Anthracnose: Leaf Infecting Fungi


Many parts of the US experienced a very wet spring. Some areas also had to deal with cooler than normal temperatures making it prime conditions for leaf-infecting fungi. The results of the infections caused by these fungi are noticeable now, as leaves begin to fall or the leaves which are still on the trees are showing spots or lesions. These lesions often form along the leaf veins or on the edge or margins of leaves and can range in color from tan to reddish-brown to black.

The cause of these spots are from a group of fungi collectively called anthracnose. The disease can infect numerous tree and shrub species including Maples, Oaks, Sycamores, Ash, Birch, Viburnum and several other species. The symptoms include leaf spots and lesions, shoot blight, cankers on twigs, limb dieback and almost entire defoliation of the plant.

In many cases, even with defoliation, anthracnose does not cause permanent damage to the tree. Sycamores are one tree that can lose almost every leaf in late spring to early summer due to the disease and it will regrow a new set of leaves. This does put stress on the tree, but unless it happens several years in a row, the tree can recover from its loss of leaves.

Preventing Further Outbreaks

As with many foliar diseases, one of the keys to preventing further outbreaks is sanitation. This means raking up and disposing of infected leaves. The fungi overwinter in leaf buds, twigs, fruit, fallen leaves and even the leaf stems, or petioles, depending on the type of anthracnose fungi found on the tree.

The disease cycle begins in the spring during cool wet, weather with most activity peaking when temperatures are in the 50-70°F range. The spores from the previous year are dispersed short distances by water or long distances by the wind. The infection stage begins as the leaves are beginning to open in the spring. If the weather conditions remain or become cool and wet, the disease can re-infect the same plant in the summer. The cycle ends when the weather dries and the leaves mature.

Treatment for Anthracnose

For the most part, anthracnose has more of a cosmetic effect than permanent effect on most trees. If the tree is healthy and well-cared for, it can defend itself against anthracnose. Maintaining good tree vigor is important, which includes watering, adequate fertilization, mulching and proper pruning.

Many people fail to water their trees during drought periods. This is especially important on recently planted trees. Removing the grass from around the base of the tree in a circle of about 3 to 4 feet and replacing the grass with a 3 inch layer of mulch will provide numerous benefits to the trees and avoid possible trunk damage from lawn mowers and line trimmers.

Spring and fall fertilization is also very beneficial to the health of all your landscape plants. There are disease control materials that can be applied very early in the year as the buds are open, but this is not usually required unless the plant experiences the same problem with anthracnose every year.

The best thing to do is to have your landscape evaluated to determine a program that is the most beneficial for the health of your plants. Contact your neighborhood Lawn Care Professional at Spring-Green to have your landscape evaluated for disease and insect problems and receive a program that will help produce healthier landscape plants.