Friday, May 15, 2009
Dollar continues to be the most prolific disease in the Midwest. Dollar spot can cause damage to turfgrass for almost 7 months out of the year. Dollar spot can be controlled with fungicide applications and controlling nutrient levels in the soil.
Symptoms and Signs
On closely mowed turf, this disease appears as white or tan spots of dead turf about the size of a silver dollar. Hence the name dollar spot. These spots may run together, producing large areas of dead turf. Affected leaves initially show yellow-green blotches, which progress to a light straw color with a reddish-brown margin. Occasionally, white mycelium can be seen covering affected leaves in early morning on dew-covered grass. Dollar spot symptoms occur anytime from early to late summer. The disease usually reaches peak activity when air temperatures are in the 80° F range and under high humidity.
The fungus, Sclerotinia homoeocarpa, survives unfavorable periods as dormant mycelium in infected plants, therefore, fungal movement is brought about by equipment, people, animals, wind or water. When daytime temperatures reach 16°C to 27°C (60°F to 80°F) , the dormant mycelium resumes growth from the infected leaves to nearby healthy leaves, causing new infections. If night-time conditions become cool and dry soon after infection has occurred, or if control measures are exercised quickly, infection may not progress beyond scattered leaf lesions. If the grass is growing rapidly, the problems may disappear after one or two mowings. If favorable weather persists after infection such as warm nights, with dew forming on leaves, and if control is not achieved, entire grass plants may be killed and typical "dollar spots" may appear on the turf.
Late spring nitrogen-fertilizer applications can help to minimize dollar spot severity, since growth will be stimulated during the period (early summer) when dollar spot infection begins. Irrigate deeply, infrequently, and early in the morning to minimize moisture accumulation on leaves. Dew control on the leaf is a key agronomic technique that will help with the reduction in disease activity. This can be done with applications of wetting agents, removal dew by early morning mowing or by use of dew whips or squeegees.