You Are Here: Management Updates 2000 Archive May 27, 2000

Date: May 27, 2000
Category: Diseases
Subject: Leaf Spot, Red Thread, Yellow Patch, Fusarium Patch, Basal-Rot Anthracnose

The continued rain has enhanced fungal activity and led to some confusing symptoms and signs. LEAF SPOT is rampant, especially in lawn grasses. It's easy for leaf spot to develop into melting-out when leaf spots accumulate and the fungus invades the crown of the plant. This is a distinct danger when plants are stressed, and the opportunity for that will occur this weekend when homeowners finally get a dry day to mow their much overgrown lawns. It has rained so much lately that it will be difficult to obey the "mow no more than 1/3 of the blade" rule. In lawns grasses, overseeding of thinned areas with disease-resistant cultivars is more effective than the use of fungicides.

RED THREAD is also widespread in lawns and golf courses, but it may be confusing to recognize. When conditions are very wet, the fungus may show mostly as a pink, gelatinous growth on leaf blades accompanied by tiny pink puffs of spores- with no "red threads" in sight. These will develop as the grass dries. The pink growths will become thinner and darker red. The pink stage may be confused with pink patch (which does not make pink puffs of spores or grow off the tips of blades) or even pink snow mold (Fusarium patch). In the absence of snow, pink snow mold makes greasy to coppery spots, but not usually the pink colored mycelium that is common at snow melt.

Where the weather is cooler, YELLOW PATCH (COOL-SEASON BROWN PATCH) and FUSARIUM PATCH (PINK SNOW MOLD) has been widely reported, but warmer weather is coming which should eliminate both diseases. Superintendents may want to read the Turf Tip regarding diagnosis of Fusarium Patch in the May/June issue of the USGA Green Section Record, pg. 22.

The first sample of ANTHRACNOSE CROWN OR BASAL ROT arrived at the diagnostic lab this week. It is most commonly associated with stressed annual bluegrass although bentgrass may also be infected. The continued moisture and temperature stresses have aided its appearance. Other factors associated with the disease are poor drainage, low nitrogen, low mowing heights, compaction and traffic. It is a difficult disease to control with fungicides. A combination of a DMI (e.g. Banner, Bayleton, Eagle, etc.) plus chlorothalonil are most effective. Crown-infected plants may not recover even after treatment, but the fungicides will at least protect the healthy plants. Diagnosis can sometimes be done by pulling plants straight out and looking for the charcoal black fungal structures in the crown of the plant. In the crown rot or basal rot stage, the acervuli with black hairlike setae may or may not be visible on the yellowing leaves. Be aware that the fungus produces masses of sticky spores that are easily tracked by feet and mowers. Wash mowers or modify mowing patterns to avoid spreading the fungus to nonaffected areas.

- Submitted by: Dr. Gail Schumann