Anthracnose symptoms on poa.
Anthracnose is particularly damaging to annual bluegrass (occurs almost any time of the year) and bentgrass (generally occurs in the summer or early autumn).
Foliar blight symptoms include a yellowing or reddish-brown discoloration of leaves. Loss of shoot density results in irregularly-shaped, yellow-bronze patches which range in size from a few inches to 2 feet or more. Minute, black, spiny cushions (acervuli) form on dead and dying leaves, sheaths, and stems which can be seen with a 10X hand lens.
With warm to hot weather, turfgrass affected by basal rot initially turns yellow or reddish brown in irregularly-shaped patches several feet or more in diameter. Within an affected patch, the disease may be spotty rather than affecting the entire area. In advanced stages of basal rot, close examination of the affected stem bases and stolons will reveal rotted tissue as well as acervuli on dead and dying leaves, sheaths and stems.
Anthracnose is known to occur as two phases: foliar blight and basal rot (of the crowns, stolons, and roots). The foliar blight phase generally occurs during periods of high temperature (80 to95 F) stress combined with prolonged periods of leaf wetness. Basal rot occurs on annual bluegrass in cool (spring) to hot conditions, but only occurs on bentgrass during warm to hot weather.
Stress factors necessary for infection include high temperature, low mowing height, compaction, inadequate soil moisture and nitrogen, and mechanical injury. High humidity and canopy moisture also promote infection.
Follow good cultural practices for the turfgrass species you are growing to promote steady growth and to alleviate the stress factors listed above. In particular, the following practices are most beneficial: 1) water deeply and infrequently, but syringe (brief, mid-day sprinkling during very hot days) and core aerify and/or apply wetting agents as needed to reduce stress due to compaction and localized dry spot, 2) maintain balanced and adequate fertility using light and frequent applications, 3) increase the mowing height as high as the turf species and use will allow, and 4) Avoid topdressing during periods of turfgrass stress and anthracnose development.
There may be little or no response to fungicides applied after the disease appears, particularly on annual bluegrass on golf greens. Where the disease is a chronic problem despite proper cultural practices, preventive applications of fungicides may be justified to help the turfgrass survive stressful periods.