Nothing looks worse in an otherwise pristine, green lawn than those awful “dead spots” of yellow, dead grass. Spring dead spot is a common and serious disease of bermudagrass. With the right care and maintenance, however, you can eliminate the severity of those spots and help reduce the likelihood that they’ll return next year.
In Oklahoma, spring dead spot disease symptoms usually appear in April and May. Diseased areas are identified as circular dead patches of bermudagrass ranging from 3 inches to several feet in diameter. The circular areas can overlap to envelop a much larger area. Weeds such as crabgrass may begin to grow in the dead areas.
The causal fungus of spring dead spot attacks the roots, crowns, stolons and rhizomes of susceptible bermudagrasses in the fall, even though symptoms of infection cannot be seen from above. During these times, the fungus spreads radially through the soil, producing circular patches of infected grass. Infection in the fall is most devastating, since it is believed that the injury caused by the fungus predisposes the bermudagrass to winter-kill.
•Managing for prevention and recovery: Severity of spring dead spot can be reduced, though not necessarily cured, through proper turfgrass management. The rapid rate of spread of most bermudagrasses usually provides for complete recovery of the area if it is properly managed. Proper cultural practices not only aid in recovery of the affected areas, but also influence severity of the disease the following spring. Bermudagrass areas that are overfertilized in the fall as well as those having excessive thatch, poorly drained low spots, and highly compacted areas usually have the most severe symptoms.
• Clean-up and re-establishment: With no intervention, bermudagrass will often grow over the dead patches by late summer. However, recovery can be speeded up by raking debris from the patches, which allows stolons growing in from the sides to root more easily. In very large patches, placing plugs of healthy turf into the dead areas can help speed up recovery.
•Core aerification and dethatching: Core aerification of compacted sites may help to reduce the severity of the disease by providing improved root growth and thus a more healthy turf. Dethatch if thatch, when measured during the summer, exceeds 1/2 inch in thickness. Dethatching is best performed in late winter, prior to the greenup of bermudagrass and prior to application of pre-emergent herbicides.
•Grade and drainage: When necessary, fill or tile low areas to aid in surface and subsurface drainage. A uniform 2 percent slope will usually aid in providing good surface drainage. If adding soil, use a soil similar in physical characteristics to the existing top soil to avoid creating layering problems.
•Fertility: Adequate fertility is crucial to the development of a high-quality stand of bermudagrass and recovery from spring dead spot. Severity of the disease also can be reduced by avoiding heavy, late-season fertilization with quick-release sources of nitrogen such as urea or ammonium nitrate. Limit the last nitrogen application of the growing season for bermudagrass areas to about one pound of nitrogen per 1,000 square feet. Make this application no later than the first week of September.
•Fungicidal control: Fungicides need to be applied in the fall before the soil temperature drops to 70 degrees and a second application needs to be made 30 days later.
The following workshops will be at the OSU Extension Center, 930 N Portland. They are free and open to the public. Questions: call 713-1125.
• “Lawn Management”: 1:30 to 3 p.m. April 17.
• Third Thursday Gardening: “Vertical Gardening” — 6 to 7 p.m. April 17.