Anthracnose is somewhat of an oddity in the corn disease world because it is one of the few important diseases in the Midwest that can be a problem from the seedling stage of growth to harvest. The anthracnose pathogen can cause leaf blight of seedlings as well as late-season leaf blight, root rot, stalk rot, and top dieback, and it can infect stalks systemically. Incidence of this disease (particularly the late-season phases) has been reportedly increasing in Illinois, and it should be watched for. In some parts of Illinois, conditions are or may soon be favorable for the seedling leaf blight phase of anthracnose. |
Anthracnose was briefly described in the Bulletin on May 24, 2002, as one of a number of diseases that may affect corn seedlings, but this article will provide more detailed information on the seedling blight phase. Typical anthracnose lesions on seedlings are oval-shaped. They begin as water-soaked spots and may enlarge to 5/8" long, becoming tan with a reddish or yellow-colored border. Lesions may enlarge, grow together, and kill entire leaves. They typically are most common on lower leaves in the spring. Clusters of small, dark spines (setae) that can be seen with a hand lens will frequently develop in the dead tissues in lesions. It is important to note that symptoms may differ depending on weather conditions and age and genotype of the plant.
Anthracnose is caused by the fungal pathogen Colletotrichum graminicola. This fungus survives over winter on infected corn residue. It produces spores (inoculum) in wet weather, and the spores are spread by wind and rain to the new crop of corn seedlings. The Colletotrichum spores germinate in free water on leaf surfaces and penetrate through stomata or directly through the epidermis. The fungus then grows through the leaf tissue, releasing chemicals that disrupt the physiology of cells, resulting in cell death and lesion development.
Anthracnose on corn has increased throughout the Midwest in recent decades as conservation tillage has increased. Several other factors, in addition to infested corn residue, that favor anthracnose include warm temperatures (78-86 deg F), extended periods of high humidity, rain, and stress from other corn pests, such as root lesion nematodes and European corn borers. Seedlings (and mature plants) are most susceptible, because susceptibility is reduced when plants undergo rapid vegetative growth.
Management of anthracnose seedling blight is based on resistant hybrids. Most new hybrids are less susceptible to anthracnose than hybrids were 20 years ago; however, some hybrids may be available that are not as resistant as might be desired. It should also be noted that foliar and stalk rot resistance can be poorly correlated, and thus it is important to know which phase of anthracnose a hybrid is resistant to. Crop rotation and tillage may be acceptable practices in some areas to reduce inoculum for the seedling blight phase; however, these may be of minimal value for the stalk rot and late-season leaf blight phases and in areas where anthracnose is endemic. These management tactics will obviously not benefit the corn crop this year. However, they may warrant increased consideration next year, especially if scouting over the next few weeks reveals prevalent anthrac-nose in response to the warm temperatures and plentiful rain that has occurred recently in much of Illinois.--Dean Malvick