Dollar spot of turfgrass
Dollar spot, a fungi that infects turfgrass, gets its name from the silver-dollar-sized spots it forms on closely mowed bent grass, like the grass found on a golf course green. On lawns, however, the fungi may infect larger areas in just a few days. Patches may coalesce to encompass several square feet. In Colorado, dollar spot affects Kentucky bluegrass, annual bluegrass, Bermuda grass, fine-leaf fescues, perennial ryegrass and zoysia grass.
To determine the presence of dollar spot, inspect an individual blade of grass from a healthy looking part of the lawn. Then select a blade from an area just outside of a dead-looking patch of grass. Inspect the individual grass blades for a white lesion or spot that is pinched in the middle and looks like an hourglass. The lesion often occurs in the mid-section of the leaf blade and may have a purple margin. This bleached, hourglass-shaped lesion is characteristic of dollar spot.
Dollar spot is especially active during hot, humid weather and when leaf blades are wet for prolonged periods of time. A stressed lawn is more susceptible to the disease than a properly maintained lawn. When dollar spot infects a lawn that's stressed due to soil compaction, heavy thatch, improper fertilization or insect damage, a fungicide won't solve the problem.
Proper lawn care is the key to managing dollar spot. A compacted or heavily thatched lawn may require core aeration. Proper irrigation also is important. Water between 9 PM and 8 AM, so watering corresponds with -but doesn't extend -the natural dew period. It's important to minimize leaf wetness as much as possible. If you mistake dollar spot for an under-watered lawn, when in fact the lawn is over-watered, the disease may get much worse.
When planting new turfgrass, choose varieties that are resistant to dollar spot, if they're available in your area. But don't choose a particular variety only for that reason. It's best to seed or sod with a mix of two or more turf varieties that have desirable characteristics.
Dollar-spot fungi have developed varying degrees of tolerance to fungicides, so use them only as a last resort. As with any chemical, be sure to read and follow label instructions.
For more information, see the following Colorado State University Extension fact sheet(s).
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Updated Tuesday, November 19, 2013