Septoria Leaf Spot and Early Blight
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 the UW-Madison Plant Disease Diagnostics Clinic website (https://pddc.wisc.edu/) or contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at 608-262-2863 or pddc@wisc.edu.
© 2021-2026 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.
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)
Submit additional lawn, landscape, and gardening questions at the Ask a Gardening Question page (https://hort.extension.wisc.edu/ask-a-gardening-question/) of the University of Wisconsin-Madison Division of Extension Horticulture website.