Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 04/27/2024
D-number: D0135
Winter Injury/Winter Burn Hosts: All conifers, particularly yew and juniper Cause: Insufficient water Signs/Symptoms: Needle browning/bleaching over winter or in spring as plants come out of dormancy For more information see: UW Plant Disease Facts D0127
Chlorosis Hosts: Pin oak, red maple, birch, azalea, white pine, blueberry Pathogen: None (Abiotic) Signs/Symptoms: Yellow leaves with dark green veins For more information see: UW Plant Disease Facts D0030
Blister Canker Hosts: Apple, crabapple, serviceberry, mountain-ash Pathogen: Biscogniauxia marginata Signs/Symptoms: Dark, sunken, cracked areas on trunks with dark, round, flat pads of fungal growth For more information see: UW Plant Disease Facts D0134
Golden Canker Hosts: Pagoda dogwood Pathogen:Cryptodiaporthe corni Signs/Symptoms: Dead branches that are gold in color, often with orange spots For more information see: UW Plant Disease Facts D0055
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
Fire Blight Hosts: Apple, crabapple, pear, mountain-ash Pathogen: Erwinia amylovora Signs/Symptoms: Branch dieback (often with the tip having a shepherd’s crook), eventual tree death For more information see: UW Plant Disease Facts D0052
Cucumber Mosaic Hosts: Herbaceous ornamentals and vegetables Pathogens: Cucumber mosaic virus Signs/Symptoms: Blotchy light and dark green leaf color, distorted leaf growth For more information see: UW Plant Disease Facts D0036
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
Red Star Rust Red Star Rust Hosts: Chinese juniper, apple, crabapple Pathogen:Gymnosporangium yamadae Signs/Symptoms: Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple) For more information see: UW Plant Disease Facts D0131
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
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 in 2024: 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:
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 Julie Hill, Margaret Murphy and Denise Rocha for reviewing this document.
Thanks also to Serenella Linares (blister canker), Nancy Gregory-University of Maryland (lipstick rust), 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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 04/26/2024
D-number: D0131
What is red star rust?
Red star rust (also known as Japanese apple rust or lipstick rust) is a type of Gymnosporangium rust (see UW Plant Disease Facts D0012, Gymnosporangium Rusts). The disease affects junipers [specifically Chinese junipers (Juniperus chinensis), flaky juniper (Juniperus squamata), Hollywood juniper (Juniperus chinensis var. kaizuka), Japanese garden juniper (Juniperus procumbens), Sargent juniper (Juniperus chinensis var. sargentii), and savin juniper (Juniperus sabina)], as well as apple and crabapple trees (Malus spp.). The disease is native to Asia (in particular China, Korea and Japan) and was first detected in the US in Delaware and Pennsylvania in 2008. Red star rust was observed in Wisconsin in 2021 and to date has been found in Dane, Kenosha, Milwaukee, Outagamie, Ozaukee, Portage, Racine, and Walworth Counties. Red star rust is of concern because of its potential negative impact in commercial apple production.
A slimy, orange, gelatinous red star rust gall on a juniper branch (left). Red/maroon/fuchsia-colored red star rust spots on crabapple leaves (right). (Photo courtesy of Nancy Gregory, University of Delaware)
What does red star rust look like?
On junipers, red star rust leads to branch swellings or small-diameter galls that sprout 1/8 to 3/8 inch long, flattened, orange, gelatinous protrusions in late spring to early summer. The galls/swellings and gelatinous masses can be confused with those produced by cedar-hawthorn and cedar-quince rust (see UW Plant Disease Facts D0012, Gymnosporangium Rusts for details).
On apples and crabapples, red star rust typically leads to bright red, maroon, or fuchsia-colored leaf spots that become readily visible by mid-summer. Yellow or orange spots surrounded by a red, maroon, or fuchsia margin have also been reported for the disease. Beneath the colorful leaf spots, numerous spiny or tendril-like structures form. Red star rust leaf spots are similar to cedar-apple and cedar-hawthorn rust leaf spots except for their color; cedar-apple rust and cedar-hawthorn rust leaf spots tend to be solid yellow or orange.
In Asia, red start rust can cause severe defoliation of apple trees. Infections on apple fruits are rare.
If you see what you believe is red star rust, please contact the UW-Madison Plant Disease Diagnostics Clinic at (608) 262-2863 or pddc@wisc.edu to make arrangements to submit a sample for a free diagnosis. Samples will be used to determine how widespread the disease is in the state.
Where does red star rust come from?
Red star rust is caused by the fungus Gymnosporangium yamadae. The fungus overwinters in infected branches and galls on junipers.
Spores produced in the gelatinous masses on infected branches and galls spread on air currents to apple and crabapple trees leading to leaf infections. Similarly, spores produced in the tube-like spines on apple and crabapple leaves drift to junipers leading to new branch infections and additional gall formation.
How do I save a tree or shrub with red star rust?
On junipers, prune infected branches to remove the disease. Cut four to six inches below visible galls or areas on a branch that appear to be infected. 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. You can burn (where allowed) or bury pruned branches, or drop them off at your local yard waste disposal site.
Once infections occur on apple and crabapple leaves, there is no cure. Fortunately, cases of red star rust on apple and crabapple trees observed thus far in Wisconsin have not been severe. Damage to apple and crabapple trees has been primarily cosmetic, making trees less attractive but not causing significant leaf loss or yield loss (in fruit-bearing apple trees). No long-term detrimental effects due to the disease have been observed in Wisconsin at this time. All of this said, the negative impacts of red star rust may change as the disease becomes more established and widespread in the state, and during years with wetter weather.
How do I avoid problems with red star rust in the future?
The best way to avoid red star rust is to not grow junipers and apples or crabapples close to one another. In urban settings where yards are small however, keeping both hosts adequately separated may be impossible. Also, Chinese junipers have become increasingly common in many landscape settings because of their resistance to other Gymnosporangium rusts (i.e., cedar-apple rust, cedar-hawthorn rust, cedar-quince rust). If red star rust becomes a serious problem in your area, consider growing evergreens (e.g., pine, fir, spruce) and flowering trees and shrubs (e.g., cherry, plum, lilac) that are immune to the disease.
In Asia, commonly grown apple varieties differ in terms of their susceptibility to red star rust. Apple varieties grown in Wisconsin likely also differ in susceptibility. However, which apple varieties commonly grown in Wisconsin may be resistant (and to what extent) is not known. Also, while fungicides treatments are available to control cedar-apple rust, cedar-hawthorn rust, and cedar-quince rust (see UW Plant Disease Facts D0012, Gymnosporangium Rusts for details), how effective these treatments might be in controlling red star rust is also not known.
For more information on red star 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 Fieweger, Leslie Holland, and Janell Wehr 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: 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)]
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.
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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0132
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 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 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 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 Host: Lilac Pathogen: Septoria sp. Signs/Symptoms: Dead spots on leaves, potentially leading to complete leaf browning
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
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 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 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 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 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:
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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0132
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 Host: Chinese juniper, apple, crabapple Pathogen: Gymnosporangium yamadae Signs/Symptoms: Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
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 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 Host: Lilac Pathogen: Septoria sp. Signs/Symptoms: Dead spots on leaves, potentially leading to complete leaf browning
Wood Rots Hosts: Woody trees and shrubs Pathogens: Miscellaneous wood rot fungi Signs/Symptoms: Shelf-like growths on trunks and branches
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 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 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 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 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:
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.qa.webhosting.cals.wisc.edu.
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)
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.qa.webhosting.cals.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)
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 willnot 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.
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.qa.webhosting.cals.wisc.edu.
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.
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.
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.qa.webhosting.cals.wisc.edu.
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.
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.
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.
*Completed as partial fulfillment of the requirements for Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0081
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 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 Host: Lilac Pathogen: Septoria sp. Signs/Symptoms: Dead spots on leaves, potentially leading to complete leaf browning
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 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 Hosts: Elderberry Pathogen: Puccinia sambuci Signs/Symptoms: Light yellow, powdery growths on branches For more information see: UW Plant Disease Facts D0049
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 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 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 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 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:
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.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-number: D0112
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 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 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 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 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 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 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 Hosts: Elderberry Pathogen: Puccinia sambuci Signs/Symptoms: Light yellow, powdery growths on branches For more information see: UW Plant Disease Facts D0049
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 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
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.qa.webhosting.cals.wisc.edu.
![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)]](https://pddc.qa.webhosting.cals.wisc.edu/wp-content/uploads/sites/39/2024/03/Blister-Canker.png)
