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Dollar Spot on Turf Grass

bleaching of grass blades is a symptom of Dollar Spot

Pathogen
Dollar spot is caused by the fungus, Sclerotinia homoeocarpa. This fungus overwinters in stomata which may live for long periods on grass clippings, in thatch, or in soil. Favorable envriroments include temperatures between 60 and 85 degrees F and long periods of leaf wetness from dew, rain or sprinkler irrigation. Prolonged wet foliage is a key factor. Growth of the dollar spot fungus is inhibited when temperatures exceed 90 degrees F. The pathogens main transportation is by wind or water. Turfgrass growing under dry soil conditions is more susceptible than when adequate soil moisture is provided. Damage is usually more severe if there is a deficiency or great excess of nitrogen. Soil pH does not affect disease development.

Symptoms
The first symptoms of the disease appear as tiny yellow spots on individual grass blades. The spot expands to a straw colored or tan band with dark reddish-brown margins. The tip of the affected leaf often remains green. The tan band is narrower at the leaf and results in an hour glass like shape. Soon after bleaching then occurs. As the grass dies and the infected areas enlarge, light straw-colored spots 2 to 3 inches in diameter appear in the lawn. After this is detected another giveaway is a thin cob webby type structures are found in the infected areas early in the morning. This mycelial growth of the fungus will disappear as the turf dries. The turf in these spots may be killed all the way from the lesion to where the plant comes into contact with the soil. If undetected, the spots may merge and form large, irregular straw-colored patches. On golf greens and fairways, the spots are often well defined and smaller than those on high cut rough and as the name implies are about the size of a silver dollar. Thus, the descriptive term "dollar spot.'

Disease Management

Adequate fertilizer program. Utilizing proper Nitrogen fertiltity will greatly reduce the susceptibility. Careful consideration must be given to fertility programs to avoid excessive nitrogen fertility which aggravates other diseases such as Brown Patch.

Try to deter from long term leaf wetness. Avoid over watering and frequent late afternoon or evening irrigation that prolongs the time grass stays wet. This is especially true for mornings when heavy dew is likely. Prune trees and shrubs to facilitate optimal penetration of sunlight and remove barriers or wind blocks to promote optimal air movement so grass dries faster.

Irrigate turf during dry conditions. Provide adequate soil moisture for continuous and optimal turf growth.


Try selecting resistant cultivars. Before seeding, consider recommended cultivars that are resistant to dollar spot. This is especially helpful when planting Kentucky bluegrass.


Chemical control used early in disease development can be quite successful. Once dollar spot gains a foothold and is widespread, chemical management will be difficult.

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