When you growa smoke tree (Cotinuscoggygria) in your backyard, the leaf color is ornamental throughout thegrowing season. The small tree’s oval leaves are deep purple, gold or green insummer, but light up in yellows, oranges and reds in autumn. If you see yoursmoke tree wilting, it may be a serious fungal disease called verticilliumwilt. This can kill a smoke tree, so it’s best to take precautionsearly. Read on for how to avoid verticillium wilt in smoke trees.
Smoke Tree Wilting
Smoke trees offer gorgeous foliage from the early buds ofspring through the fabulous fall display. But the plant gets its common namefrom the pale pink, frothy flower clusters. The fluffy buff-pink clusters arelight 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 toinspect it right away to make sure you don’t have smoke trees with verticilliumwilt.
Smoke tree verticillium wilt is not specific to theseplants. It is caused by a fungus (Verticilliumdahlia) that attacks trees and also a number of annual and perennial plantspecies. The fungus that causes verticillium wilt in smoke trees can live inthe soil.
Once it gets into the tissues of plants, it producesmicrosclerotia that penetrate the plant roots and enter the plant’s xylemsystem, reducing the amount of water that can get to the leaves. As plant partsdie and decompose, microsclerotia move back into the soil. They can survive therefor 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 thisfungal disease? Look for signs and symptoms of smoke tree verticillium wilt.
Early signs of verticillium wilt in smoke trees includefoliage that lightens, appears scorched or wilts. This discoloration may affectonly one side of the leaf, or it can be limited to the area around the leafmargins. Branches on one side of the tree may seem to wilt suddenly.
As the disease progresses, you may see cankers, elongateddead areas of bark, on the trunks or branches of smoke trees with verticilliumwilt. It is possible that infected smoke trees will die within a few months butcertainly the growth will appear stunted.
Preventing Smoke Tree Verticillium Wilt
There is no effective treatment for smoke tree verticilliumwilt, but there are many cultural practices you can use to prevent this fungaldisease from attacking and killing your smoke tree.
First, you want to make sure that the young trees and otherplants you invite into your garden do not bring this disease with them. Ifverticillium wilt is a problem in your area, you’ll want to testthe soil for microscleritia before you plant anything.
A technique called soilsolarization is sometimes useful in reducing populations of thispathogen. Experts suggest you placeclear plastic paper over smooth, cultivated soil, burying the edges. This trapsthe 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 thosecertified as pathogen-free nursery stock. If you find infected or dead plants,you should replace them with non-susceptible plants and sterilize pruningequipment after each use.
Several shade tree species are susceptible to Verticillium Wilt. Maples are quite susceptible. Ash, catalpa, golden rain tree, smoke tree, magnolia, and redbud, and others can also be affected. Susceptible shrubs include barberry, boxwood, dogwood, lilac, spirea, weigela, and viburnum. Verticillium is not extremely aggressive but can be a problem on stressed trees and shrubs. Samples that have tested positive for the disease in the Plant Disease Clinic this year include green ash, maple, and catalpa.
If the American smoke tree's leaves wilt and begin to turn yellow around the edges, verticillium wilt may be to blame. This soilborne fungal disease can also cause dark streaks in the sapwood. Verticillium wilt blocks the moisture-conducting tissues and may eventually kill the tree. Prune away infected areas and clear fallen leaves and other plant debris from around the tree. Dispose of the material away from the garden. Keep trees healthy to slow the progress of the disease and consider removing severely infected trees.
Symptoms of Verticillium Wilt
The symptoms vary depending on the type of plant.
In trees, symptoms can appear any time but often start in hot, dry weather. The margins of the leaves may brown, looking like they are scorched. The leaves are smaller than usual. Leaves may wilt on some large branches in the crown, or on the entire side of the tree. Eventually those branches die. The tree produces many more seeds than usual.
If you scratch the bark of a branch with wilted leaves, you’ll notice a streaky discoloration of the wood below. Its color varies, ranging from green to black in maples, and brown to black in black locust and other trees. The symptoms are not always consistent. One tree with the disease may show symptoms one year and then seem fine until symptoms restart years later, whereas another tree dies not long after the symptoms appeared.
In potatoes and other vegetables of the nightshade family, the first symptom is usually yellowing of the lower leaves and subsequent wilting. The leaves develop areas of dead brown tissue surrounded by larger areas of yellowing. These symptoms may only appear on one side of the plant. The brown discoloration inside a stem—cut one off and slice it lengthwise to inspect it—also gives you clues.
In strawberries, the outer, older leaves wilt, dry and develop reddish-yellow or dark brown areas at the leaf margins and between veins. The development of new foliage is scarce and new leaves are stunted, possibly also curled up. You might also notice brown streaks on the petioles, on the runners, and in the crown, which will decay in heavily infected plants. New root growth might be stunted, with the growing tips turning black.
Verticillium Wilt - A Serious Disease of Trees and Shrubs
This maple leaf is exhibiting signs of Verticillium wilt.
By Christine Engelbrecht
Extension Plant Pathologist
Iowa State University
The green, leafy branches of a maple or ash tree can provide much-needed refuge from the sun during the hot days of summer. Verticillium wilt, a common but often overlooked disease, can destroy that beautiful shade by causing these trees to wilt and die, sometimes within a few weeks or months.
Verticillium wilt is a fungal disease that affects over 300 species of plants, including many common trees and shrubs. In Iowa, it is most commonly seen on maple, ash, and catalpa trees, although it is also frequently found on smoke tree, viburnum, lilac, cherry, plum and several other trees and shrubs.
Verticillium wilt is caused by a fungus that lives in the tiny tubes (xylem) that carry water through the tree. The fungus essentially blocks these tubes, preventing water flow and causing the plant to wilt. The fungus also produces toxins that poison the plant.
The disease can occur either acutely or chronically. In acute infections, a branch or a section of several branches of the tree may wilt and turn brown rather suddenly. Often other branches soon follow, until most or all of the branches are wilted. Leaves may also turn yellow between the veins, or may drop prematurely. Branches may die back. Acute infections occur when the fungus is living in the newest wood (the sapwood).
In chronic infections, leaves may be smaller than usual or yellow, often with brown edges. The tree may grow poorly and may produce abnormally large seed crops. The tree does not wilt or die quickly, but declines slowly over time. Chronic infections occur when the fungus is living in older wood.
The Verticillium fungus lives in the soil and infects plants through the roots, often entering through wounds, such as wounds that naturally occur as the roots grow through the soil. The fungus survives in the soil as a thread-like body called a mycelium and as microscopic, dark, resistant structures called microsclerotia. These microsclerotia can survive in soil or dead plant material for up to ten years. For this reason, it is virtually impossible to eradicate the fungus from the soil.
The Verticillium fungus is abundant in many soils, and we do not know why it can lay dormant for many years before suddenly attacking a tree that has been growing in a spot for a long time. It is possible that stresses to the tree, such as a drought or living in poor soil, can make it more susceptible to infection.
There are no treatments available to remove the fungus from the soil where it survives. Management relies on keeping trees in good vigor. Trees with recent wilt symptoms may be able to section off (compartmentalize) the infection themselves and recover.
There is no need to quickly remove infected trees, as the fungus lives in the soil and does not spread through the wind. Dead branches should be pruned out to prevent infection by other fungi and to improve the appearance of trees with chronic infections.
Since the fungus lives in the soil, trees that have died from Verticillium wilt should be replaced with resistant species. Luckily, many species of trees and shrubs are unaffected by Verticillium wilt. These include all conifers, crabapple, beech, ginkgo, hackberry, hawthorn, hickory, white oak and poplar, among others. When a tree dies from Verticillium wilt, replacing it with one of these resistant species can help to ensure a steady source of summer shade.