When you grow a smoke tree (Cotinus coggygria) in your backyard, the leaf color is ornamental throughout the growing season. The small tree’s oval leaves are deep purple, gold, or green in summer but light up in yellows, oranges, and reds in autumn. If you see your smoke tree wilting, it may be a serious fungal disease called verticillium wilt. This can kill a smoke tree, so it’s best to take precautions early. Read on for how to avoid verticillium wilt in smoke trees.
Smoke Tree Wilting
Smoke trees offer gorgeous foliage from the early buds of spring through the fabulous fall display. The plant gets its common name from the pale pink, frothy flower clusters. The fluffy buff-pink clusters are light and hazy, looking a little like smoke. The tree lights up the backyard and is both drought resistant and easy care once established.
A smoke tree wilting is not a good sign. You’ll need to inspect it right away to make sure you don’t have smoke trees with verticillium wilt.
Smoke tree verticillium wilt is not specific to these plants. It is caused by a fungus (Verticillium dahlia) that attacks trees and also a number of annual and perennial plant species. The fungus that causes verticillium wilt in smoke trees can live in the soil.
Once it gets into the tissues of plants, it produces microsclerotia that penetrate the plant roots and enter the plant’s xylem system, reducing the amount of water that can get to the leaves. As plant parts die and decompose, microsclerotia move back into the soil. They can survive there for years, waiting to attack another vulnerable plant.
Signs of Verticillium Wilt in Smoke Trees
How to tell if a smoke tree wilting in your garden has this fungal disease? Look for signs and symptoms of smoke tree verticillium wilt.
Early signs of verticillium wilt in smoke trees include foliage that lightens, appears scorched, or wilts. This discoloration may affect only one side of the leaf, or it can be limited to the area around the leaf margins. Branches on one side of the tree may seem to wilt suddenly.
As the disease progresses you may see cankers, elongated dead areas of bark on the trunks or branches of smoke trees with verticillium wilt. It is possible that infected smoke trees will die within a few months but certainly the growth will appear stunted.
Preventing Smoke Tree Verticillium Wilt
There is no effective treatment for smoke tree verticillium wilt, but there are many cultural practices you can use to prevent this fungal disease from attacking and killing your smoke tree.
First, you want to make sure that the young trees and other plants you invite into your garden do not bring this disease with them. If verticillium wilt is a problem in your area, you’ll want to test the soil for microscleritia before you plant anything.
A technique called soil solarization is sometimes useful in reducing populations of this pathogen. Experts suggest you place clear plastic paper over smooth, cultivated soil, burying the edges. This traps the heat. Leave it in place for at least four weeks during the hot summer.
You’ll also want to limit the specimens you plant to those certified as pathogen-free nursery stock. If you find infected or dead plants, you should replace them with non-susceptible plants and sterilize pruning equipment after each use.
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Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.
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