Verticillium dahlia Kleb.
Leaves wilted or browned on one or several branches, often remaining attached (flagging); the rest of the tree appears healthy (A). Young trees are often killed by infection. Older trees, except for sweet cherry, can recover from infection, often leafing out in the following year, only to be affected again. Affected trees often have dark streaks in their sapwood of 2–3-year or older wood (B, C). Symptoms become more severe with water stress in midsummer.
Common to all fruit-growing regions in eastern North America.
Any disease or disorder affecting the root system or rootstock/scion union can produce similar above-ground symptoms, but the presence of streaking in the sapwood can be used to distinguish Verticillium wilt from similar disorders.
Sweet cherry is most susceptible, followed by apricot, peach, and nectarine; plums are least affected. Because the fungus is a natural resident of many soils, management is generally through the practice of avoidance; that is, plantings are established in soils where low or undetectable levels of the pathogen occur. Preplanting sites with various grasses or monocots for one or more years before orchard establishment helps to reduce the pathogen in soils where the pathogen was introduced.
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