Red Thread and Dollar Spot Persist in Lawns

Last updated 8/6/03

HOME

TURF TIP
8/6/03

Red Thread and Dollar Spot Persist in Lawns

Red thread is persisting unusually long in Indiana lawns, primarily because of the relatively cool temperatures and frequent rains. Red thread first appears as small (quarter to golf ball size) gray – tan colored patches in the turf and can expand to 8" or more in diameter. Upon close inspection, characteristic red to coral colored "threads" (sclerotia) are often seen growing from tips of infected leaves. Dollar spot is also common in Indiana turf areas now and it first appears as small (1" diameter) patches of thin turf with bleached or straw-colored leaf blades within the patch. Careful inspection of affected turf may reveal distinct light tan lesions on grass blades. The lesions often have an hourglass shape with reddish brown margins. Fluffy white mycelium may be evident within the patches during early morning hours, after long periods of dew. These diseases usually indicate that the turf stand is nitrogen-starved. The excess growth from constant rain plus probably a little N leaching from excess rainfall sets up ideal conditions for these diseases. Most of the complaints are resulting from lawns where clippings are not returned, and this practice robs about 1 lb N/1000 ft2/yr from the turf. Though we don’t normally recommend August fertility, 0.5 lbs N/1000 ft2 applied now during our relatively cool weather should help with these diseases. Though fungicides easily control these diseases, fungicides are generally not recommended on home lawns. If a fungicide must be used, consider tank mixing with nitrogen to maximize control of dollar spot or red thread. Both dollar spot and red thread are most common on perennial ryegrass lawns, so avoid more than 10% perennial ryegrass in a seed mix when seeding a new turf area. More information can be found in Managing Lawn Diseases at http://www.agry.purdue.edu/turf/publicat.htm.

Rick Latin, Turfgrass Pathologist
Zac Reicher, Associate Professor/Turfgrass Extension Specialist