The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL on
August 11, 2008

Verticillium Wilt

Gail Ruhl, Sr. Plant Disease Diagnostician, Department of Botany & Plant Pathology

Verticillium wilt, a soil-borne fungal disease, is known for its wide host range including maple, ash, catalpa, redbud, tulip tree, golden rain tree, Russian olive, smoke tree and others. Although Verticillium Wilt can show up at any time during the growing season, symptoms most commonly appear as summer approaches and weather warms.

As a soil-borne disease, the fungus enters the tree through root or root-collar wounds. Once inside the tree, the fungus colonizes the xylem elements within the tree’s vascular system and interferes with water movement. Hot weather increases the tree’s water demands and infected branches wilt and die – sometimes in a matter of days. Usually, only a few branches are affected at a time, though it is possible for the entire tree to go down at once.

Streaking within the vascular tissue or wood often accompanies external dieback symptoms. The streaking may be scattered throughout a branch if the tree has been infected for a long period of time or it may be confined to new sapwood, indicating a new infection. Peeling back the bark of wilting branches may reveal streaked sapwood if the discoloration has spread up into the smaller branches. The actual color of the streaking is dependent upon the host. In maple, the discoloration tends to be greenish, but colors range from gray-green to brown or black. Since discoloration may also be caused by other factors, it is advisable to send suspect branch samples from wilting trees to the Purdue Plant and Pest Diagnostic Lab for accurate diagnosis. Samples should be 6 to 12 inches long and about thumb-size in diameter. Send the sample early in the week so it doesn’t spend the weekend at the post office.

Very little can be done for diseased trees other than pruning out infected branches and trying to keep trees as healthy as possible by watering during dry weather and mulching the soil under the tree if feasible. It is important to disinfect pruning tools between cuts with a 10 percent household bleach solution or rubbing alcohol to discourage further spread of the disease. This disease can remain in the soil for long periods. If you must replant a tree killed by this disease, use resistant species. Trees with good resistance include pine, arborvitae, juniper, ginkgo, mountain ash, birch, crabapple, apple, sweetgum,
hackberry, hawthorn, linden, honeylocust, oak, pawpaw, pear, sycamore, London Planetree, walnut and willow.

See BP-6-W: Verticillium Wilt of Shade Trees

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Verticillium on maple

Maple tree exhibiting symptoms of Verticillium Wilt

Verticillium on  maple

Maple tree exhibiting symptoms of Verticillium Wilt

Verticillium on maple branch

Diagnostic green discoloration of vascular system in maple

Verticillium on redbud

Redbud tree exhibiting symptoms of Verticillium Wilt

Verticillium on redbud branch

Brown discoloration in the vascular system of Redbud infected by
Verticillium

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service