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Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 04/15/2021
X-number: XHT1283
Powdery Mildew Powdery Mildew
Hosts:    Herbaceous and woody ornamentals, fruits, vegetables
Pathogens:    Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:        UW Garden Facts XHT1005a/b/c
Tar Spot - Ten Common Plant Diseases 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 Garden Facts XHT1126
Peach Leaf Curl Peach Leaf Curl
Hosts:   Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
For more information see:        UW Garden Facts XHT1069
Sooty Mold Sooty Mold
Hosts:   Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
For more information see:        UW Bulletin A2637
Chlorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:        UW Garden Facts XHT1002
Gymnosporangium Rusts Gymnosporangium Rusts
Hosts:   Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:        UW Garden Facts XHT1009
Black Knot Black Knot
Hosts:   Prunus spp. (plum and cherry)
Pathogen:   Apiosporina morbosa
Signs/Symptoms:  Black poop-like growths on branches
For more information see:        UW Garden Facts XHT1056
Elderberry Rust Elderberry Rust
Hosts:   Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:        UW Garden Facts XHT1280
Golden Canker Golden Canker
Hosts:   Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
For more information see:        UW Garden Facts XHT1125
Dog Vomit Slime Mold Dog Vomit Slime Mold
Hosts:   Any plant and on mulch
Cause:   Fuligo septica
Signs/Symptoms:  Scrambled egg-like masses on mulch or at the base of plants
For more information see:        UW Garden Facts XHT1091

For more information on common plant diseases: Contact your county Extension agent.


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