Category Archives: Disease – Broad Leafed Woody Ornamental

Blister Canker

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UW Plant Disease Facts

 

Authors:   Ariana Abbrescia, Brian Hudelson, and Leslie Holland, UW-Madison Plant Pathology
Last Revised:   03/06/2024
D-number:   D0134

What is blister canker?

Blister canker (also known as nailhead canker) is a potentially lethal disease that primarily affects apple and crabapple trees.  Other trees and shrubs grown in Wisconsin that can be affected by the disease include American elm, honey locust, hornbeam, magnolia, mountain-ash (rowan), oak, pear, and serviceberry.

Nondescript trunk blackening on a serviceberry due to blister canker (left). Stromata of the blister canker fungus (right). [Photos courtesy of Jake Kubisiak, Wachtel Tree Science (left) and Serenella Linares, mycologist and board member of the Mycological Association of Washington, D.C. (right)]
Nondescript trunk blackening on a serviceberry due to blister canker (left). Stromata of the blister canker fungus (right). [Photos courtesy of Jake Kubisiak, Wachtel Tree Science (left) and Serenella Linares, mycologist and board member of the Mycological Association of Washington, D.C. (right)]

What does blister canker look like?

Symptoms of blister canker often appear as darkened, sunken areas (i.e., cankers) that extend from cracks or wounds on tree branches and trunks.  These areas can be large, extending up to three feet in length.  Initially, particularly in young trees, affected areas may have a mottled appearance due to a mix of diseased and healthy tissue.  As the disease progresses, affected branches die and the bark peels away.  Trunk infections can lead to tree death. 

Within affected areas on branches and trunks, dark, round, flat structures (called stromata) form.  These structures range from 1/8 to 3/8 inches in diameter.  Stromata resemble nailheads and often form in clusters, giving the bark a blistered appearance.  In the early stages of symptom development, blister canker may be difficult to distinguish from other canker diseases [e.g., fire blight (see UW Plant Disease Facts D0052, Fire Blight), Nectria canker (see UW Plant Disease Facts D0074, Nectria Canker)].  However, the appearance of stromata helps distinguish blister canker from other diseases. 

Where does blister canker come from? 

Blister canker is caused by the fungus Biscogniauxia marginata, which survives on infected apple (or other) trees in both living and dead wood.  Spores of the fungus (produced in the stromata) blow from tree to tree, and the fungus infects through wounds (e.g., pruning sites, broken branches).  The fungus subsequently spreads under the bark. 

How do I save a tree with blister canker? 

Once a tree is infected by the blister canker fungus, it cannot be cured.  Infected branches can be removed by pruning approximately six to eight inches below the canker.  Decontaminate pruning tools after each cut by treating them for at least 30 seconds with bleach diluted to a final concentration of 0.5% sodium hypochlorite (the active ingredient) or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).  If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting.  Trees with trunk infections may survive for several years, but you should remove them immediately to limit spread of the blister canker fungus.  Burn (where allowed) or bury infected branches and trunk sections. 

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

Blister canker often affects trees that are stressed due to drought, poor soil fertility, or (for fruit-bearing trees) excessive fruit production.  Addressing these underlying issues can help prevent blister canker.  Established deciduous trees (like the ones affected by blister canker) require approximately one inch of water per week from the time that they begin to leaf out in the spring, through the summer, and into the fall up until they begin to turn their normal fall color.  If there is insufficient rain, apply supplemental water around the drip lines of trees (i.e., the edges of where the branches extend) using drip or soaker hoses.  To address soil fertility issues, have a soil sample tested for nutrients, and fertilize based on the test results.  The UW Soil and Forage Lab (https://uwlab.soils.wisc.edu/) can assist with this testing.  Thinning fruits to prevent overbearing is another practice that reduces tree stress.  Ideally, fruit thinning should be carried out at the earliest stage possible, typically within three to four weeks after bloom, when the fruits are still small.

Properly prune tree species susceptible to blister canker on a regular basis so that they grow properly and are less prone to storm damage.  Pruning routinely also allows for removal of smaller branches, leaving wounds that are less likely to become infected by the blister canker fungus.  Pruning larger branches from older trees can create large wounds that increase the risk of infection.  For details on proper tree pruning, see University of Wisconsin Garden Facts XHT1014, Pruning Deciduous Trees

For more information on blister canker: 

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


This Fact Sheet is also available in PDF format:

© 2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Lisa Johnson, Vijai Pandian, and Mary Kay Thompson for reviewing this document.

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

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

Plant Problems to Watch for in 2023

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UW Plant Disease Facts

 

Authors:   Brian Hudelson UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0132
 
Lipstick Rust Lipstick Rust
Host:   Chinese juniper, apple, crabapple
Pathogen:   Gymnosporangium yamadae
Signs/Symptoms:   Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
Boxwood Blight Boxwood Blight
Host:   Boxwood
Pathogens:   Calonectria pseudonaviculata
Signs/Symptoms:   Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:   UW Plant Disease Facts D0023
Late Blight Late Blight
Host:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:   Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:   UW Plant Disease Facts D0068
Septoria Leaf Spot and Early Blight Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:   Spotting and eventual total collapse of leaves, working from the bottom of the plant up
For more information see:   UW Plant Disease Facts D0100/46
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:   Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:   Dead spots on leaves, potentially leading to complete leaf browning
Verticillium Wilt Vascular Discoloration Verticillium Wilt
Hosts:   Woody and herbaceous ornamentals, vegetables
Pathogens:   Verticillium sp.
Signs/Symptoms:   Wilting, branch dieback, plant death
For more information see: UW Plant Disease Facts D0121/D0122
Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruit, vegetables, turf
Pathogens:   miscellaneous powdery mildew fungi
Signs/Symptoms:   Powdery white growth on leaves
For more information see:   UW Plant Disease Facts D0084/86/87
Rhizosphaera Needle Cast 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
Diplodia Shoot Blight and Canker Diplodia Shoot Blight and Canker
Hosts:   Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:   Dieback of brand tips with dead needles showing uneven lengths
For more information see:   UW Plant Disease Facts D0042
Chlorosis Chlorosis
Hosts:    Pin oak, red maple, birch, azalea, white pine, blueberry
Pathogen:   None
Signs/Symptoms:   Yellow leaves with dark green veins
For more information see:   UW Plant Disease Facts D0030
Improper Planting Improper Planting
Hosts:   Woody trees and shrubs
Pathogen:   None
Signs/Symptoms:   No root flare at the soil line, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death

For more information on plant problems to watch for:

See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.


This Fact Sheet is also available in PDF format:

© 2022-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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, Lisa Johnson and Carol Shirk for reviewing this document. Thanks also to David Clement (boxwood blight), Nancy Gregory-University of Maryland (lipstick rust), Amanda Gevens (late blight), and Marissa Wilmot (Septoria leaf spot of lilac) for use of their photos.

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

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

Plant Problems to Watch for in 2022

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UW Plant Disease Facts

 

Authors:   Brian Hudelson UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0132
 
Boxwood Blight Boxwood Blight
Host:   Boxwood
Pathogens:   Calonectria pseudonaviculata
Signs/Symptoms:   Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:   UW Plant Disease Facts D0023
Lipstick Rust Lipstick Rust
Host:   Chinese juniper, apple, crabapple
Pathogen:   Gymnosporangium yamadae
Signs/Symptoms:   Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
Late Blight Late Blight
Host:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:   Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:   UW Plant Disease Facts D0068
Septoria Leaf Spot and Early Blight Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:   Spotting and eventual total collapse of leaves, working from the bottom of the plant up
For more information see:   UW Plant Disease Facts D0100/46
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:   Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:   Dead spots on leaves, potentially leading to complete leaf browning
Wood Rots Wood Rots
Hosts:   Woody trees and shrubs
Pathogens:   Miscellaneous wood rot fungi
Signs/Symptoms:   Shelf-like growths on trunks and branches
Canker Diseases Canker Diseases
Hosts:    Woody trees and shrubs
Pathogens:   Miscellaneous canker fungi
Signs/Symptoms:   Sunken areas on trunks/branches
For more information see:   UW Plant Disease Facts D0027, D0037, D0042, D0055, D0074, D0114
Virus Diseases Virus Diseases
Hosts:   All plants, particularly herbaceous ornamentals
Pathogen:   Miscellaneous plant viruses
Signs/Symptoms:   Blotchy leaf color, growth distortions
For more information see:   UW Plant Disease Facts D0036, D0063, D0067, D0115, D0116, D0130
Rhizosphaera Needle Cast 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
Chlorosis Chlorosis
Hosts:    Pin oak, red maple, birch, azalea, white pine, blueberry
Pathogen:   None
Signs/Symptoms:   Yellow leaves with dark green veins
For more information see:   UW Plant Disease Facts D0084
Improper Planting Improper Planting
Hosts:   Woody trees and shrubs
Pathogen:   None
Signs/Symptoms:   No root flare at the soil line, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death

For more information on plant problems to watch for:

See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.


This Fact Sheet is also available in PDF format:

© 2022-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Julie Hill, Jeannie Manis and Carol Shirk for reviewing this document. Thanks also to David Clement (boxwood blight), Nancy Gregory-University of Maryland (lipstick rust), Amanda Gevens (late blight), Marissa Wilmot (Septoria leaf spot of lilac), and Diane Malchow (wood rots) for use of their photos.

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

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

Boxwood Blight – Pest Alert

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UW Plant Disease Facts

 

Pest Alert
Authors:   Matthew Shulman* and Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   02/28/2024
D-number:   D0023

What is boxwood blight? 

Boxwood blight (also known as box blight and boxwood leaf drop) is a devastating disease of boxwood (Buxus spp.) that can cause leaf loss and eventual death of affected shrubs.  Boxwood shrubs are commonly grown as hedges and as individual plants in home landscapes and public gardens.  Boxwood blight can affect any type of boxwood (Buxus spp.) including European or common boxwood (Buxus sempervirens), Korean littleleaf boxwood (B. sinica var. insularis), and Japanese littleleaf boxwood (B. microphylla var. japonica).  In addition, the disease has been reported on Japanese and Allegheny pachysandra (Pachysandra terminalis and Pachysandra procumbens respectively), two common groundcovers.  Boxwood blight has been found in Europe and New Zealand, and was first confirmed in the U.S. in 2011.  The disease was first detected in Wisconsin (in Kenosha County) in 2018.  It has subsequently been found in Dane, Door, Milwaukee, Ozaukee, Portage, and Walworth Counties. 

Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)
Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)

What does boxwood blight look like? 

Initially, brown spots appear on the leaves.  The spots eventually enlarge and merge together.  Infected leaves turn brown and fall off.  Boxwood blight can cause total leaf loss on a shrub within days of the first onset of symptoms.  Dark brown to black sunken areas can also form anywhere on the stems, leading to branch dieback  Boxwood blight often kills plants shortly after all of the leaves drop.  Damage from winter burn (see UW Plant Disease Facts D0127, Winter Burn), dog urine and other diseases such as Volutella blight may look superficially similar to symptoms of boxwood blight. 

Where does boxwood blight come from? 

Boxwood blight is caused by the fungus Calonectria pseudonaviculata (sometimes referred to as Cylindrocladium pseudonaviculatum or Cylindrocladium buxicola) which thrives in humid, warm conditions.  The fungus is typically introduced into any area on nursery plants that are infected, but not showing symptoms.  Holiday wreaths containing boxwood sprigs have also been documented as a source of the boxwood blight fungus.  Once the fungus has been introduced into the landscape, spores can be easily spread by splashing water (e.g., rain or sprinklers), wind or contaminated gardening tools (e.g., pruners, shovels, gloves).  The boxwood blight fungus can survive and produce spores in dead boxwood leaves and branches (including those that have fallen onto the ground) for several years.

How can I save a plant with boxwood blight? 

Because boxwood blight is new to Wisconsin and relatively rare, eradicating the causal fungus may be possible.  Therefore, if you find boxwood blight, remove and destroy any affected shrubs.  Currently, free testing for boxwood blight is available through the UW-Madison Plant Disease Diagnostics Clinic (https://pddc.wisc.edu/).  Plants (roots and all) confirmed to have boxwood blight, as well as any leaves or branches that have fallen from these plants, should be removed and destroyed by burning (where allowed by local ordinance), deep burying (at least two feet deep) or double bagging (in plastic garbage bags), then landfilling.  DO NOT compost any parts of infected shrubs.  Thoroughly decontaminate any tools used in the removal process by treating them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants) or (as a last resort) in 10% bleach.  If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

How can I avoid problems with boxwood blight in the future?  

Consider using shrubs other than boxwood in your landscape.  If you decide to use boxwood, choose boxwood blight resistant varieties where possible.  Common boxwood variety ‘Katerberg’ (North Star®); littleleaf boxwood varieties ‘Compacta’, ‘John Baldwin’, ‘Little Missy’, and ‘Northern Emerald’; Japanese littleleaf boxwood varieties ‘Eseles’ (Wedding Ring®), ‘Green Beauty’, ‘Gregem’ (Baby Gem™), ‘Jim Stauffer’, ‘Peergold’ (Golden Dream™), ‘SB108’ (NewGen Independence®), ‘SB300’ (NewGen Freedom®), and ‘Winter Gem’; Korean littleleaf boxwood varieties  ‘Franklin’s Gem’, ‘Nana’, ‘Pincushion’, ‘Wee Willie’, ‘Winter Beauty’, and ‘Wintergreen’; and hybrid boxwood varieties ‘Green Gem’ and ‘Karzgreen (Green Ice®) have been documented to be resistant to boxwood blight and are rated as hardy in at least one of the USDA hardiness zones (4, 5 or 6) found in Wisconsin.  Always buy boxwood shrubs from local, reputable suppliers who have thoroughly inspected boxwood plants for evidence of boxwood blight.  

Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)
Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)

Isolate new boxwood shrubs from established boxwoods for several weeks before planting, as boxwood blight symptoms not become apparent until weeks after purchase.  DO NOT plant boxwoods in areas where boxwood blight has been a problem in the past, as the fungus can survive in boxwood debris (e.g., leaves and branches) for several years.  When planting, space boxwood plants far enough apart from each other, as well as other shrubs, so that branches on adjacent shrubs do not overlap.  This will increase air flow between plants and promote a drier environment that will be less favorable for boxwood blight development.  Avoid watering plants with sprinklers or overhead with hoses; instead use a soaker or drip hose.  This will limit splash of spores from plant to plant and also promote a drier environment that is less favorable for disease. 

Be cautious when buying holiday wreaths or other garlands.  Avoid holiday decorations that contain boxwood, whenever possible.  If you are unsure whether a wreath that you have purchased contains boxwood, assume that it does, and dispose of it appropriately by burning, deep burying or double bagging and landfilling as described above.  Be careful to collect and dispose of any leaves or branches that may have fallen from wreaths as well.  Make sure that no potentially contaminated materials end up near boxwood shrubs in your yard.  Under NO circumstances should you attempt to compost any suspected boxwood materials. 

Once boxwood blight has been reported near your location, you may want to consider using preventative fungicide treatments for management.  Fungicides containing chlorothalonil (alone or in combination with thiophanate-methyl or tebuconazole), fludioxonil, metconazole, and tebuconazole (as a stand-alone product) have been shown to provide good control of boxwood blight if applied prior to the development of any symptoms.  These fungicides will not cure existing disease.  If you decide to use fungicides, you will need to treat every seven to 14 days throughout the growing season.  DO NOT use fludioxonil, metconazole, or tebuconazole 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 (except DO NOT alternate metconazole and tebuconazole as these products are chemically related).  Alternating active ingredients will help minimize problems with fungicide-resistant strains of the boxwood blight fungus.  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. 

Finally, routinely (e.g., weekly) check boxwood plants for boxwood blight.  Immediately remove any symptomatic plants and fallen leaves and branches, and dispose of them as described above. 

For more information on boxwood blight: 

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


This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 590 at the University of Wisconsin Madison.

© 2019-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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, Carolyn Levine, Randy Levine, Carol Shirk, and Ann Wied for reviewing this document.

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

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

Thyronectria Canker

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW Plant Pathology
Last Revised:   03/02/2024
D-number:   D0114

What is Thyronectria canker? 

Thyronectria canker is a common fungal disease of honeylocust (Gleditsia triacanthos), occurring wherever this tree is grown.  Black locust (Robinia pseudoacacia) and Kentucky coffeetree (Gymnocladus dioicus) have also been reported to be susceptible to the disease.  Thyronectria canker is non-lethal and typically causes relatively minor damage to affected trees.

Thyronectria canker leads to sunken areas on honeylocust branches that are peppered with black spots.
Thyronectria canker leads to sunken areas on honeylocust branches that are peppered with black spots.

What does Thyronectria canker look like?  

Thyronectria canker causes branch dieback.  Affected branches are typically relatively small in diameter (approximately one inch or less), although larger branches can become infected.  On smaller branches, distinct sunken areas (cankers) form at the point of infection.  Within the sunken area, small dark-brown to black spots are typically visible.

Where does Thyronectria come from?  

Thyronectria canker is caused by the fungus Thyronectria austoamericana (sometimes written Thyronectria austo-americana).  The spots visible within the sunken areas on infected branches are clusters of fruiting bodies (i.e., reproductive structures) of the fungus.  These structures produce multicelled, light- to medium-brown spores that, when released, can blow to susceptible trees, leading to new infections.  Long periods of wet weather are favorable for infection to occur.

How do I save a tree with Thryronectria canker? 

Remove infected branches by pruning four to six inches below obviously infected areas on branches.  Be sure to prune only when it is dry, and be sure to disinfest pruning tools between cuts by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), spray disinfectants (as long as they contain 60 to 70% alcohol) or 10% bleach.  If you use bleach, be sure to thoroughly rinse and oil tools after you are done pruning to prevent rusting.  Dispose of branches by burning (where allowed) or burying them.  DO NOT use fungicides for control of this disease.

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

Make sure your honeylocust tree is properly fertilized and watered to reduce stress and promote vigorous growth.  Fertilize your honeylocust only if you have soil and foliage nutrient tests that indicate nutrient deficiencies that need to be corrected.  The UW Soil and Forage Lab (https://uwlab.soils.wisc.edu/) can assist with testing.  An established honeylocust tree (i.e., a tree that has been planted for three or more years) requires approximately one inch of water per week from the time it buds out in the spring, through the summer and into the fall up until it starts to turn its normal fall color.  When there is insufficient rain, water at the drip line of the tree (i.e., the edge of where the branches extend), or more extensively in the root zone if possible, using a drip or soaker hose.  Remove grass out to the drip line of the tree, and mulch this area with a high quality mulch (e.g., shredded oak bark mulch, one of the cedar mulches).  Use one to two inches of mulch if you have a heavier (e.g., clay) soil and three to four inches if you have a lighter (e.g., sandy) soil.  Keep mulch four inches from the trunk of the tree.  Finally, consider routine maintenance pruning by a certified arborist (see https://www.waa-isa.org/) to thin the canopy of your honeylocust tree.  Thinning will provide better airflow through the tree, promoting more rapid drying of branches and leaves, thus leading to a less favorable environment for infections to occur.

For more information on Thyronectria canker: 

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


This Fact Sheet is also available in PDF format:

© 2021-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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, Bann Gabelt and Laura Jull for reviewing this document.

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

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

Lichens

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UW Plant Disease Facts

 

Authors:   Ken Frost* and Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0072
 
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

What are lichens?

Lichens are organisms that arise from mutually beneficial interactions between certain filamentous fungi, algae and yeasts.  The filamentous fungi provide the physical structures of the lichens, as well as protection for the algae and yeasts.  The algae produce food for the fungi and yeasts via photosynthesis.  The yeasts are thought to produce compounds to fend off disease-causing organisms and insect pests.

What do lichens look like?

Lichens come in four basic growth forms. Crustose lichens are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens are leaf-like and composed of flat sheets of tissue that are not tightly bound together. Squamulose lichens are composed of scale-like parts. Fruticose lichens are composed of free-standing branching tubes.

Where do lichens come from?

Lichens are everywhere. There are an estimated 13,500 to 17,000 species of lichens, and lichens can be found growing in tropical, temperate and polar regions throughout the world. Lichens will grow on almost any surface that is stable and reasonably well-lit. In temperate regions, lichens can often be found growing on the bark of trees or old fence posts. Others lichens grow in less hospitable places, such as bare rock surfaces or old headstones in graveyards, where they aid in the breakdown of rocks and the formation of soil.

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

How do I save a tree with lichens?

DO NOT PANIC! Lichens do not harm trees; they are not pathogens or parasites, and do not cause disease. Lichens are self-reliant, with the algal component of the lichen producing food for the organism via photosynthesis. Lichens absorb water and minerals from rainwater and the atmosphere, and because of this, they are extremely sensitive to air pollution. As a result, the presence or absence of certain lichen species can be used as an indicator of levels of atmospheric pollutants. Information on the abundance and species of lichens growing in an area can give a good indication of the local air quality.

For more information on lichens:

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


This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison.

© 2005-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Lisa Johnson, Barb Larson and Mike Maddox for reviewing this document. Thanks also to the Wisconsin State Herbarium and Marie Trest for providing 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.

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

Plant Diseases to Watch For in 2021

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0081
 
Septoria Leaf Spot Septoria Leaf Spot and Early Blight
Host:  Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:  Spotting and eventual total collapse of leaves working from the bottom of the plant up
For more information see:       UW Plant Disease Facts D0100/46
Late Blight Late Blight
Hosts:  Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:  Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:       UW Plant Disease Facts D0068
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:  Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:  Dead spots on leaves, potentially leading to complete leaf browning
Rhizosphaera Needle Cast 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
Gymnosporangium Rusts 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
Elderberry Rust Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Apple Scab Scab (Apple and Pear)
Hosts:   Apple, crabapple, pear, mountain-ash
Pathogens:   Venturia inaequalis, Venturia pirina
Signs/Symptoms:  Feathery-edged spots on leaves and fruits often leading to leaf loss and tree defoliation
For more information see:       UW Plant Disease Facts D0004
Bur Oak Blight Bur Oak Blight
Host:   Bur oak
Pathogen:   Tubakia iowensis
Signs/Symptoms:  Wedge-shaped dead areas on leaves leading to dead leaves that stay attached to trees
Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Diplodia Shoot Blight and Canker 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
Boxwood Blight Boxwood Blight
Host:  Boxwood
Pathogen:   Calonectria pseudonaviculata
Signs/Symptoms:  Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:       UW Plant Disease Facts D0023

For more information on plant diseases to watch for: 

See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.


This Fact Sheet is also available in PDF format:

© 2021-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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, Margaret Murphy and Denise Worzalla-Rocha for reviewing this document. Thanks also to Amanda Gevens (late blight), Marissa Wilmot (Septoria leaf spot of lilac), Jenell Bindl (elderberry rust), Lina Rodriguez-Salamanca (bur oak blight) and David Clement (boxwood blight) for use of their photos.

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

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

Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/02/2024
D-number:   D0112
 
Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Tar Spot Tar Spot
Hosts:  Maples
Pathogen:   Rhytisma spp.
Signs/Symptoms:  Tarry areas (either solid spots or clusters of small spots) on leaves
For more information see:       UW Plant Disease Facts D0110
Peach Leaf Curl Peach Leaf Curl
Hosts:  Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
For more information see:       UW Plant Disease Facts D0076
Sooty Mold Sooty Mold
Hosts:  Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
For more information see:       UW Bulletin A2637
Chlorosis 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
Gymnosporangium Rusts 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
Black Knot Black Knot
Hosts:  Prunus spp. (plum and cherry)
Pathogen:   Apiosporina morbosa
Signs/Symptoms:  Black poop-like growths on branches
For more information see:       UW Plant Disease Facts D0018
Elderberry Rust Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Golden Canker Golden Canker
Hosts:  Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
For more information see:       UW Plant Disease Facts D0055
Dog Vomit Slime Mold Dog Vomit Slime Mold
Hosts:  Any plant and on mulch
Cause:   Fuligo septica
Signs/Symptoms:  Scrambled egg-like masses on mulch or at the base of plants
For more information see:       UW Plant Disease Facts D0102

For more information on common plant 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.


This Fact Sheet is also available in PDF format:

© 2021-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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, Mike Maddox and Ann Wied for reviewing this document.

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

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

Deciduous Tree Leaf Disease Quick Reference

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UW Plant Disease Facts
 
Authors:  Brian Hudelson, UW-Madison Plant Pathology
Last Revised:  02/29/2024
D-number:  D0041
 
Anthracnose 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 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 Leaf Spot 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 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 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 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 Downy Leaf Spot
Hosts:  Hickory, walnut
Pathogen:  Microstroma juglandis
Signs/Symptoms:  Discrete powdery white areas on lower leaf surfaces
 Clorosis 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 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 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.


This Fact Sheet is also available in PDF format:

© 2009-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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.

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

Elderberry Rust

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UW Plant Disease Facts

 

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)
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.


This Fact Sheet is also available in PDF format:

© 2021-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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.wisc.edu.

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