Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 02/29/2024
D-number:D0041
Anthracnose Hosts: Most trees, commonly ash, maple and oak Pathogens:Gloeosporium spp. as well as other fungi Signs/Symptoms: Blotchy dead areas on leaves For more information see: UW Plant Disease Facts D0002
Purple-Bordered Leaf Spot Host: Amur, Japanese, red, silver and sugar maple Pathogen:Phyllosticta minima Signs/Symptoms: Discrete, circular leaf spots with purple borders For more information see: UW Plant Disease Facts D0089
Tubakia (Actinopelte) Leaf Spot Hosts: Oak Pathogen:Tubakia spp. (Actinopelte spp.) Signs/Symptoms: Discrete circular, or irregular blotchy dead areas on leaves For more information see: UW Plant Disease Facts D0118
Apple Scab Hosts: Apple, crabapple, pear, mountain-ash Pathogen:Venturia inaequalis, V. pirina Signs/Symptoms: Circular, black leaf spots with feathery edges; eventual leaf loss For more information see: UW Plant Disease Facts D0004
Gymnosporangium Rusts Hosts: Apple, crabapple, hawthorn Pathogens: Gymnosporangium spp. Signs/Symptoms: Bright yellow-orange, circular leaf spots For more information see: UW Plant Disease Facts D0058
Powdery Mildew Hosts: Most deciduous trees Pathogens: Several genera of powdery mildew fungi Signs/Symptoms: Uniform/blotchy powdery white areas on upper and lower leaf surfaces For more information see: UW Plant Disease Facts D0087
Downy Leaf Spot Hosts: Hickory, walnut Pathogen:Microstroma juglandis Signs/Symptoms: Discrete powdery white areas on lower leaf surfaces
Chlorosis Hosts: Oak, red maple Cause: Iron or manganese deficiency, often induced by high soil pH Signs/Symptoms: Yellow leaves with dark green veins For more information see: UW Plant Disease Facts D0030
Scorch Hosts: Most deciduous trees Cause: Water stress induced by drought, high soil salt content, or other water-limiting factors Signs/Symptoms: Dead tissue on leaf margins
Tatters Hosts: Most deciduous trees, but commonly oak Cause: Possible early season cold injury Signs/Symptoms: Lacy, tattered-looking leaves For more information see: UW Plant Disease Facts D0111
For more information on deciduous tree leaf diseases:
See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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).
Thanks to Diana Alfuth, Kristin Krokowski, and Patti Nagai for reviewing this document, and to Matt Hanson for supplying the powdery mildew photo
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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 02/29/2024
D-number: D0033
Root and Crown Rots Hosts: All conifers Pathogens: Assorted root rot fungi/water molds Signs/Symptoms: Poor growth, branch dieback, discolored and deteriorated roots For more information see: UW Plant Disease Facts D0094
Rhizosphaera Needle Cast Hosts: Colorado blue spruce, other spruces Pathogen: Rhizosphaera kalkhoffii Signs/Symptoms: Browning/purpling of interior needles of lower branches, followed by needle drop For more information see: UW Plant Disease Facts D0093
Cytospora Canker Hosts: Colorado blue spruce, other spruces Pathogen: Cytospora kunzei Signs/Symptoms: Branch dieback with milky-white patches of dried sap on affected branches For more information see: UW Plant Disease Facts D0037
Spruce Needle Drop Hosts: Spruces Pathogen: Unknown (possibly Setomelannoma holmii) Signs/Symptoms: Needle loss and dieback at or near branch tips
Gymnosporangium Rusts Hosts: Juniper, apple, crabapple, hawthorn, quince Pathogen: Gymnosporangium spp. Signs/Symptoms: Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts) For more information see: UW Plant Disease Facts D0058
Phomopsis Tip Blight Hosts: Junipers Pathogen: Phomopsis juniperovora Signs/Symptoms: Browning and dieback of branch tips in spring and early summer as new growth emerges For more information see: UW Plant Disease Facts D0077
Diplodia Shoot Blight and Canker Hosts: Austrian pine, other pines Pathogen: Diplodia spp. Signs/Symptoms: Dieback of branch tips with dead needles showing uneven lengths For more information see: UW Plant Disease Facts D0042
Dothistroma Needle Blight Hosts: Austrian pine, other pines Pathogen: Dothistroma pini Signs/Symptoms: Needle tip browning and death with a distinct break between live and dead tissue For more information see: UW Plant Disease Facts D0043
Drought Stress Hosts: All conifers Cause: Insufficient water Signs/Symptoms: Purpling/browning of needles near branch tips or higher up in plants during the summer
Winter Injury/Winter Burn Hosts: All conifers, particularly yew and juniper Cause: Insufficient water Signs/Symptoms: Needle browning/bleaching over winter or in spring as plants come out of dormancy For more information see: UW Plant Disease Facts D0127
Herbicide Damage Hosts: All conifers Cause: Exposure to herbicides Signs/Symptoms: Twisted or otherwise distorted growth, needle yellowing or browning, plant death For more information see: UW Plant Disease Facts D0060
For more information on conifer diseases:
See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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).
Thanks to Ann Joy, Patti Nagai and Ann Wied for reviewing this document and to Bria Radtke for supplying the photo of spruce needle drop.
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.
Authors: Patricia McManus and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0076
What is peach leaf curl?
Peach leaf curl is a common disease of peach and nectarine trees throughout the Midwest and eastern U.S. Where the disease is severe, tree vigor and fruit quality and yield are reduced. Peach leaf curl often becomes more prevalent after relatively mild winters, which are more favorable for the survival of the organism that causes the disease. A related disease, plum pockets, affects plums.
Leaf distortions and discoloration typical of peach leaf curl.
What does peach leaf curl look like?
Diseased leaves are distorted with puckered, thickened, twisted areas that can be light green, yellow, or reddish to purple in color. Leaves later turn brown and fall from the tree. Diseased shoots are stunted with small, yellowish leaves, or have leaves arranged in tight whorls (rosettes). Diseased flowers may abort, leading to reduced fruit set, while diseased fruit are bumpy, reddish in color, and fall prematurely.
Where does peach leaf curl come from?
Peach leaf curl is caused by the fungus Taphrina deformans, which overwinters in bark and bud scales of peach and nectarine trees. Fungal spores infect leaves and shoots in the spring while leaves are still in the bud and as they just begin to emerge. Mild (50 to 70°F), wet weather during this period favors infection. Additional spores form on the surface of diseased tissue, and these spores cause new infections if the weather remains mild and wet.
How do I save trees that have peach leaf curl?
Peach leaf curl is unlikely to kill a peach or nectarine tree on its own. However, if significant premature leaf drop occurs, trees will be susceptible to drought stress and winter injury. To help maintain tree vigor, apply water (approximately one inch per week) at the drip lines (i.e., the edges of where the branches extend) of peach and nectarine trees during dry periods. Also, fertilize trees with nitrogen, but avoid fertilizing after August 1; late season fertilization will prevent trees from hardening off properly before winter, making them prone to winter injury. Finally, thin fruit if the crop load is heavy.
How do I avoid problems with peach leaf curl in the future?
Because Taphrina deformans survives in bark and bud scales, removing diseased leaves in the fall will not reduce disease. To prevent serious problems with peach leaf curl, plant resistant or tolerant peach varieties (e.g., ‘Frost’, ‘Indian Free’, ‘Q-1-8’, varieties derived from ‘Redhaven’). Avoid growing susceptible varieties (e.g., those derived from ‘Redskin’). In addition, consider applying a single fungicide spray in the fall after leaf drop or in the spring before buds begin to swell to control peach leaf curl (and also plum pockets). Effective fungicide active ingredients include chlorothalonil, copper (e.g., Bordeaux mixture), and ferbam. Choose a fungicide that is labeled for use on edible fruit crops, and read and follow all label instructions to ensure that you use the product in the safest and most effective manner possible.
For more information on peach leaf curl:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Patti Nagai, Teryl Roper, 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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 02/29/2024
D-number: D0042
Diplodia shoot blight and canker killing branch tips of Austrian pine.
What is Diplodia shoot blight and canker?
Diplodia shoot blight and canker (formerly Sphaeropsis shoot blight and canker) is one of the most common fungal diseases of Austrian pine in Wisconsin. This disease can also affect other pines including red, jack, Scots and mugo pine, as well as other conifers including cedars, cypresses, firs, junipers and spruces.
What does Diplodia shoot blight and canker look like?
Initially, affected branch tips may ooze a large amount of resin. Eventually, these branch tips brown and die, with dead needles on these branches having varying lengths. As the disease progresses, sunken or swollen, discolored areas (called cankers) may form on infected twigs. Diplodia shoot blight and canker can be distinguished from damage from boring insects (where there also may be heavy resin flow) by an absence of any tunneling.
Where does Diplodia shoot blight and canker come from?
Diplodia shoot blight and canker is caused by several fungi in the genus Diplodia. These fungi include Diplodia sapinea (formerly known as Diplodia pinea and Sphaeropsis sapinea), which has historically been cited as the cause of the disease on Austrian pine. However, this fungus is only one of several Diplodia species that can cause problems on this host. Diplodia fungi survive in infected shoots and pinecones where they form small, black fruiting bodies (i.e., reproductive structures) that produce brown-colored spores.
How do I save a tree with Diplodia shoot blight and canker?
Immediately remove and destroy diseased branch tips. Also, where possible, remove and destroy pinecones that have fallen from infected trees. Dispose of these materials by burning (where allowed by local ordinance) or burying them.
When pruning, cut branches six to eight inches below the point where they are obviously infected. Prune only in dry weather. Between cuts, decontaminate pruning tools by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants), or a 10% bleach solution (i.e., one part of a disinfecting bleach and nine parts water). Decontaminating tools is important to help prevent accidental movement of Diplodia fungi from branch to branch during pruning. If you decide to use bleach, be sure to rinse your tools thoroughly after pruning and then oil them to prevent rusting.
Needles of different lengths (left) and production of excessive resin on branch tips (right) are typical symptoms of Diplodia shoot blight and canker.
How do I avoid problems with Diplodia shoot blight and canker in the future?
Avoid planting Austrian pines; plant other types of evergreens instead. Minimize any stresses on established Austrian pines. Water trees adequately, particularly during dry periods. Established trees should receive approximately one inch of water per week from the time that the ground thaws in the spring, through the summer and into the fall up until the ground freezes or there is a significant snowfall. New transplants (i.e., conifers planted within three years) require approximately two inches of water per week. During periods with insufficient rain, apply water at the drip lines of trees (i.e., the edges of where the branches extend) using a drip or soaker hose.
When planting trees, be sure to allow ample space for roots to grow, avoid compacting the soil around trees, and make sure there is adequate soil drainage. Mulch trees to at least their drip lines with a high-quality mulch (e.g., shredded oak bark mulch, red cedar mulch). Use one to two inches on heavier (e.g., clay) soils. Use three to four inches on lighter (e.g., sandy) soils. Keep mulch approximately four inches from tree trunks. DO NOT fertilize new transplants, and fertilize established conifers only when a soil fertility test indicates that fertilization is needed. DO NOT overfertilize, particularly with nitrogen.
Finally, you may want to apply fungicides to help prevent infections. Apply fungicides only after you have pruned out diseased branches as described above. Fungicides prevent infections but do not cure existing infections. Alternate use of fungicides containing thiophanate-methyl and chlorothalonil that are labeled for use on conifers. Start applications at bud break and continue at 14 day intervals until full shoot elongation. DO NOT use thiophanate-methyl alone. Overuse of thiophanate-methyl can potentially select for variants of Diplodia that will no longer be controlled by this active ingredient. Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use the products in the safest and most effective manner possible.
For more information on Diplodia shoot blight and canker:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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, Jean Ferdinandsen, Jason Gough, Phil Luedtke, Scott Reuss 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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0093
Browning of interior spruce needles caused by Rhizosphaera needle blight.
What is Rhizosphaera needle cast?
Rhizosphaera needle cast is the most common disease of Colorado blue spruce in Wisconsin, making Colorado blue spruce unsightly and unusable in many landscape settings. The disease also affects other conifers including black, Engelmann, Serbian, Sitka, and white (e.g., Black Hills) spruce; Austrian, mugo and eastern white pine; Douglas-fir, balsam fir and western hemlock.
What does Rhizosphaera needle cast look like?
The first noticeable symptom of Rhizosphaera needle cast is purpling or browning and loss of the innermost needles on lower branches of spruce trees. Often, the youngest needles at the tips of branches remain healthy. Rows of small, black spheres form along the length of infected needles and are visible with a 10X hand lens. These black spheres are fruiting bodies (i.e., reproductive structures) of the fungus that causes the disease and are diagnostic.
Where does Rhizosphaera needle cast come from?
Rhizosphaera needle cast is typically caused by the fungus Rhizosphaera kalkhoffii, although other species of Rhizosphaera can be involved depending on the host. Infected needles, including those that are still attached to branches and those that have fallen to the ground, produce spores that can be blown or splashed to healthy needles.
How do I save a tree or shrub with Rhizosphaera needle cast?
Consider treating affected trees with fungicides labeled for use on evergreens and containing copper or chlorothalonil. Treatments will not cure existing infections, but can prevent additional infections. Apply treatments every three to four weeks starting as new needles emerge each spring. Continue applications through periods of wet weather. For fungicide treatments to be effective, thoroughly cover all needles. This may be difficult on large trees. 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.
How do I avoid problems with Rhizosphaera needle cast in the future?
The easiest way to avoid Rhizosphaera needle cast is to avoid planting Colorado blue spruce. If you do plant this tree, consider using dwarf varieties, and allow adequate spacing between trees so that branches will not overlap when they are full size. Dwarf varieties and properly spaced larger spruce varieties will have better air penetration and needles will dry more quickly. Dry needles are less likely to be infected. Check existing spruce trees for the disease, and remove and destroy any diseased branches and needles by burning (where allowed by local ordinance), burying or hot composting.
For more information on Rhizosphaera needle cast:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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, Jean Ferdinandsen, Lisa Johnson, Scott Reuss 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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0090
What is Ralstonia wilt?
Ralstonia wilt (also sometimes known as Southern wilt) is a typically lethal disease that affects over 250 plants in over 40 plant families. Susceptible greenhouse-grown ornamentals include, but are not limited to, plants in the genera Capsicum, Cosmos, Cyclamen, Dahlia, Fuschsia, Gerbera, Hydrangea, Impatiens, Lantana,Nasturtium and Pelargonium. Vegetables such as eggplant, pepper, potato and tomato, as well as tobacco, are also susceptible. Ralstonia wilt was first reported on geraniums (Pelargonium spp.) in Wisconsin in 1999. In 2020, the disease was reported on Fantasia® ‘Pink Flare’ geraniums in Michigan. Potentially infected ‘Pink Flare’ geraniums were also distributed to 38 other states including Wisconsin.
Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP
What does Ralstonia wilt look like?
Symptoms of Ralstonia wilt in geraniums are similar to those associated with bacterial blight (caused by Xanthomonas campestris pv. pelargonii). Initially, lower leaves of infected plants yellow and wilt, then die. Yellowing and death of upper leaves follow. Symptoms may initially occur on only one side of the plant. Internally, the water-conducting tissue of the plant browns, and then the entire stem rots from the inside out. Eventually, infected plants die.
Where does Ralstonia wilt come from?
Ralstonia wilt is caused by the bacterium Ralstonia solanacearum (formerly Pseudomonas solanacearum). This bacterium is commonly found in tropical, sub-tropical and warm temperate climates, but it is not believed to survive cold temperatures such as those typical of Wisconsin winters. The bacterium can be moved in symptomless plants or cuttings, or in contaminated soil and plant debris (where the pathogen can remain dormant for many years). Several subgroups (i.e., races and biovars) of R. solanacearum have been recognized, each with a different host range. R. solanacearum race 3, biovar 2 is of particular concern because it causes a serious disease of potato called brown rot. In addition, this race/biovar has been listed as a select agent by the U.S. government and is considered to have potential to be developed as a bioterrorist weapon against U.S. agriculture.
How do I save plants with Ralstonia wilt?
There are no known treatments that will save plants affected by Ralstonia wilt. If you believe your plants are suffering from this disease, immediately contact your local department of agriculture or county Extension agriculture or horticulture agent to arrange for confirmatory testing. If you live in Wisconsin, you can contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information) for assistance. If your plants test positive for R. solanacearum race 3, biovar 2 the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) must be notified and this organization will provide guidance on proper disposal of contaminated plants, as well as decontamination of greenhouses or other sites where contaminated plants have been grown.
How do I avoid problems with Ralstonia wilt in the future?
Start by purchasing and growing pathogen-free plant cuttings. Keep plants from different suppliers physically separated by at least four feet to minimize the risk of cross contamination should a shipment of plants prove to be contaminated. Because R. solanacearum is easily moved with soil or water, minimize splashing or any other movement of water or soil from plant to plant when watering. When taking cuttings or trimming plants, be sure to clean cutting tools between cuts using an approved disinfectant. For a complete list of such products, contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information). Also wear disposable gloves (nitrile are best) when handling plants, and change gloves between working with different geranium varieties. This will minimize the possibility of moving R. solanacearum by touch. If gloves are not available, wash your hands frequently and thoroughly (especially between geranium varieties) with lots of soap and water or with an alcohol-based hand sanitizer. Remove and destroy weeds or weed debris as these can harbor the pathogen. Finally, do not grow plants in a greenhouse where the disease has occurred unless it has been properly decontaminated.
For more information on Ralstonia wilt:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Alemu Mengistu, Julie Tans-Kersten and Laurie Weiss 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.
Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-number: D0103
The Southern blight fungus produces large numbers of spherical, light tan to dark red resting structures called sclerotia.
What is Southern blight?
Southern blight is a lethal fungal disease that is most common in the tropics and subtropics. This disease causes damage in the southern United States and can even cause problems in temperate locations like Wisconsin during periods of warm, moist weather. Southern blight has a wide host range, affecting over 500 plant species. Vegetable and fruit hosts include tomato, pepper, onion, beet, rhubarb, strawberry, lettuce, cucumber, melon, carrot, asparagus and parsley. Ornamental hosts include aster, black-eyed Susan, dahlia, daylily, gladiolus, hosta, impatiens, peony, petunia, rose, salvia, sedum and viola. Small woody trees and shrubs can be affected as well.
What does Southern blight look like?
Southern blight initially leads to a water-soaked appearance on lower leaves or water-soaked lesions (spots) on lower stems. Any plant part that is near or in contact with the soil may become infected. Infected plants yellow and wilt, often within days of infection, particularly when the weather is moist and warm (80 to 95°F). Fruit rots, crown rots and root rots are also typical symptoms of the disease. Thick mats of white fungal threads (called mycelia) may grow from infected tissue, radiating from the plant onto the soil surface. Sclerotia (small spherical structures that are about the size of mustard seeds) develop on infected tissue and on the soil surface. Sclerotia range in color from light tan to dark reddish-brown to black.
Where does Southern blight come from?
Southern blight is caused by the fungus Athelia rolfsii (formerly Sclerotium rolfsii), which lives in soil, on plants (including weeds), and in plant debris. The fungus can be spread through movement of infested soil and plant debris, on infected plants, in contaminated irrigation water, and through use of contaminated tools. In Wisconsin, A. rolfsii most likely enters gardens on infected nursery stock or infested mulch. Freezing temperatures will kill A. rolfsii mycelia, but sclerotia can survive temperatures as low as approximately 14ºF.
Southern blight can be a serious disease of vegetables, including tomatoes, leading to wilting and plant death. (Photo courtesy of Gary E. Vallad, University of Florida)
How can I save a plant with Southern blight?
Identify the extent of an infestation based on visible dead/dying plants, fungal mycelia and sclerotia. Remove all plants (including roots), as well as three inches of soil, from at least 12 inches beyond the infested area. Start at the edge of the infested area and work toward the center. Bag all plants and soil and dispose of these materials in a landfill. Turn any remaining soil in the infested area eight to 12 inches to bury any sclerotia that you may have missed. This will reduce the length of time that the sclerotia will survive. Grow non-susceptible plants (e.g., larger woody ornamentals) in the affected area for two to three years to allow time for sclerotia to die naturally. Fungicides containing azoles (e.g., propiconazole, tebuconazole), fludioxonil, flutolanil, mancozeb, PCNB, strobilurins (e.g., azoxystrobin, fluoxastrobin), thiophanate-methyl, and triadimefon are all labeled for Southern blight control, but may have varying levels of effectiveness. All of these products will likely be more effective if applied as preventive treatments rather than in an attempt to “cure” existing disease. If you decide to use fungicides, DO NOT use one active ingredient for all treatments. Instead, alternate the use of two or more unrelated active ingredients to help minimize problems with fungicide-resistant strains of A. rolfsii. DO NOT alternate active ingredients that are chemically related (e.g., propiconazole and tebuconazole, or azoxystrobin and fluoxastrobin). Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.
How can I prevent Southern blight in the future?
Inspect new plants for sclerotia and mycelia of A. rolfsii prior to transplanting. Bag and dispose of diseased plants as described above. Use high-quality mulches (e.g., shredded oak bark mulch, red cedar mulch) in your garden and avoid any mulches that you suspect might be contaminated with A. rolfsii. A. rolfsii thrives under moist conditions. Therefore, thin existing gardens or space plants farther apart in new gardens to improve airflow and promote more rapid drying of foliage and soil.
For more information on Southern blight:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Lynn Adams, Bryan Jensen, Mark Kopecky, Kaitlyn Lance, Mike Maddox, and Ann Wied for reviewing this document. Thanks also to Mike Maddox for supplying the photo.
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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-number: D0110
What is tar spot?
Tar spot is a common, visually distinctive and primarily cosmetic fungal leaf spot disease. Tar spot can affect many species of maple, including (but not limited to) silver maple, sugar maple and Norway maple. Boxelder (also known as ash-leaved maple), willow, holly and tulip-tree can also be affected by tar spot.
Symptoms of tar spot of silver maple caused by Rhytisma americanum (left) and tar spot of Norway maple caused by Rhytisma acerinum (right).
What does tar spot look like?
Initial symptoms of tar spot are small (approximately 1/8 inch) yellowish spots that form on infected leaves. These spots may remain relatively small, or may enlarge over the growing season to approximately 3/4 inch in diameter. As tar spot develops, black structures (resembling blobs of tar) form. On Norway maple, the black structures are typically numerous, small (approximately 1/8 inch in diameter), and clustered together. On silver maple, the black structures are often single, large (approximately 3/4 inch in diameter) and visibly raised. If you carefully examine the larger tar-like areas on silver maple, you will see convoluted line patterns that resemble fingerprints.
Where does tar spot come from?
Several fungi in the genus Rhytisma cause tar spot. On maples specifically, Rhytisma americanum, Rhytisma acerinum, and (less commonly) Rhytisma punctatum cause tar spot. Tar spot fungi commonly survive in leaf litter where they produce spores in the spring that lead to leaf infections.
How do I save a tree or shrub with tar spot?
DO NOT panic. For most maples and other susceptible trees and shrubs, tar spot is not a serious disease. It is a cosmetic disease that makes trees and shrubs look unsightly. Tar spot does not kill trees or shrubs, nor does it typically even cause serious defoliation.
How do I avoid problems with tar spot in the future?
You can reduce or even eliminate tar spot by simply collecting up and properly disposing of leaves from affected trees and shrubs each fall. These leaves can be burned (where allowed), buried or hot composted. When composting, make sure that your compost pile reaches a high temperature (approximately 140°F). Also, make sure that you routinely turn your compost pile 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 tar spot fungi.
Fungicides containing copper, alone or in combination with mancozeb, are labeled for tar spot control in Wisconsin. However, fungicide treatments for this disease are rarely, if ever, warranted. Consult with your county Extension horticulture/agriculture agent to determine if your tree warrants preventative treatments. If warranted, three fungicide applications will be needed: 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 ensure that you use the product in the safest and most effective manner possible.
For more information on tar spot of trees and shrubs:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Lis Friemoth, Ann Joy 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.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 02/28/2024
D-number: D0004
What is apple scab?
Apple scab is a potentially serious fungal disease of ornamental and fruit trees in the rose family. Trees that are most commonly and severely affected include crabapple, hawthorn, mountain-ash, apple and pear. In ornamental trees, leaf loss caused by apple scab can make trees unsightly and aesthetically unappealing. In fruit trees, leaf loss can reduce fruit yield. In addition, the presence of apple scab on fruits can make the fruit difficult, if not impossible, to market.
Leaf spots typical of apple scab on apple. Typical apple scab leaf spots (left) and fruit lesions (right). The disease can cause total defoliation and make fruit unmarketable.
What does apple scab look like?
Apple scab lesions (diseased areas) are often first noticed on leaves, where they most commonly occur on the upper leaf surface. Fruits are also very susceptible to infection. Lesions on both leaves and fruits are roughly circular with feathery edges and have an olive green to black color. Lesions can be as small as the size of a pinhead or as large a ½ inch in diameter. When disease is severe, lesions can merge and cover a large portion of the leaf or fruit surface. Defoliation of a tree (i.e., extensive leaf drop) often follows.
Where does apple scab come from?
Scab is caused primarily by the fungus Venturia inaequalis. Other species of Venturia can be involved in diseases similar to apple scab. In particular, Venturia pirina causes a very similar disease (called pear scab) on pear. Venturia inaequalis and its relatives survive the winter in leaf litter from infected trees. Scab is most severe in cool, wet years.
How do I save a tree with apple scab?
Apple scab is not a lethal disease, even when trees totally defoliate. Once symptoms are visible, it is too late to treat a tree. Proper long-term management of apple scab is important however. If left unchecked, defoliation due to apple scab year after year can stress a tree and make it more susceptible to other, more serious and lethal diseases and insect pests.
How do I avoid problems with apple scab in the future?
If your crabapple, apple or pear tree has a history of severe scab, consider replacing it with a resistant variety. See UW Bulletins A2105 (Apple Cultivars for Wisconsin), A2488 (Home Fruit Cultivars for Northern Wisconsin), and A2582 (Home Fruit Cultivars for Southern Wisconsin) for recommendations. These publications are all available at https://learningstore.extension.wisc.edu/.
If you have a susceptible tree that you want to maintain, carefully collect up and discard fallen, infected leaves each autumn. These leaves are a major source of spores that can infect leaves the following growing season. Also, be sure to routinely thin your trees to open up the canopy and allow better airflow. Thinning will promote more rapid drying of leaves, which is less favorable for apple scab development.
Even with proper fall leaf clean up and thinning, you may have to consider applying fungicide treatments to susceptible trees, particularly when the weather is cool and wet. Captan, chlorothalonil, mancozeb, myclobutanil, propiconazole, or thiophanate methyl, are available for apple scab control, although not all of these active ingredients can be used on trees where fruit will eventually be eaten. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the correct fungicide(s) in the safest and most effective manner possible. Typically, you will need to treat every seven to 14 days from bud break until wet weather subsides. DO NOT use myclobutanil, propiconazole, or thiophanate methyl as the sole active ingredient for all treatments. If you decide to use one of these active ingredients, alternate its use with at least one of the other active ingredients listed above to help minimize problems with fungicide-resistant strains of the apple and pear scab fungi.
For more information on apple scab:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Paul Hartman, Laura Jull, Patti Nagai and Scott Reuss 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.
Eastern filbert blight is a potentially serious fungal disease found throughout the United States, including Wisconsin. It affects only Corylus species, commonly known as hazelnuts or filberts. On hazelnuts native to Wisconsin such as American hazelnut (Corylus americana) and beaked hazelnut (Corylus cornuta), the disease causes little significant damage, but on the commonly grown European hazelnut (Corylus avellana), including Harry Lauder’s walking stick (Corylus avellana ‘Contorta’), the disease is lethal. Turkish filbert (Corylus colurna) also appears to be highly susceptible.
Eastern filbert blight can cause small black cankers that form in rows, or deep gouges in the bark of severely infected trees/shrubs.
What does Eastern filbert blight look like?
Eastern filbert blight causes cankers (i.e., dead, collapsed areas) on branches or main trunks. Easily visible within the cankers are black, football-shaped stromata (the reproductive structures of the causal fungus). The stromata often form in rows of two. Cankers first appear on new twigs and expand over time. American hazelnut trees/shrubs are able to live almost indefinitely with Eastern filbert blight, forming a small number of slowly-expanding cankers (if any cankers form at all) that lead to limited branch dieback. On European hazelnut however, cankers will expand anywhere from one inch to three feet in a year, and can eventually form long, deep gouges or grooves on severely affected trees/shrubs. European hazelnuts typically die due to girdling from Eastern filbert blight within five to 10 years of initial infection.
Where does Eastern filbert blight come from?
Eastern filbert blight is caused by the fungus Anisogramma anomala.Stromata formed by the fungus produce spores that are spread short distances by water splash and over longer distances by wind. Humans also can spread Anisogramma anomala on their hands and clothing, on gardening tools, and by transporting wood from infected trees/shrubs. Unlike other canker fungi that infect through wounds, the Eastern filbert blight fungus primarily infects through immature tissue on actively growing shoots. Cankers appear 12 to 18 months after infection. Eastern filbert blight does not affect hazelnut leaves, fruits or nuts.
How do I save trees/shrubs with Eastern filbert blight?
There is no cure for Eastern filbert blight. If only a few branches on a tree/shrub are affected, prune these branches two to three feet below each canker. Decontaminate tools after each cut by treating them for at least 30 seconds with a 10% bleach solution or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).
If a tree/shrub is severely affected by Eastern filbert blight (e.g., when there are so many cankers on multiple branches that the tree/shrub would look ugly if pruned, when branch pruning would require removing part of the trunk, or when trunk cankers are present), removal of the tree/shrub is the preferred management strategy.
Pruned branches and removed trees/shrubs should be burned (where allowed by local ordinance), deep-buried, or chipped (as long as the chips are allowed to dry to kill the Eastern filbert blight fungus).
How do I avoid problems with Eastern filbert blight in the future?
Consider planting native species of hazelnut (e.g., American and beaked hazelnut) that are naturally resistant to the disease. If you decide to plant European hazelnut, select cultivars that have been bred for resistance. ‘Jefferson’, ‘Santiam’, ‘Yamhill’, and ‘Theta’ are resistant, nut-bearing cultivars. ‘Red Dragon’ is a resistant, ornamental cultivar. Note that these cultivars are not hardy in all hardiness zones in Wisconsin. Hybrid hazelnuts (crosses between American and European hazelnut) are becoming increasingly available, but should be used with caution because their susceptibility to Eastern filbert blight has not been adequately tested.
Once hazelnut trees/shrubs are established in your yard, routinely inspect the plants for infection and remove infected branches as they occur. Watch for dying branches in the summer and cankers (particularly on or near the youngest growth) in the winter. Inspecting trees during the winter is very important, because cankers are more visible at that time.
Fungicides can be used for management, but should only be used as a last resort. Not all fungicides that are approved for Eastern filbert blight control are particularly effective, but chlorothalonil has been shown to be an effective preventative treatment, although it will not cure existing infections. Note that not all formulations of chlorothalonil are approved for use on nut-bearing hazelnuts; many formulations can only be used on ornamental hazelnuts. Therefore, if you decide to use chlorothalonil, be sure to select the appropriate formulation for your particular situation. Apply the first treatment at bud break (i.e., when half the buds show a separation of leaves) and additional treatments (up to three) every two weeks thereafter. If you plan to eat nuts from your hazelnut tree, make sure that your last fungicide treatment is applied at least 120 days before anticipated nut harvest. For further details about recommended fungicides, spray rate recommendations, and diagrams of bud stages, see Pest Management Guide for Hazelnuts in the Willamette Valley, Oregon State University Extension Bulletin EM8328 available at https://catalog.extension.oregonstate.edu/em8328.
For more information on Eastern filbert blight:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Jason Fischbach, Benjamin Gold, Laura Jull, Marian Lund, Ryan Morey, and Mary Pelzer 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.
