Dollar Spot of Creeping Bentgrass Putting Greens

Ned A. Tisserat
  Extension Specialist, Plant Pathology

Symptoms

 Dollar spot is the most common disease of creeping bentgrass on golf course fairways and putting greens. The disease results in the formation of small bleached spots that rarely exceed 2 inches in diameter. During favorable weather hundreds of spots may coalesce to blight large, irregular areas of the turfgrass. Severe dollar spot outbreaks result in a pock-marked or crater-like surface to putting greens. Individual infected leaves exhibit light tan lesions surrounded by a dark, reddish-brown border. These lesions may be difficult to see on closely mowed bentgrass without the aid of a handlens.

Figure 2 Dollar spot on creeping bentgrass.

Figure 1 Dollar spot on creeping bentgrass.

Symptoms

Dollar spot may develop throughout the growing season but is most common in spring through early summer and again in late summer through early fall. Disease development is favored by high relative humidity and extended periods of leaf wetness. Dry soils and poor nitrogen fertility also contribute to increased disease severity.

Control

Several of the newer bentgrass cultivars (Crenshaw, SR 1020, others) are very susceptible to dollar spot and should not be used for fairways or seeded on putting greens prone to the disease. Instead, use cultivars such as L-93 that are moderately resistant.

Several cultural practices will help suppress dollar spot. Minimize leaf wetness duration by physically removing dew (poling, mowing, syringing) in early morning and avoid early evening watering. Do not allow the grass to go under drought stress. Maintain adequate nitrogen fertility. Biological control of dollar spot by fertilization with composted turkey litter, bovine wastes and other organic amendments has been recommended by some turf managers. However, organic fertilizers have not consistently been shown to reduce dollar spot in university research trials. Similarly, the additional of microbial biological control agents (fungi and bacteria) have not been consistently shown to reduce dollar spot.

Preventive fungicide applications at 7- to 21-day intervals may be necessary to suppress dollar spot. Timing and frequency of application depends on weather conditions and on the type of fungicide that is applied. Continuous use of certain penetrant fungicides, including thiophanate methyl, iprodione and the sterol inhibiting fungicides (triadimefon, propiconazole, myclobutanil) may result in the selection and increase of fungicide-resistant strains of the dollar spot fungus. Superintendents should consider limiting the number of applications of these fungicides during the growing season and alternating these products with contact fungicides not prone to resistance problems.

Substituted aromatic

good

7-14

DMI

good

14-21

dicarboximide

good

10-14

Ethylene bis dithio carbamate

fair

5-10

DMI

excellent

14-28

DMI

excellent

14-28

Benzimidazole

good possible resistance problems, do not use alone

10-14

Dialk dithiocarbamate

Fair to good

7-10

DMI

excellent

14-28

dicarboximide

good

14

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Web updated 9/01/06
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