These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.
Patch Diseases in Lawns
July 17, 1997
Major lawn disease problems of summer include the patch diseases; summer patch, necrotic ring spot, and brown patch. Summer patch and necrotic ring spot, which used to be called fusarium blight, attack roots of lawn grasses. Brown patch attacks lawns when prolonged heat and humidity exist, such as we saw in 1995.
These patch diseases are similar in appearance and management. Crescent shaped or circular patches of dead grass, often with clumps of green grass inside, are a characteristic symptom (often called "frogeye"). Lawns with advanced disease development may show irregular dead areas and streaks.
Patch diseases typically develop on lawns with underlying stress factors. One common situation in which these diseases occur is recently sodded lawns (within 2 - 5 years) put down over a clay soil, usually with good care (high watering & fertility) to keep the grass green and vigorous. This condition leads to poor root penetration and development, and also often a problem thatch layer.
Management of these diseases should focus on correcting soil problems and implementing proper cultural practices. Improving conditions for root growth and reducing problem thatch is critical. Practices such as core aerifying and topdressing, along with sound fertilizing, mowing (avoid mowing too short), and watering, are suggested. Light, frequent irrigation may help reduce stress of summer patch.
Core cultivation (aerifying) will help improve soil conditions and reduce thatch. Spring and fall are suggested times for aerifying, assuming turf is actively growing. Avoid heavy spring applications of nitrogen fertilizer. Focus most applications on the fall period. Fertilizers containing controlled-release nitrogen are suggested.
Overseed dead areas of Kentucky bluegrass stands with perennial ryegrass and resistant Kentucky bluegrass cultivars in late August or early September.
These management suggestions may not bring immediate results, but get patch diseases under control in the long run. Fungicides are an option to help prevent further development on unaffected grass, but will not reverse the factors causing the disease or eliminate the disease.
Also refer to Lawn Talk on this website.