Verticillium Wilt in Maples
The Verticillium wilt fungus blocks water-conducting tissue and thus impedes water movement in the tree. This results in wilting. If the tree is healthy, it may be able to withstand an initial attack, but continued invasion by the fungus will result in the death of the tree.
How can you tell if a maple tree is infected with the Verticillium fungus? Although symptoms can vary due to the season of the year and environmental factors, most often in the early stages, leaves on diseased branches appear off-color and are limp. You might see these symptoms on an individual branch in the tree crown or throughout the entire tree. The disease can progress slowly, over several months or growing seasons, but these trees are usually stunted, lacking in vigor and eventually may die. Sometimes the affected foliage turns dry and brittle and drops from the tree in a matter of days or weeks. This type of wilting can result in rapid branch and tree mortality.
Symptoms can develop at any time throughout the growing season, but they are more common in late spring and early summer in this area. Verticillium wilt can be diagnosed from the streaking in the sapwood of diseased branches. In maples, the discoloration is dark green to black. But since other diseases or mechanical damage can cause wood discoloration, only a diagnostic laboratory can confirm or deny the presence of Verticillium wilt. Contact your County Extension Office for guidelines on how to take a sample.
The Verticillium fungus can survive long periods in the soil or in infected plant tissue, and usually enters a tree through root or root collar wounds caused by insects or mechanical injuries. Cool temperatures favor infection, which is why most disease symptoms are seen in late spring. The fungus is less active in hot weather.
The best way to avoid Verticillium wilt is prevention and sanitation. First, mulch around your trees, keeping the mulch about 1-2 inches away from the trunk, so the possibility of mechanical injury from weed whackers and lawn mowers is greatly reduced. Second, susceptible trees should not be planted in areas where the disease has previously occurred. When choosing new plant material, remember that, in addition to maple, the following species are susceptible to verticillium wilt: Catalpa, Russian olive, redbud, smoketree, goldenrain tree, cherry and barberry. But many trees and shrubs are resistant to the fungus and can be planted in infested soil, they include: pines, spruce, yew, junipers, arborvitae, apple and crabapple, hackberry, sweetgum, sycamore, walnut, hickory, and linden.