Anthracnose on silver maple.
|Severity:||2 out of 5|
|Frequency:||3 out of 5|
Spots or irregular necrotic areas appear on the leaves and twigs (sycamore, oak, dogwood) of infected trees in late spring and early summer. On some species, the necrosis follows along veins. In wet weather, the new growth becomes infected and may develop curled or distorted leaves. Symptoms can look similar to frost injury, which often occurs at the same time. On sycamore, anthracnose fungi also cause bud blight and branch cankers. Girdled stems die, producing a disfigured tree. In very wet years, premature defoliation is common.
Dogwood is affected by spot anthracnose (Elsinoe corni) as well as a much more serious disease called dogwood anthracnose (Discula sp.).
|Cycle:||Anthracnose fungi that infect only leaves overwinter on dead foliage on the ground. Cool, wet spring weather favors spore production and spread by wind and water to succulent new growth. Leaf lesions form, and spore production soon follows. Secondary cycles continue with cool, wet conditions. In a year with a cool, wet spring and early summer, infected trees often exhibit defoliation in June or early July. Anthracnose fungi that infect both stems and leaves overwinter in buds and bark and on cankers. Spores produced in the spring are splashed or blown to nearby leaves. The fungus can then grow into the petiole and eventually into the stem to form a stem canker. Secondary cycles of infection occur. Sycamore, oak, and dogwood have anthracnose diseases that infect leaves and stems.|
|Management:||Anthracnose diseases that infect only leaves rarely cause tree death but may cause early defoliation. A healthy tree will recover and refoliate with little permanent damage, so management practices are targeted at promoting tree vigor. An exception to this occurs with dogwood anthracnose, where stem cankers can girdle trunks and kill trees. If this disease is confirmed on a dogwood tree, removal of all infected plant parts, as well as applications of fungicides, are necessary. On most species, the removal and destruction of fallen leaves and major stem cankers reduce the potential for infection, but with oak and sycamore the cankers are so small and numerous that pruning is not possible. Fungicides are available to prevent anthracnose but are rarely recommended (except with dogwood [Discula] anthracnose) because of the cost of treating mature trees and because the disease is seldom fatal. If fungicides are used, they must be applied at bud break and reapplied, once or twice, at 10-14 day intervals to protect susceptible expanding leaf tissue. For oak and sycamore anthracnose, the first application should be made just before bud break. For large, high-value sycamore trees, the use of preventive injection fungicides is also an option.|