DOLLAR SPOT

dollar spot leaf lesions on Kentucky bluegrass	Characteristic	Description
	Host Grass Species	all
	Month(s) with symptoms	February to November
	Stand Symptoms	spots, patches (4 to 12 inches)
	Foliar Symptoms - Location/Shape	round leaf spots, leaf lesions
	Foliar Symptoms - Color	tan or white
	Root/Crown Symptoms	none
	Fungal Signs	mycelium or none

 

Note: Still not sure if this is the right disease? The Turfgrass Disease Identification program may be helpful. Or consult the experts at the Turf Diagnostics Lab. Check the TurfFiles glossary for definitions of unfamiliar terms.

FACTORS AFFECTING DISEASE DEVELOPMENT

Dollar spot is most common in the spring and fall, when warm, humid days and cool nights lead to heavy dew formation. Dollar spot may develop when night temperatures exceed 50°F and the leaves are wet for 10 to 12 continuous hours. Extended periods of wet, overcast weather can lead to severe dollar spot epidemics on susceptible grasses. The disease can remain active throughout the summer, but activity slows when daytime highs consistently exceed 90°F.

Turfgrasses that are deficient in nutrients, especially nitrogen, are more prone to dollar spot and also recover from the damage more slowly than well-fertilized turf. The disease is also encouraged by drought stress, low mowing, excessive thatch accumulation, frequent irrigation, and low air movement. Certain cultivars are very susceptible to dollar spot while others are fairly tolerant.

CULTURAL CONTROL

Use of resistant cultivars is one of the most effective means of dollar spot management. This is particularly important for creeping bentgrass and Kentucky bluegrass, as cultivars vary widely in their susceptibility to the disease. Base turfgrass selection on regional cultivar trials and University recommendations, and plant blends and mixtures of cool-season grasses whenever possible.

Adequate nitrogen fertilization will help to prevent dollar spot, and will also encourage plants to recover quickly from the disease if it occurs. Select nitrogen sources, rates, and timings based on local University recommendations for your turfgrass species and climate. Use soil test results to apply the recommended amounts of phosphorus, potassium, lime, and micronutrients.

Dollar spot is encouraged by drought stress and leaf wetness. Proper irrigation timing is needed to balance these factors. Irrigate based on the moisture status of the soil, not on a calendar schedule. Use a soil probe to monitor the amount of moisture in the turfgrass root zone. Irrigate with sufficient water to wet the entire root zone, and then repeat when the entire root zone is no longer moist. Irrigation should be applied early in the morning, between midnight and 6 AM, to keep leaf wetness periods as short as possible. Mowing, dragging, or whipping the turf in the morning to remove dew can help to prevent dollar spot, but these practices can spread the disease if it is actively developing. Improve air movement and reduce humidity by pruning trees, clearing unwanted vegetation, or relocating desirable plants.

Excessive thatch accumulations greatly encourage dollar spot activity. Remove excess thatch by vertical mowing or power raking. Golf course putting greens should be aerified regularly and topdressed with sand to reduce thatch buildup.

Dollar spot is readily spread in leaf tissue or clippings from infected areas. Avoid spreading the disease by washing equipment before entering an uninfected area, by encouraging golfers to clean their shoes between rounds, and by removing and disposing of clippings taken from infected areas.

CHEMICAL CONTROL

Many fungicides control dollar spot, but preventative applications are most effective. A preventative program should be implemented in the early spring when night temperatures consistently exceed 50°F. When applied on a curative basis, fungicides must be applied at high rates and short application intervals.

Uniform spray coverage is important for maximizing fungicide performance; even small gaps in coverage may allow dollar spot to develop. Nozzle type, nozzle pressure, and dilution rate have the greatest impact on the uniformity of fungicide applications. Nozzles that produce coarse to extremely coarse droplets, such as TurfJet or Raindrop nozzles, dramatically reduce the performance of fungicides for dollar spot control. Air-induction or flat fan nozzles that produce fine to medium droplets are recommended. In order to provide thorough coverage of the turfgrass foliage, fungicides should be applied in 2 gallons of water per 1000 ft²; lower carrier volumes reduce the performance of fungicides for foliar disease control.

The fungus that causes dollar spot develops resistance to fungicides very quickly. To prevent or delay the onset of fungicide resistance, use integrated management to minimize fungicide use, rotate among fungicide classes after each application, and tank-mix systemic fungicides with a contact fungicide.