Root and Crown Rots
Pathogens: Assorted root rot fungi/water molds
Signs/Symptoms: Poor growth, branch dieback, discolored and deteriorated roots
For more information see: UW Plant Disease Facts D0094
Planting-Related Issues/Decline
Hosts: Woody trees and shrubs
Pathogens: None (abiotic)
Signs/Symptoms: No visible root flare, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death
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
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
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
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
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
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
Tobacco Rattle
Hosts: Many herbaceous ornamentals and vegetables
Pathogens: Tobacco rattle virus
Signs/Symptoms: Blotchy leaf color; yellow lines, ring spots, or dead spots on leaves; distorted leaf growth
For more information see: UW Plant Disease Facts D0116
For more information on plant problems to watch for in 2026:
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.
© 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 Julie Hill, Denise Rocha and Janell Wehr for reviewing this document.
Thanks also to Marissa Wilmot (Septoria leaf spot of lilac), and Anette Phibbs (tobacco rattle) 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.