Monday, July 14, 2008

Dollar Spot

Over the last several years, I have gradually seen an increase in the amount of Dollar Spot activity on the golf course. Having been in Colorado for nearly 20 years Dollar spot was virtually non existent, but as the local climate has changed so to has the occurrence of the disease.

We primarily see the Dollar Spot activity on the tees and also some select approach areas. It seems as if each year the number of infected areas grows and we now have to actually chemically treat some of the areas. In the past I have always been able to wait out the weather conditions that favor the development of fungal activity with out spraying, but that is no longer an option.

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.

Disease Cycle
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.

Cultural Control
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.


Graeme Taylor HGK St Andrews said...

Your comment about dollar spot being non existent until recently, is correlating, exactly with dollar spot occurrence in Scotland. It has only become evident in the last few years and is steadily progressing northwards each year. We also get it on tees first, however one green (fescue dominant) began showing signs last year. I like to try and develop natural immunity to diseases, but my agronomist has told me that dollar spot will get worse each year, and chemical control will be the only answer. We are not quite at the stage where I have to reach for the bottle, but it may be close.