Each species of anthracnose fungus attacks only a limited number of tree species. The fungus that causes sycamore anthracnose, for example, infects only sycamore and not other tree species. Other anthracnose-causing fungi have similar life cycles, but require slightly different moisture and temperature conditions for infection.

Flowering dogwoods, for example, have been particularly hard-hit by another strain in recent years. Horticulturists are working to develop resistant dogwood variants?EUR??,,????'?????<

According to U. of Massachusetts plant pathologist Dan Gillman, there is controversy about the origin of anthracnose. Some researchers think it is an invasive, exotic pathogen introduced on nursery stock, perhaps from Asia. Others think it could be a weak pathogen that mutated and became more virulent as environmental conditions favored and enhanced it.

Anthracnose fungi may cause defoliation of most maple, oak, elm, walnut, birch, sycamore, and hickory species and, occasionally, of ash and linden trees. Damage of this type usually occurs after unusually cool, wet weather during bud break. Single attacks are seldom harmful to the tree, but yearly infections will cause reduced growth and may predispose the tree to other stresses.

Control Options

Disease control measures for different trees vary slightly because the period of infection is different depending on the fungal species involved. If fungicides are used, sprays must be applied on a preventative basis, beginning before infection takes place. Spraying large trees for many anthracnose diseases may be impractical and unnecessary, especially in dry springs. Sanitation is important in reducing the amount of fungal inoculum available for new infections. For large, high-value sycamores and other trees, micro injection with fungicides is another option.