University of Illinois

No. 15/July 3, 1997

Anthracnose Leaf Blight of Corn

We have received several calls relating to the presence of anthracnose on corn during the early season growth period. Anthracnose is a common leaf pathogen in young corn and is favored by frequent rainy periods, presence of previous corn crop residue, and other factors.

Anthracnose of corn, caused by the fungus Colletotrichum graminicola, overwinters in corn debris. With the acceptance of reduced tillage in many fields, incidence of anthracnose has begun to increase. Plowing and burying of all previous corn residues reduces the overwintering potential for this fungus and the early season leaf blighting now common in many Illinois corn fields. Consideration should be made for erosion possibilities because other control measures are also available.

Spores from corn debris are carried by wind or splashing rains to the lower leaves of young plants, where initial infections occur. As the disease progresses through its life cycle, additional spores are released and the cycle repeats itself.

Symptoms of anthracnose leaf blight begin as small oval-to-elongate spots that have a water-soaked appearance. As lesions enlarge, they may coalesce, and blighting of the entire leaf can occur. Black fruiting structures known as acervuli may develop abundantly within the lesions.

Most of the calls we're getting concern whether or not the disease will affect yields and crop growth. The answer is no. Anthracnose leaf blight is a common problem when corn is in the 1- to 4-leaf stage. Blighting may be observed on the lower leaves but ceases when plants reach the 6-leaf or older stage. At this time, the plants begin producing compounds known as phenols, which inhibit the development of this fungus; and the leaf blighting disappears. Thus, only the bottom few leaves are affected, with the possible exception of a few highly susceptible inbreds. There will be differences among hybrids, so if more than a single hybrid is planted on a farm, producers may observe differences in blighting.

A note of caution is needed here. Fields where corn follows corn are the most likely to have anthracnose problems, which may include a stalk rot late in the season. No-till continuous corn is an excellent location to test your hybrids for anthracnose resistance. Fortunately, dent corn hybrids have adequate leaf blight resistance, so this phase of the disease is usually not a serious problem.

If you notice anthracnose problems now, make a note because these fields may develop the stalk rot phase of this disease at the end of the season. Anthracnose stalk rot can be a serious problem over much of Illinois. Although there are no accurate predictive methods for stalk rots at this time, they generally appear when any stress conditions occur. Cloudy and rainy weather, insect infestations, poor soil fertility, and similar factors can increase the possibility of stalk rots.
H. Walker Kirby, Extension Plant Pathology, (217)333-8414