub-surface drainage tiles and/or re-routing surface water drainage pathways can help alleviate wet soil conditions. If there is a past history of ARR in a field, use alfalfa varieties with resistance to the specific race(s) of A. euteiches present in the field. Which race(s) are present can be determined using a soil bioassay. Contact your local county Extension office for more information on how to collect a soil sample for A. euteiches testing, as well as for recommendations on appropriate alfalfa varieties to use once the results of the soil bioassay are available. In some areas of Wisconsin (such the southwest), both race 1 and race 2 of A. euteiches are widespread. Therefore, routine use of alfalfa varieties resistant to both races may be warranted. Crop rotation is not an effective management strategy for ARR because oospores of A. euteiches survive for long periods in the soil. Alfalfa seed treatments may provide protection to seedlings only up until shortly after emergence. Foliar fungicides, fumigants and other biological control products are also not effective in managing ARR.

For more information on Aphanomyces root rot:

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 Ted Bay, Bryan Jensen and Craig Saxe 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 agriculture-related questions at https://extension.wisc.edu/agriculture/ask-an-agriculture-question/.

Disease - Broad Leafed Woody Ornamental

Anthracnose

June 30, 2015 hudelson

UW Plant Disease Facts

Anthracnose is very common on many types of trees and shrubs. It often occurs on the leaves of ash (left) and maple (right) trees, causing blotchy-brown, dead areas.

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0002

What is anthracnose?

Anthracnose is the name of several common fungal diseases that affect the foliage of woody ornamentals in Wisconsin. Trees that are most commonly and severely affected by anthracnose include ash, maple, white oak, sycamore, and walnut. Anthracnose typically affects young leaf tissue.

What does anthracnose look like?

Symptoms of anthracnose vary from host to host, but in general include irregular spots, and dead areas on leaves that often follow the veins of the leaves. Affected tissue can vary in color but is often tan or brown. Severely affected leaves often curl and may fall off. In some tree species, such as sycamore, twigs can also become infected leading to twig dieback.

Where does anthracnose come from?

Anthracnose is caused by several fungi (many historically classified in the genus Gloeosporium) that survive in leaf litter. These fungi are host specific. The anthracnose fungus that infects one type of tree (e.g., ash) is not the same one that infects another type of tree (e.g., maple). However, when anthracnose occurs on one tree, then weather conditions (typically cool and moist conditions) are favorable for development of the disease on many types of trees.

Anthracnose can be severe on some hosts. On white oak (left), it can cause extensive leaf browning and curling. On sycamore (right), anthracnose can cause twig dieback.

How do I save a tree with anthracnose?

DO NOT panic. For many trees, anthracnose is a cosmetic disease. It may make a tree look a little ragged but will not kill the tree. However, if a tree has been defoliated by anthracnose for several years, or it is a tree, such as a sycamore, where twig infections can occur, then you may want to use a fungicide for disease control. Three treatments are typically needed for adequate control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded. Fungicides containing copper, chlorothalonil, or mancozeb are registered for anthracnose control in Wisconsin. DO NOT use the same active ingredient for all treatments. Instead, alternate the use of at least two active ingredients to help minimize problems with fungicide-resistant strains of anthracnose fungi. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the fungicide(s) in the safest and most effective manner possible.

How do I avoid problems with anthracnose in the future?

You can reduce the number of spores that cause anthracnose infections by removing and disposing of fallen, infected leaves in the autumn. Leaves can be burned (where allowed), buried 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 anthracnose fungi. 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 anthracnose:

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 Laura Jull, Patti Nagai and Amy Sausen 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 - Fruit Crop

Angular Leaf Spot of Strawberry

June 30, 2015 hudelson

UW Plant Disease Facts

Authors: Isael Rubio*, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0001

What is angular leaf spot?

Angular leaf spot is a severe bacterial disease that can adversely affect strawberries wherever they are grown, potentially causing yield losses of up to 75%. The disease appears to have originated in the U.S and was first described in Minnesota in 1960.

What does angular leaf spot look like?

Symptoms of angular leaf spot develop on strawberry leaves and sepals (the green leaf-like parts of the strawberry fruit). Initial symptoms are small, angular (i.e., straight-edged), water-soaked, translucent spots on lower leaf surfaces. White, cream or yellow-colored ooze may appear on the spots when humidity is high. This ooze can eventually dry and become crusty. As the disease progresses, spots enlarge and merge, becoming visible on the upper surfaces of the leaves. Severely affected leaves dry and turn reddish-brown. Parts of the leaves can tear away. Angular leaf spot can also cause sepals to darken, leading to so-called “black caps” that reduce the quality and salability of fruit.

Straight-edged spots on strawberry leaves with oozy masses in the center are typical of angular leaf spot. (Photo courtesy of Patricia McManus)

Where does angular leaf spot come from?

Angular leaf spot is caused by the bacterium Xanthamonas fragariae which is typically introduced into a garden on infected plants. Once present in a garden, the bacterium can be spread by splashing water from rain or watering with a sprinkler. Once established in a garden, X. fragariae overwinters on strawberry leaf debris. Weather conditions that favor angular leaf spot are not well understood, although high humidity appears to play a role.

How do I save a plant with angular leaf spot?

Once a plant is infected, it cannot be cured. If angular leaf spot is detected early, use of copper-containing compounds labeled for use on strawberries may help limit disease development although the effectiveness of such sprays can be quite variable. If you decide to use such a product, be sure to read and follow all label instructions for the product that you select to ensure that you use it in the safest and most effective manner possible. Avoid using copper sprays once flowers have formed.

How do I avoid problems with angular leaf spot in the future?

Unfortunately, strawberry cultivars resistant to angular leaf spot are not available and some cultivars (e.g., ‘All Star’, ‘Annapolis’, ‘Cavendish’, ‘Honeoye’ and ‘Kent’) have been observed to develop particularly severe symptoms. When first establishing a strawberry patch, be sure to purchase disease-free plants. When watering, use a drip or soaker hose to reduce splash that can move X. fragariae from plant to plant. Also, DO NOT handle strawberry plants or harvest berries when they are wet, as this can promote spread of the pathogen. Prevent additional spread on gardening tools and other gardening items by dipping or treating them for at least 30 seconds with 10% bleach or preferably (because of its less corrosive properties) 70% alcohol. Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol and are easy to use. If angular leaf spot occurs in your strawberry patch, remove infected leaves and any infested debris. Dispose of this material by burning (if allowed by local ordinance) or burying it.

For more information on angular leaf spot of strawberry:

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 Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Diana Alfuth, Ricardo Garcia, Kristin Krokowski, Jenna Lind , Toby Lunt, Patricia McManus, Yoana Mendoza and Jaime Trejo 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/.