Sclerotinia dollar spot is a fungal disease that affects most of the coolseason grasses such as bluegrass, ryegrass, fescue and bentgrass.
The overall symptom pattern for Sclerotinia dollar spot varies with mowing practices. Under close mowing (as on golf greens) the disease progresses from very small spots of dead turf to distinctly circular, straw-colored areas 2-3” in diameter, with a sharp margin outlined against the surrounding healthy grass. Patches may coalesce into larger irregular patches.
On higher mown turf typical of residential lawns, irregularly shaped, straw colored areas 1-6” diameter appear. Under ideal conditions, the patches may coalesce to cover large areas. When large areas are affected, the symptoms are often mistaken for drought injury.
Affected individual grass leaves first show yellow-green blotches that become water-soaked and finally bleach to a straw-color with reddish-brown margins. Lesions usually extend across the entire leaf, often have an hour-glass-shape, and dieback of the leaf from the tip to the lesion is common. When dew is present on the leaves, a cobwebby white, fungal growth may appear on infected leaves.
Sclerotinia homeocarpa, the causal fungus, overwinters in the crowns and roots of infected grass plants as mycelium (fungal threads) or thick-walled crusts of fungus termed stroma. The fungus is active from late spring through late autumn or early winter. When the temperature reaches 60°F, the fungus begins growing, reaching a peak of activity during humid weather with temperatures from 70°F to 86°F. The pathogen spreads to new areas primarily by transport of infected plant material with mowers, traveling irrigators, water, and other maintenance equipment. Grass growing under low soil moisture conditions is more susceptible than when adequate soil moisture is provided. Hence, severe outbreaks of the disease can and do occur during seasons of low rainfall. Dollar spot is less of a problem on turf growing in soil with adequate nitrogen fertility. Soil pH does not influence disease development.
- Cultural Practices - Maintain adequate to high nitrogen fertility: light and frequent nitrogen applications are recommended for disease management and maintenance of turfgrass growth. Water deeply and as infrequently as possible without causing moisture stress. Avoid irrigating in the late afternoon or evening as this prolongs overnight periods of leaf wetness and favors infection. Thatch should be maintained at no more than ½”. Do not mow wet grass. Provide good air circulation. Seed with resistant varieties.
- Chemical Control - Fungicide applications are made from June to September. Systemic fungicides provide good residual control. It is important to rotate classes of systemic fungicides. Optimum control using protectants is achieved when fungicide applications are made at frequent intervals during periods of disease outbreak.
- Biological Control - Biological control products are also registered for management of dollar spot. Consult your county Extension Educator or state Specialist for specific pesticide recommendations.
Stop! Read the label on every pesticide container each time before using the material. Pesticides must be applied only as directed on the label to be in compliance with the law. Contact the Division of Pesticide Control at (603) 271-3550 to check registration status. Dispose of empty containers safely, according to New Hampshire regulations.
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