The fungus pathogen causing dollar spot was previously known as Sclerotinia homoeocarpa. Dollar spot fungi now are considered species of Lanzia and Moellerodiscus.

Dollar spot initially was a major concern on bentgrass where it forms spots the size of silver dollars, hence the name "dollar spot." However, on Kentucky bluegrass lawns the fungi may infect large areas in just a few days. Infected areas 4 inches or larger may run together, causing large patches. Irregular patches to 12 feet wide are not uncommon on bluegrass lawns. In Colorado, this disease complex also can be a problem on annual bluegrass, bermudagrass, fine-leaf fescues, perennial ryegrass and zoysiagrass.

Dollar spot fungi may be spread by mowers, traveling sprinklers and other maintenance equipment. Maintaining clean equipment may help prevent spreading. Strains of dollar spot fungi grow within a wide range of temperatures, so this turf disease may be active from late spring to late autumn. However, most problems occur when temperatures are moderately warm and change rapidly, as with warm days and cool nights. Because this disease complex often is serious on bluegrass and other turf during hot weather, many homeowners feel the resulting bleached grass is caused by a lack of water. They don't realize the problem is caused by fungi. Overwatering in an attempt to correct the supposed drought may make the disease get much worse.IdentificationAt first, affected leaves show yellow-green blotches or bands that normally go undetected. These lesions gradually bleach to a white or straw color. On finer-textured turfgrasses, individual lesions on the leaves often span the width of the grass blade, producing a constricted area resembling an hourglass. On coarser grasses, the spots caused by dollar spot may not span the blade. Leaves infected by Ascochyta usually start dying back from the tips. Lesions caused by Ascochyta leaf blight, which occur in the middle of a blade, usually do not have a hourglass shape or a border area between the white, dead tissue and the green, healthy tissue. See fact sheet 2.901, Ascochyta Leaf Blight of Turf, for more information on this disease. Individual leaf blades may have a single lesion or many small lesions or be entirely blighted. Infected blades usually have a distinctive tan to purplish streak between the white and green portions of the blade. These white-banded blades are most evident between dead areas and green turf. The tip of the leaf blade may show the characteristic lesion, or the lesion may be in the middle of the blade, leaving the leaf tip green. When grass is wet from early morning dew, a fine, white cobweb-like mycelial growth (strands of fungus) may be visible on diseased leaves. As the grass dries, the mycelium disappears. Do not confuse this with spider webs or the downy seed tufts of cottonwood trees.

Stress Factors
Turfgrass under stress is more susceptible to dollar spot than is properly maintained turf. Low nitrogen fertility, improper mowing (frequency and height), excessive soluble salt (alkali) levels, and improper watering all make turf more susceptible to disease. Newly sodded or seeded lawns that receive heavy watering also are frequently attacked. Because of root loss, turf damaged by white grubs or billbugs may need to be watered daily like newly laid sod. This type of treatment may increase the severity of dollar spot and require application of an appropriate fungicide. Long periods of high humidity or free moisture within the foliar canopy may cause severe outbreaks. Watering turf at the wrong time may extend this susceptible period and increase the incidence of disease. Heavy thatch layers may promote dollar spot because water, air and nutrients cannot penetrate to the underlying soil and grass roots. This results in shallow and poorly developed roots that are quite susceptible to drought stress. Thatch also ties up and reduces the effectiveness of pesticides.

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