Anthracnose Control on Annual Bluegrass

Causal Agent

• The fungal disease is caused by Colletotrichum cereale. Though fungal growth is most active during warm weather conditions, it is likely to infect grasses at any time of the year. Poor cultural management of turfgrass is among the frequent causes of the disorder. These include poor fertilization, very low mowing height, drought and excessive shade. Annual bluegrass turf that is already under stress tends to be affected very severely.

Symptoms

• Anthracnose is characterized by the appearance of yellow to brownish orange, ¼- to ½-inch-diameter spots on grass. Infection starts on older leaf blades and spreads throughout the grass. As the disease progresses, discoloration grows into larger-sized patches. When the fungus infects the leaf sheath, stem or crown of grass blades, the disease stage is referred to as basal stem rot. The lesions on grass blades at this time are initially water soaked, rapidly turning black as grass decays. Close examination of affected areas reveals black, fungal fruiting bodies that are spread with air and water to healthy grass areas.

Cultural Control

• Keeping lawns regularly fertilized with nitrogen throughout the year helps reduce chances of infection. The recommended annual rate of nitrogen is 3 lbs. per 1,000 square feet. During summer, apply 0.1 lbs. per 1,000 square feet every week to reduce chances of disease by 25 to 75 percent. The Kansas State University Extension recommends applying 0.5 lbs. of nitrogen per month per 1,000 square feet divided equally in weekly or biweekly applications. Avoid mowing grass at a very low height, as it is very hard to control or prevent the disease in short-mowed grass. Dethatch lawn regularly to prevent soil compaction. Do not overwater grass.

Chemical Control

• The use of chemicals for controlling anthracnose is most effective as a preventative strategy or the during the early stages of infection. Chemicals are not highly effective when used during the advanced stages of the disorder. When using chemicals, follow application instructions and apply at the recommended rates. Frequent applications of chemicals will not produce any better or rapid results. Recommended fungicides for anthracnose include azoxystrobin, chlorothalonil, fludioxonil, propiconazole or myclobutanil.