Tech Notes Issue 8
Dollar Spot (Sclerotinia homoeocarpa) Can "Sneak Up" During Winter and Early Spring
With cooler temperatures of winter approaching, dollar spot under the right conditions can occur on both cool and slow growing warm season turfgrasses. On short cut cool season turf like putting greens dollar spot appears as small circular patches that can become sunken. Dollar spot can appear as small - the size of a fingertip - pitted spots to circular patches no larger than 5 cm in diameter. These patches however can coalesce when the disease is severe forming large blighted areas. Dollar spot is spread primarily by maintenance equipment and mowers, but can also be spread by shoes, and traffic activity.
If dew is present, the white cobweb- like mycelium of the pathogen (Sclerotinia homoeocarpa) is observed. As the leaves dry the mycelium disappears. Leaf lesions often appear as hour-glass shaped but can appear oblong or oval. The lesion appears a tan to
a bleached-out color with a brown border extending the entire width of the leaf. The brown or reddish border along the outer edge of the lesion is present on all cool season turfgrasses except on Poa annua. Dieback from the leaf tip can occur with the entire leaf becoming
blighted.
Dollar spot is most active within the temperature range of 15 to 30 C with high humidity and leaf wetness. In general, warm humid days, cool nights, and heavy dews are quite favourable for disease development. Although canopy moisture needs to be present, dollar spot is more severe on dry soils.
To reduce the severity of dollar spot maintain adequate soil moisture and fertility levels. Dollar spot is most severe on low or deficient nitrogen turf. Additionally, remove dew early in the morning through poling, dragging, or mowing. Removing dew reduces the wetting period necessary for disease development. For example, research has found that waiting to remove dew in mid-morning or for it to dry results in a greater amount of dollar spot than removing the dew in early morning.
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