I have recently received a rash of phone calls and office visits from people with maple leaves that are browning and wilting. Every sample that has come through the door is infected with anthracnose.
Anthracnose diseases are caused by various naturally occurring fungi that are capable of infecting stems, branches, leaves and fruits of a wide variety of deciduous trees and shrubs. Sycamore, ash, maple, oak and privet are especially susceptible.
These diseases can be found throughout the eastern United States. The symptoms of these diseases are more severe in years of extended cool, wet spring weather. And there is no doubt that our spring has been cool and wet. There is no other way to explain our recent weather.
But just because you have one of these trees, it does not mean that your tree will be infected with anthracnose. Symptoms vary according to the plant part and the host attacked. Leaf infections may show irregular dead blotches or brown lesions associated with large leaf veins. Infections on new shoots may kill them entirely or cause severe tissue distortion.
Defoliation may occur early in the season followed by a second growth of leaves in early summer. Buds are often invaded and killed. Twig lesions often expand and may girdle the twig entirely, causing death of the parts beyond the lesion. Repeated twig dieback may alter the form of the tree, causing crooked branches and "witches'-brooms" (a development of clusters of twigs around a common point on a branch).
Cankers form on the branches as a result of the death of buds and twigs and may remain active beyond one dormant season, girdling and killing branches. Cankers may also be inactivated by callus formation near the margins. Large trees that sustain repeated attacks by the pathogen are severely weakened showing loss of vigor, dieback of large branches and increased susceptibility to insect borers and winter injury.
RESISTANCE VARIETIES
Anthracnose over-winters in leaf debris and infected twigs and branches. In spring, it produces spores that are carried by air currents to young buds of the host. Spores germinate under moist conditions and infect leaf tissue. If moist conditions continue, the first generation of new spores is produced in the infected leaf tissue and the cycle continues.
Fortunately, good control of some anthracnose diseases can be obtained by destroying infected plant material and debris in which these fungi over-winter. Gathering and destroying leaves or composting them under several inches of soil and pruning out infected twigs reduces the amount of available spores and reduces the severity of the disease.
When planting trees and shrubs that are normally susceptible to anthracnose diseases, preference should be given to resistant varieties. London Plane (Platanus X. acerifolia) may be planted in place of susceptible sycamore. Control of many anthracnose diseases can be accomplished through properly timed sprays of fungicides. If needed, landscape trees in New York state may be treated registered pesticides. Although there are several fungicides registered in the state for anthracnose, most are not available to the home owner. Consider speaking with your local extension educator regarding your situation and whether or not a professional should be hired to spray your landscape trees. A good pruning and fall leaf clean-up is all the average homeowner may need to do to help control anthracnose.
Anne Lenox Barlow is the horticulture educator with Cornell Cooperative Extension in Clinton County. Office phone numbers: Clinton County 561-7450, Essex County 962-4810, Franklin County 483-7403. E-mail questions to: askMG@cornell.edu.
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Tree disease affecting leaves
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