ANR-1049, New July 1997. By Austin Hagan, Extension Plant Pathologist, Professor, and Jacqueline Mullen, Extension Plant Pathologist and Diagnostician, both in Plant Pathology at Auburn University.

Plant Disease Notes Anthracnose On Maple And Oak

On oak, the fungus Apiognomonia quercia is the most common causal agent of anthracnose but other species may also damage trees. Although the chestnut, live Shumard, scarlet, willow, pin, post, southern red, water, and laurel oak may be damaged, white oak is considered most susceptible to anthracnose. Symptoms on the young leaves and shoots include browning and shriveling of the blighted tissues. The ends of blighted leaves often are curled or twisted. Mature leaves usually suffer very little damage. Typically, blighting of the leaves begins on lower branches and spreads upward through the tree canopy. On laurel, pin, Shumard, water and willow oak, a second anthracnose disease, which is characterized by numerous tiny brown to black leaf spots often with a yellow halo, may also occur. The center of the spots may fall out of pin and Shumard oak leaves.

Persistence And Transmission. Anthracnose fungi overwinter in twig cankers or on fallen leaves. Spores are splashed by wind-driven rain during the spring to the new leaves and shoots. If the leaves remain wet for more than a few hours, infection will occur. Several consecutive days of mild, humid, wet weather in the spring favors outbreaks of anthracnose. As weather conditions get hotter and dryer in late spring and early summer, disease development slows.

Control. In landscape plantings, anthracnose rarely threatens the health of mature maples and oaks. Anthracnose is best controlled by using the following strategies:

• Gather fallen leaves before the trees leaf-out in the spring and either discard or compost.
• Fertilize and irrigate trees that have suffered considerable foliar blighting and defoliation.
• Apply fungicide on newly planted or small specimen trees such as Japanese maple previously damaged by anthracnose. Fungicide treatments can give effective disease control. For best results, make the first application as the trees begin to leaf-out in early spring. Additional sprays should be applied at 10- to 14-day intervals until the new leaves mature. On maple and oak, bordeaux mixture, Daconil 2787 4F, Daconil Ultrex, Dithane T/O, Fore, Protect T/O, 3336 50W, 3336 4.5F, and Halt are among the fungicides labeled for control of anthracnose. Always refer to the label for use rates, directions, and precautions before applying any fungicide.

For additional information, see ANR-500B, Alabama Pest Management Handbook--Volume 2.

The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a registration is changed or canceled, the rate listed here is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information.

Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.

For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.