Dollar Spot Control

Dollar spot is caused by a fungal pathogen (Sclerotinia homoecarpa) that blights leaf tissues, according to Rick Latin, professor of plant pathology, Purdue University, West Lafayette, Ind. "It is not likely to kill the grass because it doesn’t go down into the crowns," he explained. "It will certainly make it appear like low-quality turf. When you have that, there’s probably a lot of chlorosis (yellowing or whitening of normally green plant tissue) around the turf stem."

According to Latin, initial symptoms of dollar spot include small lesions on the grass blades (usually apparent only on taller mown turf), shaped like an hourglass with reddish-brown margins. Mycelium that looks like spider webs or cotton candy is also often visible on humid mornings after long dew periods, he said.

Dollar spot is currently prevalent throughout the Midwest as conditions have been right for the disease. "I would say weather-wise, especially lately, the threat has certainly been there, and I look for it to increase as the temperatures increase here over the next few days," Latin noted. He said moderate temperatures, like nighttime temperatures between 55 and 65 degrees, and periods of higher moisture make conditions pretty favorable for dollar spot.

"The most important weather determinant for dollar spot infection is the combination of the length of the dew period, usually at night, and the temperature during that dew period," Latin explained. He has noticed a recent period of higher moisture in Indiana with lower temperatures, and the temperature on Tuesday was about 63 degrees. "I think conditions are prime right now for dollar spot," he said.

EARLY DOLLAR SPOT CONTROL. Severe outbreaks of dollar spot generally indicate an area is nitrogen-deficient, said Latin. A standard fertilization in May of 0.75 to 1 pound of nitrogen (N) per 1,000 square feet with a primarily slow-release nitrogen should help to minimize dollar spot by late spring, he added.

However, Latin said, "Dollar spot control in a home lawn situation really begins in the fall. If we have proper nitrogen fertilization, I seriously doubt dollar spot will be much of a problem. Now, if we do have a problem with dollar spot in June and July, it probably signals that the lawn is deficient in nitrogen and a little spoon feeding might not hurt."

If that situation occurs, Latin recommended using 0.75 or 0.5 pounds of nitrogen per 1,000 square feet to spur the turf to grow a little better before its growth slows in the hotter summer months. "A little bit of extra nitrogen will certainly help it along quite a bit," he noted. "Then, getting back into late summer and early fall, a great nitrogen program should prevent dollar spot from occurring or becoming a problem."

Fungicidal control is also an option to help reduce dollar spot, especially on larger commercial properties. He recommended using DMI (demethylation inhibitor) fungicides to fight the disease. "They can be very effective," he concluded. "They can knock dollar spot down very quickly, and that combined with a little bit of nitrogen will really bring the turf back into a very healthy state quickly."