Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

This article is provided by the UW Plant Disease Diagnostics Clinic.

Powdery Mildew

Hosts: Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens: Miscellaneous powdery mildew fungi
Signs/Symptoms: Powdery white growth on leaves
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Tar Spot

Hosts:   Maples
Pathogen:   Rhytisma spp.
Signs/Symptoms:  Tarry areas (either solid spots or clusters of small spots) on leaves
More information on tar spot

Peach Leaf Curl

Hosts:   Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
More information on peach leaf curl

Sooty Mold

Hosts:   Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
More information on sooty mold

Chlorosis

Hosts: Oak, red maple
Cause: Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms: Yellow leaves with dark green veins
More information on chlorosis

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)
More information on Gymnosporangium rusts

Black Knot

Hosts: Prunus spp. (plum and cherry)
Pathogen: Apiosporina morbosa
Signs/Symptoms: Black poop-like growths on branches
More information on black knot

Elderberry Rust

Hosts:   Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
More information on elderberry rust

Golden Canker

Hosts:   Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
More information on golden canker

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
More information on slime molds

UW Plant Disease Facts

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/02/2024
D-number:   D0112

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.

Send a Plant Sample for Analysis

Be cautious when self-diagnosing plant health issues. Very few diseases can accurately be diagnosed by eye.

Contact the UW Plant Disease Diagnostics Clinic (PDDC), and for a small fee, clinic staff can examine a plant, determine the cause of the disease/disorder, and provide advice on how to control or prevent the issue.

Submit a Sample

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