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:
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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson UW-Madison Plant Pathology
Last Revised: 02/29/2024
D-number: D0049
What is elderberry rust?
Elderberry rust is a visually striking fungal disease that affects stems, leaves and flowers of plants in the genus Sambucus (i.e., elderberries). The disease also affects sedges (Carex spp.). On elderberries grown as ornamentals, as well as on sedges, the disease is primarily a cosmetic problem. However, if elderberries are grown for fruit, the disease can disrupt flower and fruit formation, thus reducing fruit yield.
An elderberry rust gall on elderberry (left) and leaf spots caused by elderberry rust on sedge (right). Photos courtesy of Jenell Bindl (left) and Michele Warmund, University of Missouri (right)
What does elderberry rust look like?
Elderberry rust is most noticeable on elderberries where it causes growth distortions and swellings (i.e., galls) on leaves and stems. Galls are often very large, bright yellow and powdery from spores produced by the causal fungus. In extreme cases, galls can resemble banana slugs that have attached themselves to branches. Infected flowers become thick, swollen and green-tinged rather than white. Affected plant parts are covered with a network of small (approximately 1/16 inch in diameter) ring-like spots. These spots are reproductive structures of the rust fungus and produce the powdery spores that coat the galls.
On sedges, elderberry rust causes brownish leaf spots, often with yellow halos. The spots eventually erupt releasing powdery, rusty-orange spores.
Where does elderberry rust come from?
Elderberry rust is caused by the fungus Puccinia sambuci, also known as Puccinia bolleyana. The fungus overwinters in sedge debris, and spores produced in this debris blow to elderberry plants in the spring, leading to infection and gall formation. Spores produced in elderberry galls blow back to sedges, where infection of newly produced leaves (and other plant parts) occurs. These infections lead to spotting and to the formation of a third type of spore that reinfects sedges causing additional spotting. Late in the season a fourth type of spore is produced that serves as the overwintering phase of the fungus. Infection of both elderberries and sedges is favored by wet weather.
How do I save plants with elderberry rust?
Elderberry rust is not a lethal disease on either elderberry or sedge. When galls form on elderberry, simply prune these out. This will make elderberry plants more aesthetically pleasing and limit spread of the fungus to sedges. When pruning, cut branches four to six inches below each gall. Between cuts, decontaminate pruning tools by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), a spray disinfectant containing 60-70% active ingredient, or a 10% bleach solution (i.e., one part of a disinfecting bleach and nine parts water). If you decide to use bleach, be sure to rinse your tools thoroughly after you are done pruning and then oil them to prevent rusting, which can be caused by bleach use. Dispose of galls by burning (where allowed by local ordinance) or burying them.
How do I avoid problems with elderberry rust in the future?
In landscape settings, the best way to avoid problems with elderberry rust is to remove any sedges that are growing near elderberry plants. The farther the distance between elderberries and sedges, the less likely that elderberry rust will be an issue. Also, increase airflow around elderberry plants by thinning them and removing surrounding plants. Increased airflow will dry plants more rapidly and make the environment less favorable for infection. DO NOT use a sprinkler to water plants, as that wets leaves and provides a better environment for infections to occur. Instead, use a soaker or drip hose to apply supplemental water to the soil at the drip lines of the plants (i.e., the edges of where the branches extend). While fungicides are available for rust control in commercial elderberry production, these products are not recommended for use in home garden settings.
For more information on elderberry rust:
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 Katherine Amann, Kaitlyn Davis, 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.qa.webhosting.cals.wisc.edu.
Authors: Sue Lueloff and Brian Hudelson, UW-Plant Pathology
Last Revised: 03/02/2024
D-number: D0115
Tobacco mosaic causing a blotchy light and dark coloring (mosaic) of tobacco leaves.
What is tobacco mosaic?
Tobacco mosaic is a common viral disease of worldwide distribution that affects over 200 species of herbaceous and, to a lesser extent, woody plants. Common hosts include tobacco, solanaceous vegetables (e.g., pepper, tomato) and vining vegetables (e.g., cucumber, melon, squash), as well as a wide range of ornamentals (e.g., begonia, coleus, geranium, impatiens, million bells, petunia). The disease has its biggest impact on vegetables, where it can reduce yield and affect quality to the point that commercial crops cannot be marketed.
What does tobacco mosaic look like?
Symptoms of tobacco mosaic vary in type and severity depending on the plant infected, plant age, the variant of the virus involved, and environmental conditions. On leaves, typical symptoms include blotchy light and dark areas (called mosaic); cupping, curling, elongation (strapping), roughening, wrinkling and other growth distortions; and smaller than normal size. Fruits may have a blotchy color, ripen unevenly, be malformed or have an off flavor. Entire infected plants are often stunted. Other viral diseases like cucumber mosaic (see UW Plant Disease Facts D0036, Cucumber Mosaic) can cause symptoms similar to tobacco mosaic. Often, multiple viral diseases can simultaneously affect a single plant. Certain herbicide exposures (see UW Plant Disease Facts D0060, Herbicide Damage), nutrient deficiencies or toxicities, high temperature and even insect feeding can also cause similar symptoms. Proper diagnosis of tobacco mosaic requires lab testing.
Where does tobacco mosaic come from?
Tobacco mosaic is caused by Tobacco mosaic virus (TMV), the first virus ever identified. Numerous variants (strains) of the virus have subsequently been described. TMV survives in infected plants (including viable seeds), as well as in debris from these plants. Plant-based products (most notoriously tobacco products) can harbor the virus. TMV is very stable and can survive for long periods of time; there are reports of TMV surviving and remaining infectious after 50 years in storage at 40°F. Because of its stability, TMV can survive on and be picked up from hands, clothing, gardening tools, work surfaces and any other object (e.g., door knobs) that gardeners may handle.
TMV is highly transmissible and is commonly spread by handling infected plants, then healthy plants. Spread via gardening tools is also very common. No specific insects spread TMV (the way that aphids spread Cucumber mosaic virus). However, bees and chewing insects (e.g., grasshoppers) can transmit TMV through casual contact or their feeding as they move from plant to plant.
Leaf growth distortions caused by tobacco mosaic.
How do I save a plant with tobacco mosaic?
There is no cure for tobacco mosaic. Once infected, plants remain infected for life, and typically the virus spreads throughout the plant from the point of infection. Infected plants and any associated debris should be burned (where allowed by local ordinance) or double-bagged and disposed of in a landfill. DO NOT compost plants with this disease. Thoroughly decontaminate any items that have come into contact with infected plants or their debris by treating them for a minimum of one minute with:
2.75 tablespoons Alconox® (a lab detergent) plus 2.5 tablespoons sodium lauryl sulfate (SLS), also known as sodium dodecyl sulfate (SDS), in one gallon of water, or
14 dry ounces of trisodium phosphate in one gallon of water.
These ingredients can be ordered on the internet. If you decide to use SLS (SDS), be sure to wear gloves, safety goggles and a dust mask, and mix the solution in a well-ventilated area as SLS (SDS) is a known skin and eye irritant. Once treated, rinse items with sufficient water to remove any residues. Also, thoroughly wash your hands with soap and water, and launder any clothing that you wore while disposing of infected plants and debris.
How do I avoid problems with tobacco mosaic virus in the future?
Inspect plants prior to purchase for any symptoms of tobacco mosaic, and DO NOT buy symptomatic plants. Purchase seed from a reputable supplier that routinely inspects their seed-producing plants for symptoms of viral (and other) diseases. If you use tobacco products, DO NOT use them around plants. Also, wash your hands thoroughly with soap and water prior to handling plants, and consider wearing freshly laundered clothing when gardening. Finally, decontaminate (as described above) any items that might harbor TMV to help prevent spread. Even if you do not use tobacco products, routine handwashing and decontamination of gardening tools and other items can help prevent tobacco mosaic from being a problem.
For more information on tobacco mosaic:
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 Brenda Dahlfors, Tom German, Jenna LaChance and Diane Lorenz 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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-number: D0108
What is sudden oak death?
Sudden oak death (SOD), also called Ramorum leaf blight or Ramorum dieback, is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California. The disease can affect or has been reported in association with a wide range of woody and herbaceous plants including, but not limited to bigleaf maple (Acer macrophyllum), Bodnant viburnum (Viburnum X bodnantense), ‘Brouwer’s Beauty’ pieris (Pieris floribunda X japonica), California bay laurel (Umbellularia californica), California buckeye (Aesculus californica), California coffeeberry (Rhamnus californica), California honeysuckle (Lonicera hispidula), canyon live oak (Quercus chrysolepis), coast redwood (Sequoia sempervirens), doublefile viburnum (Viburnum plicatum var. tomentosum), douglas-fir (Pseudotsuga menziesii var. menziesii), evergreen huckleberry (Vaccinium ovatum), Formosa firethorn (Pyracantha koidsumii), ‘Forest Flame’ pieris (Pieris formosa X japonica), Himalaya pieris (Pieris formosa), Japanese camellia (Camellia japonica), Japanese pieris (Pieris japonica), laurustinus (Viburnum tinus), madrone (Arbutus menziesii), manzanita (Arctostaphylos manzanita), rhododendron (Rhododendron spp.), Sasanqua camellia (Camellia sasanqua), toyon (Heteromeles arbutifolia), western starflower (Trientalis latifolia), and witch hazel (Hamamelis virginiana), Burkwood viburnum (Viburnum X burkwoodii), California hazelnut (Corylus cornuta), Camellia X williamsii, cascara (Rhamnus purshiana), Chinese pieris (Pieris formosa var. forrestii), common lilac (Syringa vulgaris), David viburnum (Viburnum davidii), drooping leucothoe (Leucothoe fontanesiana), European beech (Fagus sylvatica), European cranberrybush viburnum (Viburnum opulus), European turkey oak (Quercus cerris), European yew (Taxus baccata), fragrant viburnum (Viburnum farreri), grand fir (Abies grandis), Holm oak (Quercus ilex), horse-chestnut (Aesculus hippocastanum), lingonberry (Vaccinium vitis-ideae), mountain laurel (Kalmia latifolia), Northern red oak (Quercus rubra), Pieris formosa var. forrestii X Pieris japonica, poison oak (Toxicodendron diversiloba), Prague viburnum (Viburnum X pragense), reticulate camellia (Camellia reticulata), salmonberry (Rubus spectabilis), Southern red oak (Quercus falcata), strawberry tree (Arbutus unedo), sweet chestnut (Castanea sativa), Viburnum X carlcephalum X Viburnum utile, Victorian box (Pittosporum undulatum), wayfaringtree viburnum (Viburnum lantana), and wood rose (Rosa gymnocarpa).
Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.
SOD was first reported in the US in California and has subsequently been found in other US states, including in Wisconsin in 2019. SOD has also been reported in Europe.
What does sudden oak death look like?
Symptoms of SOD vary depending upon the plant species infected. On some hosts, infections occur primarily on leaves leading to light brown leaf spots and blotches. These leaf symptoms may be indistinguishable from other, more common, leaf spots and blights, or may mimic sunburn or leaf scorch symptoms. Twigs and branches that become infected often wilt, forming a “shepherd’s-crook”, and subsequently die back. Infection of tree trunks leads to cankers (i.e., sore-like areas) that produce large amounts of an amber to black colored ooze. This ooze can dry to form a stained area on the bark. Removing the bark over the affected area will reveal discolored wood beneath that sometimes (but not always) has a black border. Cankers can eventually expand to girdle trunks, thus resulting in the death of the tree or shrub. Trunk infections appear not to extend into the root system of the plant. Once SOD cankers develop, other pathogens may invade the infected areas, accelerating tree or shrub death and complicating the diagnosis of the disease.
Where does sudden oak death come from?
SOD is caused by the fungus-like water mold Phytophthora ramorum, which was first recognized as a pathogen in 1995. Phytophthora ramorum can be spread over long distances through movement of infected plants or infested plant parts. The organism can also be moved with contaminated soil (e.g., on vehicle tires, tools, or shoes), or in contaminated water. Once established on plants in a given location, the organism produces reproductive structures (called sporangia) that can be moved from plant to plant by rain splash, or wind. Phytophthora ramorum was introducing into Wisconsin in 2019 on nursery stock grown in the state of Washington.
Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.
How do I save a plant with sudden oak death?
If you believe you have seen a plant that has SOD, please IMMEDIATELY submit a sample to the UW-Madison Plant Disease Diagnostics Clinic (PDDC). See below for address details. Double bag suspect plant tissue in sealable plastic bags and place the bagged specimen in a box or envelope for shipping. Include contact information (complete address, phone number, email address) in a separate sealable plastic bag with the sample. Tape over all of the edges of boxes and envelopes used for shipping to keep everything sealed inside. Write on the box or envelope that the box or envelope contains a suspect SOD sample. If you have questions about collecting or submitting a sample, contact PDDC staff at (608) 262-2863 or at pddc@wisc.edu.
Because Phytophthora ramorum is a regulated, quarantined pathogen, DO NOT remove the affected plant (or parts thereof) or take the plant from the site where it is located, other than to collect a specimen for submission for a diagnosis. Be sure to decontaminate any tools or other items that come into contact with the plant (including those used to collect a diagnostic sample) by treating them for at least 30 seconds in 10% bleach. Thoroughly rinse and oil tools after decontamination to prevent rusting. If a plant tests positive for Phytophthora ramorum, it will be removed and destroyed to help prevent further spread of the pathogen.
How do I avoid problems with sudden oak death in the future?
Carefully inspect any new nursery stock upon delivery (or prior to purchase, if possible) for symptoms of SOD. Keep new stock isolated from older stock as long as possible, to minimize possible movement of the pathogen should the disease develop after plants have arrived. If you see any suspect symptoms, alert the PDDC so that arrangements can be made for proper testing for Phytophthora ramorum.
For more information on sudden oak death:
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 Lis Friemoth, Lisa Johnson, and Ann Joy for reviewing this document and to David Rizzo of the University of California-Davis for the use of his photos.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Janet van Zoeren, UW-Madison Entomology, and Patricia McManus, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-number: D0101
What is silver leaf?
Silver leaf is a fungal disease that affects a wide range of deciduous trees. The disease has its biggest impact in fruit trees such as apple, pear and cherry, but can also affect ornamental trees such as willow, poplar, maple, oak, and elm. Silver leaf has traditionally been considered a disease of older trees that have been physically damaged or are in decline due to other diseases. However, beginning in 2017, severe cases of silver leaf have been observed on young, healthy apple trees in commercial orchards in Wisconsin.
Young, vigorous high-density apple trees, with trees showing symptoms of silver leaf (on the right) adjacent to those that do not (on the left).
What does silver leaf look like?
The first symptom of silver leaf is a silver sheen that appears on leaves of affected trees. The number of leaves affected can vary dramatically from tree to tree. The silver sheen develops when the epidermis of a leaf (i.e., the surface layer of cells) separates from the rest of the leaf, altering the way that the leaf reflects light. The silvery leaves may also have brown, dead patches. Leaf symptoms may appear one year, but may be less severe or even nonexistent in subsequent years.
Note that other tree stresses (particularly environmental stresses) can cause leaf symptoms similar to those of silver leaf. An additional symptom that can help in identifying silver leaf is dark staining just under the bark of branches with symptomatic leaves. This staining can extend several inches down a branch. Eventually, white edged, purple-brown, shelf-like conks (reproductive structures of the fungus that causes the disease) will appear on branches and/or trunks of the diseased trees.
Where does silver leaf come from?
Silver leaf is caused by the fungus Chondrostereum purpureum. Spores of the fungus are released from conks during wet periods in the autumn and spring and infect trees at pruning scars or other open wounds (e.g., wounds from branches breaking during severe storms or due to heavy, wet spring snow). The fungus lives in the xylem (i.e., the water-conducting tissue) of infected branches, and its presence in the xylem leads to the dark staining as described above. A toxin released by the fungus moves up into the leaves causing the epidermis separation that leads to the silver sheen of the leaves. Eventually, wood in infected branches begins to decay, at which point the fungus starts producing conks.
How do I save a tree with silver leaf?
On trees with limited damage, prune out branches showing leaf symptoms. Also watch for any conks, and immediately remove branches where these are present. Removing conks limits production of spores that can lead to infections in other trees. When pruning, cut branches at least four inches below where you can see staining under the bark or where conks are visible. Decontaminate pruning tools after each cut by treating them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants), a commercial disinfectant or 10% bleach. If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting.
The silver sheen of leaves typical of silver leaf (left) and conks (i.e., reproductive structures) of the silver leaf fungus, Chondrostereum purpureum (right).
In plantings where silver leaf symptoms are widespread, pruning out all symptomatic branches may not be practical, and the loss of that many branches might cause more harm than good. Also, trees sometimes show symptoms one year but then appear to recover in subsequent years. Therefore, instead of pruning symptomatic branches, consider marking diseased trees. Carefully watch the marked trees each year to see if symptoms reoccur or if the trees lose vigor. If trees lose vigor and/or conks become visible, then the trees should be removed. Because the silver leaf fungus limits water movement in infected branches, make sure that affected trees receive adequate water. In general trees should receive approximately one inch of water per week during the growing season from natural rain and/or irrigation. Eventually infected trees will likely decline to the point where they should be removed. In some instances, monitoring trees may not be feasible. In such situations, removing trees the first year that they show silver leaf symptoms may be the best management option.
Any branches or trunk sections removed from trees with silver leaf should be disposed of by burning (where allowed by local ordinance) or burying.
How do I avoid problems with silver leaf in the future?
Whenever possible, prune trees during the winter during dry periods when temperatures are below 32°F. If you must prune during the growing season, only prune during dry periods. Pruning at these times will decrease the risk of infection by the silver leaf fungus through pruning wounds. DO NOT use pruning paints or sealants when pruning. At this time, there are no fungicides for silver leaf control.
For more information on silver leaf:
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, Annie Deutsch, and Bryan Jensen 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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0058
What are Gymnosporangium rusts?
Gymnosporangium rusts are a group of closely related diseases caused by fungi that infect both junipers (in particular red cedar) and woody plants in the rose family such as, but not limited to, apple, crabapple, hawthorn and quince. These fungi must infect both types of plants to complete their life cycles. The most common Gymnosporangium rusts found in Wisconsin are cedar-apple rust, cedar-hawthorn rust and cedar-quince rust. The names of these diseases are somewhat misleading, given that all three diseases can affect multiple rosaceous hosts in addition to those referenced in their names.
Yellow cedar-apple rust spots on an apple leaf (left) and slimy, orange, gelatinous cedar-apple rust galls on a juniper branch (right).
What do Gymnosporangium rusts look like?
On junipers, symptoms of Gymnosporagium rusts vary. Cedar-hawthorn and cedar-apple rust fungi induce formation of irregularly-shaped brown galls, with cedar-hawthorn rust galls tending to be smaller in size (approximately 1/8 to 9/16 inch in diameter) than cedar-apple rust galls (approximately 1/4 to 2 inches in diameter). Both types of galls produce distinctive slimy, orange, gelatinous appendages in the spring. In contrast, the cedar-quince rust fungus causes juniper branch swellings. Orange spores ooze from these swollen areas in the spring.
On rosaceous hosts, Gymnosporangium rust symptoms also vary. Symptoms of cedar-hawthorn rust and cedar-apple rust appear in mid to late May, typically as circular, yellow-orange areas on leaves. Eventually, tube-like structures (that have a fringe-like appearance) form on the undersides of leaves beneath the yellow spots. Symptoms of cedar-quince rust typically become obvious later in the summer (most commonly on hawthorns) as swollen, spiny branches and/or fruits.
Where do Gymnosporangium rusts come from?
Several fungi in the genus Gymnosporangium cause Gymnosporangium rusts. These include Gymnosporangium juniperi-virginianae (cedar-apple rust), Gymnosporangium globosum (cedar-hawthorn rust), and Gymnosporangium clavipes (cedar-quince rust). These fungi overwinter in infected branches and galls on junipers. Spores oozed from the infected branches or produced in the gelatinous gall appendages drift to rosaceous hosts leading to leaf and fruit infections. Similarly, spores produced in the tube-like structures/spines on rosaceous leaves and fruits drift to junipers leading to new branch infections and additional gall formation.
How do I save a tree or shrub with Gymnosporangium rust?
Gymnosporangium rusts are primarily cosmetic diseases that make susceptible plants unattractive, but rarely have long-term detrimental effects. Gymnosporangium rusts on leaves can, for all practical purposes, be ignored. Gymnosporangium rusts on juniper branches can be easily managed by pruning approximately four to six inches below swollen areas or galls. Rosaceous hosts with infected branches can be pruned similarly. Be sure to decontaminate pruning tools between cuts by treating them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants) or 10% bleach. Decontaminating tools will prevent movement of rust fungi from branch to branch or from plant to plant during pruning. If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting.
Cedar-quince rust on hawthorn fruit.
How do I avoid problems with Gymnosporangium rusts in the future?
The best way to avoid Gymnosporangium rusts is to not grow junipers (particularly red cedar) and susceptible rosaceous hosts close to one another. In urban settings where yards are small however, keeping both hosts adequately separated may be impossible. Where Gymnosporangium rusts have consistently been a problem, consider using evergreens (e.g., pine, fir, spruce) and flowering trees and shrubs (e.g., cherry, plum, lilac) that are immune to these diseases. If you decide that you want to mix junipers with apple, crabapple, hawthorn, and quince on your property, check at your local nursery for resistant varieties that will satisfy your landscaping needs. In general, Chinese junipers (Juniperus chinensis) tend to be relatively resistant to Gymnosporangium rusts.
Fungicides treatments are also available to control Gymnosporangium rusts, although such treatments should be considered only as a last resort. Among fungicides marketed for use by home gardeners, those containing chlorothalonil, copper, mancozeb, myclobutanil, propiconazole, and sulfur are labeled for use for Gymnosporangium rust control. These products may be useful for controlling Gymnosporangium rusts on rosaceous hosts, but will likely not be effective if used on junipers. For optimal control on rosaceous hosts, apply treatments when flower buds first show color, when half of the flowers are open, at petal-fall, seven to 10 days after petal fall and finally 10 to 14 days later. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the products(s) in the safest and most effective manner possible. In particular, be sure that you select appropriate products when treating trees and shrubs with edible fruit. If you decide to use propiconazole or myclobutanil, alternate use of these active ingredients with use of at least one of the other active ingredients listed above (but DO NOT alternate propiconazole with myclobutanil) to help minimize potential problems with fungicide-resistant strains of Gymnosporangium rust fungi.
For more information on Gymnosporangium rusts:
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 Laura Jull, Darrin Kimbler, Sharon Morrisey, Charlene Schmidt and Janet Van Zoeren 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.qa.webhosting.cals.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.qa.webhosting.cals.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.qa.webhosting.cals.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.qa.webhosting.cals.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.qa.webhosting.cals.wisc.edu.
