Category Archives: Disease – Fruit Crop

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Quick Reference Guide

Plant Problems to Watch for in 2024

April 30, 2024 ddlang

UW Plant Disease Facts

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:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Needled Woody Ornamental

Red Star Rust

April 28, 2024 ddlang

UW Plant Disease Facts

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.

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.

This Fact Sheet is also available in PDF format:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop

Blister Canker

March 8, 2024 ddlang

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)]

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:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Quick Reference Guide

Plant Problems to Watch for in 2023

November 13, 2022 ddlang

UW Plant Disease Facts

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.qa.webhosting.cals.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:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Quick Reference Guide

Plant Problems to Watch for in 2022

April 28, 2022 ddlang

UW Plant Disease Facts

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.qa.webhosting.cals.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:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Quick Reference Guide

Plant Diseases to Watch For in 2021

May 11, 2021 ddlang

UW Plant Disease Facts

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.qa.webhosting.cals.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:

Full Color PDF

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.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc, Quick Reference Guide

Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

April 30, 2021 ddlang

UW Plant Disease Facts

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.qa.webhosting.cals.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:

Full Color PDF

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.

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

Disease - Fruit Crop

Peach Leaf Curl

April 6, 2021 hudelson

UW Plant Disease Facts

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.

This Fact Sheet is also available in PDF format:

Full Color PDF

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.qa.webhosting.cals.wisc.edu.

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

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental

Elderberry Rust

March 6, 2021 ddlang

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)

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:

Full Color PDF

Thanks to Katherine Amann, Kaitlyn Davis, and Ann Wied for reviewing this document.

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

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

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Specialty Crop, Disease - Vegetable

Tobacco Mosaic

February 19, 2021 ddlang

UW Plant Disease Facts

Authors: Sue Lueloff and Brian Hudelson, UW-Plant Pathology

Last Revised: 03/02/2024

D-number: D0115

Tobacco mosaic causing a blotchy light and dark coloring (mosaic) of tobacco leaves.

What is tobacco mosaic?

Tobacco mosaic is a common viral disease of worldwide distribution that affects over 200 species of herbaceous and, to a lesser extent, woody plants. Common hosts include tobacco, solanaceous vegetables (e.g., pepper, tomato) and vining vegetables (e.g., cucumber, melon, squash), as well as a wide range of ornamentals (e.g., begonia, coleus, geranium, impatiens, million bells, petunia). The disease has its biggest impact on vegetables, where it can reduce yield and affect quality to the point that commercial crops cannot be marketed.

What does tobacco mosaic look like?

Symptoms of tobacco mosaic vary in type and severity depending on the plant infected, plant age, the variant of the virus involved, and environmental conditions. On leaves, typical symptoms include blotchy light and dark areas (called mosaic); cupping, curling, elongation (strapping), roughening, wrinkling and other growth distortions; and smaller than normal size. Fruits may have a blotchy color, ripen unevenly, be malformed or have an off flavor. Entire infected plants are often stunted. Other viral diseases like cucumber mosaic (see UW Plant Disease Facts D0036, Cucumber Mosaic) can cause symptoms similar to tobacco mosaic. Often, multiple viral diseases can simultaneously affect a single plant. Certain herbicide exposures (see UW Plant Disease Facts D0060, Herbicide Damage), nutrient deficiencies or toxicities, high temperature and even insect feeding can also cause similar symptoms. Proper diagnosis of tobacco mosaic requires lab testing.

Where does tobacco mosaic come from?

Tobacco mosaic is caused by Tobacco mosaic virus (TMV), the first virus ever identified. Numerous variants (strains) of the virus have subsequently been described. TMV survives in infected plants (including viable seeds), as well as in debris from these plants. Plant-based products (most notoriously tobacco products) can harbor the virus. TMV is very stable and can survive for long periods of time; there are reports of TMV surviving and remaining infectious after 50 years in storage at 40°F. Because of its stability, TMV can survive on and be picked up from hands, clothing, gardening tools, work surfaces and any other object (e.g., door knobs) that gardeners may handle.

TMV is highly transmissible and is commonly spread by handling infected plants, then healthy plants. Spread via gardening tools is also very common. No specific insects spread TMV (the way that aphids spread Cucumber mosaic virus). However, bees and chewing insects (e.g., grasshoppers) can transmit TMV through casual contact or their feeding as they move from plant to plant.

Leaf growth distortions caused by tobacco mosaic.

How do I save a plant with tobacco mosaic?

There is no cure for tobacco mosaic. Once infected, plants remain infected for life, and typically the virus spreads throughout the plant from the point of infection. Infected plants and any associated debris should be burned (where allowed by local ordinance) or double-bagged and disposed of in a landfill. DO NOT compost plants with this disease. Thoroughly decontaminate any items that have come into contact with infected plants or their debris by treating them for a minimum of one minute with:

2.75 tablespoons Alconox^® (a lab detergent) plus 2.5 tablespoons sodium lauryl sulfate (SLS), also known as sodium dodecyl sulfate (SDS), in one gallon of water, or
14 dry ounces of trisodium phosphate in one gallon of water.

These ingredients can be ordered on the internet. If you decide to use SLS (SDS), be sure to wear gloves, safety goggles and a dust mask, and mix the solution in a well-ventilated area as SLS (SDS) is a known skin and eye irritant. Once treated, rinse items with sufficient water to remove any residues. Also, thoroughly wash your hands with soap and water, and launder any clothing that you wore while disposing of infected plants and debris.

How do I avoid problems with tobacco mosaic virus in the future?

Inspect plants prior to purchase for any symptoms of tobacco mosaic, and DO NOT buy symptomatic plants. Purchase seed from a reputable supplier that routinely inspects their seed-producing plants for symptoms of viral (and other) diseases. If you use tobacco products, DO NOT use them around plants. Also, wash your hands thoroughly with soap and water prior to handling plants, and consider wearing freshly laundered clothing when gardening. Finally, decontaminate (as described above) any items that might harbor TMV to help prevent spread. Even if you do not use tobacco products, routine handwashing and decontamination of gardening tools and other items can help prevent tobacco mosaic from being a problem.

For more information on tobacco mosaic:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Brenda Dahlfors, Tom German, Jenna LaChance and Diane Lorenz for reviewing this document.

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

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