Verticillium wilt is a widespread and serious disease that affects the vascular system of trees. It is caused by two species of fungi that live in the soil: Verticillium albo-atrum and Vertcillium dahlia. The disease affects many types of trees, shrubs, and plants with maple trees being particularly susceptible. That is why it is sometimes called “maple wilt,” though infection is certainly not exclusive to this species.
The fungi that cause verticillium wilt can survive for long periods not only in the soil but also in the roots of both susceptible and non-susceptible plants. The fungi typically enter through wounds in roots or branches and then block the transportation of water and nutrients. Wilting symptoms quickly follow.
Wind and water can carry the fungi to new areas of infection and it may also be carried to a site through infected soil, for example on the soles of shoes. Pruning tools can be another source of contamination so it is important to sanitize them before using them again. The disease can be fatal. Since the pathogen remains in the soil, plants that have succumb should be removed and replaced with resistant species.
As its name implies, the leaves of infected plants wilt and curl before turning color and beginning to brown. Symptoms will spread through the crown and the leaves will eventually fall off. The tree will experience less overall growth and may leaf out late in spring or lose leaves too early in autumn. It is not uncommon for the symptoms to be restricted to one area of the infected plant. Affected areas may not grow any leaves at all. Internally in symptomatic branches and in the roots, streaking discoloration, which varies in color from greenish to brown to nearly black, will be noticeable if you peel back the bark. As wilting symptoms are a common sign of many tree issues, this internal discoloration is an important hallmark for identifying verticillium wilt.
Infected branches should be pruned back to beyond the point where internal sapwood shows characteristic streaking. Tools should be disinfected with a diluted liquid bleach or alcohol solution before pruning healthy branches or nearby healthy trees. Susceptible species should not be planted in soil where it is known that verticillium wilt is present. When a plant begins to seriously decline from the disease, it will likely require removal so it is important to manage overall health. Watering when the weather is dry and fertilizing based on soil analysis are good preventative measures to take.
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