Dollar Spot on Turfgrass

HYG-3075
Date: 
03/29/2010
Joseph W. Rimelspach, Todd E. Hicks, and Michael J. Boehm, Department of Plant Pathology

Dollar spot occurs on essentially all cultivated turfgrass species worldwide. In Ohio, it is primarily a concern on creeping bentgrass on golf courses and may be prevalent on bluegrass lawns. Dollar spot occurs from late spring to late fall and is most prominent after cool, moist weather.

Dollar spot on bluegrass showing fungal (mycelium) growth, in the morning while dew is still on the lawn. Hourglass-shaped tan lesions on bluegrass leaf blades.

Causal Organism

Dollar spot is caused by the fungus Sclerotinia homoeocarpa. This fungus produces resting bodies called stomata, which may live for long periods on grass clippings, in thatch, or in soil. The taxonomic classification of this fungus is currently under revision. Temperatures between 60 and 85 degrees F and long periods of leaf wetness from dew, rain, or sprinkler irrigation favor growth of this fungus. Prolonged wet foliage is a key factor. Growth of the dollar spot fungus is inhibited when temperatures exceed 90 degrees F. 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 of nitrogen.

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, or lesion, is often narrower in width than the leaf, resulting in the lesion taking on an "hourglass" shape. The entire blade soon becomes bleached. As the grass dies and the infected areas enlarge, light straw-colored spots 2 to 3 inches in diameter appear in the lawn. A fine, cobwebby white mycelium may be visible early in the morning when heavy dew is present. This mycelial growth of the fungus will disappear as the turf dries. The turf in these spots may be killed. If left unchecked, the spots may merge and form large, irregular, straw-colored patches. On golf greens and fairways, the spots are often well defined, 1–2 inches in diameter, and about the size of a silver dollar. Thus, the descriptive term "dollar spot."

Overall damage to Kentucky bluegrass lawn from dollar spot. Overall damage to creeping bentgrass golf green.

Management

  1. Genetic Host Resistance. Before seeding, consider recommended cultivars that are resistant to dollar spot. This is especially helpful when planting Kentucky bluegrass.
  2. Cultural Practices.
    1. Adequate fertilizer program. Proper nitrogen fertility will greatly reduce the occurrence and severity of dollar spot. Refer to OSU Extension fact sheet HYG-4006, "Fertilization of Lawns." Note: Careful consideration must be given to fertility programs to avoid excessive nitrogen fertility, which aggravates other diseases such as brown patch. 
    2. Avoid periods of prolonged leaf wetness. Avoid overwatering 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.
    3. Irrigate turf during dry conditions. Provide adequate soil moisture for continuous and optimal turf growth.
  3. Chemical Control. Used early in disease development, chemical treatment can be quite successful. Once dollar spot gains a foothold and is widespread, chemical management will be difficult. Please refer to OSU Extension Bulletin L-187, Management of Turfgrass Pests, for the most current recommendations for the management of dollar spot on turfgrass (turfdisease.osu.edu/publications).  
Program Area(s): 
Ohioline http://ohioline.osu.edu