Infection by dollar spot fungus (Sclerotinia homeocarp) appears as tan or straw-colored spots ranging in size from a quarter to that of a silver dollar sunken in the turf. Occasionally, small cottony strings of the fungus can be seen growing from the diseased leaf blades.
Dollar spot occurs throughout the growing period, and is most active during moist, warm days and cool nights. As the disease progresses, individual spots may join to destroy large patches of lawn. It occurs widely on golf greens, but may also be a severe problem on lawns growing under dry soil conditions.
Dollar spot damage is usually more severe if there is a deficiency of nitrogen. Disease fungi are spread from one area to another by water, wind, mowers, other equipment or shoes.
Practices that promote healthy lawns help to reduce the occurrence of dollar spot. Mow lawns at the recommended maximum height. Try not to remove more than 1/3 of the leaf surface in any one mowing, and if possible, wash the mower between cuttings with a 10% bleach solution. Remove excess thatch and aerate compacted soils. Improve drainage by top-dressing with organic matter, such as organic compost or well-aged animal manure. Keep lawns well watered, but avoid sprinkling in the late afternoon or evening. Do not over water and apply a slow-release organic fertilizer high in nitrogen; applying liquid seaweed and chelated iron is also helpful. Do not overfertilize, since this can result in an increase of other turf grass diseases, such as brown patch. Over seed in fall with resistant turf cultivars. Dollar spot is rarely serious enough on home lawns to require fungicide applications.