Pruning Deciduous Trees

Laura Jull, UW-Madison Horticulture, UW-Extension Revised:  8/13/2012 Item number:  XHT1014 Why prune trees? Pruning is important for a variety of reasons.  Pruning can help control the size of a tree, direct growth, influence flowering or fruiting, or maintain plant health and appearance.  Pruning can also increase the safety of a tree by removing broken, diseased, […]

Black Walnut Toxicity

Ann Joy and Brian Hudelson, UW-Madison Plant Pathology Revised:  5/7/2010 Item number:  XHT1017 What is black walnut toxicity? Black walnut trees (Juglans nigra) produce a toxic substance (called juglone) that prevents many plants from growing under or near them. Related trees like butternut (J. cinerea) and shagbark hickory (Carya ovata) also produce juglone, but in […]

Ash Flower Gall

Phil Pellitteri, UW Insect Diagnostic Lab, UW-Extension Revised:  8/6/2012 Item number:  XHT1048 What is wrong with my ash tree?  Galls are abnormal plant growth that can be caused by insects, mites or plant diseases.  On ash trees, a tiny eriophyid mite causes male flowers to grow into round greenish, 1∕2 to 1 inch diameter tumor-like […]

Bacterial Blight

Gina Foreman* and Brian Hudelson, UW-Madison Plant Pathology *Completed as partial fulfillment of the requirements for Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison. Revised:  4/25/2004 Item number:  XHT1093 What is bacterial blight?  Bacterial blight, also known as blossom blight or shoot blight, is a common and often […]

Ash Yellows

Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology *Completed as partial fulfillment of the requirements for a BS in Plant Pathology at the University of Wisconsin Madison. Revised:  8/6/2012 Item number:  XHT1079 What is ash yellows?  Ash yellows is a chronic, systemic disease that affects ash trees of all ages.  White ash is particularly susceptible […]

Armillaria Root Disease

Michael Amman, UW-Madison Forest Ecology and Management and Glen R. Stanosz, Ph. D., UW-Madison Plant Pathology Revised:  8/6/2012 Item number:  XHT1120 What is Armillaria root disease?  Armillaria root disease, also known as shoestring root rot, is an often lethal disease of tree and shrub roots and lower stems.  It can affect almost any conifer or […]


Brian Hudelson, UW-Madison Plant Pathology Revised:  3/10/2012 Item number:  XHT1001 What is anthracnose?  Anthracnose is the name of several common fungal diseases that affect the foliage of woody ornamentals in Wisconsin.  Trees that are most commonly and severely affected by anthracnose include ash, maple, white oak, sycamore, and walnut.  Anthracnose typically affects young leaf tissue. […]

Black Knot

Brian Hudelson, UW-Madison Plant Pathology, UW-Extension Revised:  5/1/2010 Item number:  XHT1056 What is black knot?  Black knot is a disfiguring and potentially lethal disease of trees and shrubs in the genus Prunus.  This genus includes stone fruits such as wild, fruit-bearing and ornamental plums and cherries. What does black knot look like?  During the first […]


Ken Frost* and Brian Hudelson, UW-Madison Plant Pathology Revised:  4/28/2012 Item number:  XHT1027 What are lichens?  Lichens are organisms that arise from mutually beneficial interactions between certain fungi and algae.  The fungi provide the physical structures of the lichens, as well as protection for the algae.  The algae, in turn, produce food for the fungi […]

Sudden Oak Death

Authors: Brian Hudelson, UW-Madison Plant Pathology Last Revised: 08/23/2019 X-number: XHT1024 What is sudden oak death?  Sudden oak death (also called Ramorum leaf blight or Ramorum dieback) is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California. […]

Eastern Redbud, Cercis canadensis

Need a small tree with spring flowers and interesting structure? Unless you live way up north eastern redbud may fit the bill. With selected strains and cultivars hardy to zone 4, this North American native offers showy pink flowers in early spring before most other trees are even leafing out. To learn more about Cercis canadensis, read this article…

Homeowner Guide to Emerald Ash Borer Insecticide Treatments

Pest Alert Authors: PJ Liesch and R. Chris Williamson, UW Entomology Last Revised: 04/07/2022 X-number: XHT1181 Emerald ash borer insecticide treatment considerations.  Several insecticide products are available to homeowners for control of emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may […]

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