The ISU Plant & Insect Diagnostic Clinic has started to receive our first turf samples this season. It seems that the warm and humid weather conditions these past weeks have favored infection by a number of diseases on turf, including anthracnose.
Anthracnose on turf is caused by a fungus called Colletotrichum graminicola. This fungus is commonly found on dead or decaying organic matter, but when the conditions are right, it can cause foliar blight and basal rotting on almost all turf grass species.
Plants with foliar symptoms (foliar blight) sometimes show distinct leaf lesions, and as symptoms progress, older leaves may turn brown (Figure 1). When the fungus attacks the base of the plants, rotting and blackening of the crown (lower stem) may occur. Leaves will turn yellow and become water-soaked, but usually they won’t have any distinct leaf spots. When seen under a microscope, prickly cushion-like structures produced by the fungus (called acervuli) can be seen on infected tissues (Figure 2). Eventually, infected plants turn completely brown and die. From a distance, you may see yellow thinning patches with no definite shape (Figure 3).
Disease infection is favored by stressed out plants. Plants with root problems or reduced vigor make them an easy target for the fungus. Therefore, the best way to control this disease is by avoiding stressful conditions on your lawn. Make sure that your lawn is getting proper fertilization and avoid applying high nitrogen rates during dry periods or high temperatures. Improve drainage and when watering, water thoroughly but not too frequently. Also, increase mowing height and reduce mowing frequency.
Figure 1. Close-up of turf anthracnose symptoms (Photo by D.S. Settle, APSnet)
Figure 2. Cushion-like structures produced by the fungus on infected tissues (Photo by W. Beck)
Figure 3. Thinning yellow patches affected by turf anthracnose (Photo by D.S. Settle, APSnet)