Question: All the leaves have fallen off the branches in one section of my maple tree. Do you know what is going on? M.A.
Answer: Trees drop leaves for a number of reasons but leaf loss in a limited defined area points to verticillium wilt. Verticillium wilt affects a wide range of deciduous trees and shrubs. I’ve seen it most often on maple, ash, smoke-tree and redbud.
Verticillium wilt is caused by fungi which are commonly found in Wisconsin soils and in roots, branches and leaves of infected plants. Trees and shrubs struggling from weather extremes (e.g. 2014 winter cold, 2012 drought), poor growing conditions, or other stresses are most susceptible to verticillium.
The first signs of verticillium wilt are individual branches that suddenly wilt and die. Affected branches may occur on one side of the tree or may be scattered throughout the tree. If you carefully peel away the bark of these branches, you may see brown or green streaking in the sapwood just under the bark. Streaking is common in trees such as maple or redbud, but often is not visible in ash trees.
Your tree can be tested for verticillium wilt by submitting branch samples from the infected section to the University of Wisconsin Plant Disease Diagnostic Clinic. Standard testing fee is $20. For more information go to http://pddc.wisc.edu or contact my office.
There is no cure for verticillium wilt and most often the tree dies. However, you can extend the life of your tree by watering, mulching, and fertilizing properly. Prune out dead branches as they occur. Clean your pruning tools between cuts by dipping them a minimum of 30 seconds in a 10-percent bleach solution or alcohol (spray disinfectants that contain at least 70-percent alcohol can also be used). This will prevent spreading verticillium from branch to branch or from tree to tree.
Don’t use wood chip mulches from infected trees. Collect and discard leaves that have fallen from symptomatic trees. Mulch and leaves are potential sources of verticillium.
If, or when, your maple dies, replace it with a verticillium resistant tree. Resistant deciduous trees and shrubs include apple, azalea, beech, birch, butternut, crabapple, dogwood, flowering quince, ginkgo, hackberry, hawthorn, hickory, holly, honeylocust, katsuratree, oak, pear, poplar, sweetgum, sycamore, walnut, and willow. Pines, spruces and firs are also resistant.
Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at email@example.com or call her at 262-857-1942.