Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 04/18/2025
D-number: D0136
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
Septoria Leaf Spot of Lilac Host: Lilac Pathogen: Septoria sp. Signs/Symptoms: Dead spots on leaves, potentially leading to complete leaf browning
Aster Yellows Hosts: Many herbaceous ornamentals and vegetables Pathogens: Aster yellows phytoplasma Signs/Symptoms: Yellow/orange/purple leaves, stunted and distorted growth, leafy flowers, brooming For more information see: UW Garden Facts D0007
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 D0058/0131
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
Bacterial Canker Hosts: Stone fruits (cherry, peach, plum) Pathogen: Pseudomonas syringae Signs/Symptoms: Masses of sap on affected branches/trunks, branch die back, tree death For more information see:UW Plant Disease Facts D0009
Powdery Mildew Hosts: Herbaceous and deciduous 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
Septoria Leaf Spot and Early Blight Host: Tomato Pathogens: Septoria lycopersici and Alternaria solani Signs/Symptoms: Spotting and eventual total death of leaves working from the bottom of the plant up For more information see: UW Plant Disease Facts D0100/46
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 (Abiotic) Signs/Symptoms: Yellow leaves with dark green veins For more information see: UW Plant Disease Facts D0030
For more information on plant problems to watch for in 2025: 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).
Thanks to Julie Hill, Kathy Johnson and Margaret Murphy for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 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.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.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.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:
See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
Thanks to Diana Alfuth, 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.
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:
See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
Thanks to 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.
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:
See https://pddc.wisc.edu/ or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
Thanks to Diana Alfuth, 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.
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
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.
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.
Authors: Patricia McManus and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0076
What is peach leaf curl?
Peach leaf curl is a common disease of peach and nectarine trees throughout the Midwest and eastern U.S. Where the disease is severe, tree vigor and fruit quality and yield are reduced. Peach leaf curl often becomes more prevalent after relatively mild winters, which are more favorable for the survival of the organism that causes the disease. A related disease, plum pockets, affects plums.
Leaf distortions and discoloration typical of peach leaf curl.
What does peach leaf curl look like?
Diseased leaves are distorted with puckered, thickened, twisted areas that can be light green, yellow, or reddish to purple in color. Leaves later turn brown and fall from the tree. Diseased shoots are stunted with small, yellowish leaves, or have leaves arranged in tight whorls (rosettes). Diseased flowers may abort, leading to reduced fruit set, while diseased fruit are bumpy, reddish in color, and fall prematurely.
Where does peach leaf curl come from?
Peach leaf curl is caused by the fungus Taphrina deformans, which overwinters in bark and bud scales of peach and nectarine trees. Fungal spores infect leaves and shoots in the spring while leaves are still in the bud and as they just begin to emerge. Mild (50 to 70°F), wet weather during this period favors infection. Additional spores form on the surface of diseased tissue, and these spores cause new infections if the weather remains mild and wet.
How do I save trees that have peach leaf curl?
Peach leaf curl is unlikely to kill a peach or nectarine tree on its own. However, if significant premature leaf drop occurs, trees will be susceptible to drought stress and winter injury. To help maintain tree vigor, apply water (approximately one inch per week) at the drip lines (i.e., the edges of where the branches extend) of peach and nectarine trees during dry periods. Also, fertilize trees with nitrogen, but avoid fertilizing after August 1; late season fertilization will prevent trees from hardening off properly before winter, making them prone to winter injury. Finally, thin fruit if the crop load is heavy.
How do I avoid problems with peach leaf curl in the future?
Because Taphrina deformans survives in bark and bud scales, removing diseased leaves in the fall will not reduce disease. To prevent serious problems with peach leaf curl, plant resistant or tolerant peach varieties (e.g., ‘Frost’, ‘Indian Free’, ‘Q-1-8’, varieties derived from ‘Redhaven’). Avoid growing susceptible varieties (e.g., those derived from ‘Redskin’). In addition, consider applying a single fungicide spray in the fall after leaf drop or in the spring before buds begin to swell to control peach leaf curl (and also plum pockets). Effective fungicide active ingredients include chlorothalonil, copper (e.g., Bordeaux mixture), and ferbam. Choose a fungicide that is labeled for use on edible fruit crops, and read and follow all label instructions to ensure that you use the product in the safest and most effective manner possible.
For more information on peach leaf curl:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.
Thanks to Patti Nagai, Teryl Roper, and Ann Wied for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.
Authors: Brian Hudelson UW-Madison Plant Pathology
Last Revised: 02/29/2024
D-number: D0049
What is elderberry rust?
Elderberry rust is a visually striking fungal disease that affects stems, leaves and flowers of plants in the genus Sambucus (i.e., elderberries). The disease also affects sedges (Carex spp.). On elderberries grown as ornamentals, as well as on sedges, the disease is primarily a cosmetic problem. However, if elderberries are grown for fruit, the disease can disrupt flower and fruit formation, thus reducing fruit yield.
An elderberry rust gall on elderberry (left) and leaf spots caused by elderberry rust on sedge (right). Photos courtesy of Jenell Bindl (left) and Michele Warmund, University of Missouri (right)
What does elderberry rust look like?
Elderberry rust is most noticeable on elderberries where it causes growth distortions and swellings (i.e., galls) on leaves and stems. Galls are often very large, bright yellow and powdery from spores produced by the causal fungus. In extreme cases, galls can resemble banana slugs that have attached themselves to branches. Infected flowers become thick, swollen and green-tinged rather than white. Affected plant parts are covered with a network of small (approximately 1/16 inch in diameter) ring-like spots. These spots are reproductive structures of the rust fungus and produce the powdery spores that coat the galls.
On sedges, elderberry rust causes brownish leaf spots, often with yellow halos. The spots eventually erupt releasing powdery, rusty-orange spores.
Where does elderberry rust come from?
Elderberry rust is caused by the fungus Puccinia sambuci, also known as Puccinia bolleyana. The fungus overwinters in sedge debris, and spores produced in this debris blow to elderberry plants in the spring, leading to infection and gall formation. Spores produced in elderberry galls blow back to sedges, where infection of newly produced leaves (and other plant parts) occurs. These infections lead to spotting and to the formation of a third type of spore that reinfects sedges causing additional spotting. Late in the season a fourth type of spore is produced that serves as the overwintering phase of the fungus. Infection of both elderberries and sedges is favored by wet weather.
How do I save plants with elderberry rust?
Elderberry rust is not a lethal disease on either elderberry or sedge. When galls form on elderberry, simply prune these out. This will make elderberry plants more aesthetically pleasing and limit spread of the fungus to sedges. When pruning, cut branches four to six inches below each gall. Between cuts, decontaminate pruning tools by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), a spray disinfectant containing 60-70% active ingredient, or a 10% bleach solution (i.e., one part of a disinfecting bleach and nine parts water). If you decide to use bleach, be sure to rinse your tools thoroughly after you are done pruning and then oil them to prevent rusting, which can be caused by bleach use. Dispose of galls by burning (where allowed by local ordinance) or burying them.
How do I avoid problems with elderberry rust in the future?
In landscape settings, the best way to avoid problems with elderberry rust is to remove any sedges that are growing near elderberry plants. The farther the distance between elderberries and sedges, the less likely that elderberry rust will be an issue. Also, increase airflow around elderberry plants by thinning them and removing surrounding plants. Increased airflow will dry plants more rapidly and make the environment less favorable for infection. DO NOT use a sprinkler to water plants, as that wets leaves and provides a better environment for infections to occur. Instead, use a soaker or drip hose to apply supplemental water to the soil at the drip lines of the plants (i.e., the edges of where the branches extend). While fungicides are available for rust control in commercial elderberry production, these products are not recommended for use in home garden settings.
For more information on elderberry rust:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.
Thanks to Katherine Amann, Kaitlyn Davis, and Ann Wied for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.