These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Patch Disease in Lawns July 9, 1998 Hot weather of summer not only stresses us, it stresses lawns. Disease problems may become visible in hot weather. One example is the disease that used to be called fusarium blight, but is now known as either summer patch or necrotic ring spot. In addition, extended hot, humid weather with very warm nights may also favor brown patch. While heat and drought stress may cause lawns to brown, these patch diseases typically occur in distinct patterns. Look for crescent shaped or circular patches of dead grass, often with clumps of green grass inside (often called "frogeye"). Lawns with advanced disease development may show irregular dead areas and streaks. While hot summer weather may make the disease visible, lawns infected with summer patch or necrotic ring spot usually have some other underlying stress factors. Poor rooting is often involved. For example, a common scenario in our area is lawns sodded within the past 2 to 5 years over poorly prepared clay soil. Often these lawns are watered and fertilized heavily, which adds to the problem. Excessive thatch layers usually exist with these types of conditions. There is no quick cure to these diseases. Management should focus on correcting underlying soil and cultural practice problems as a long-term solution. Improving conditions for root growth and reducing excess thatch is critical. Core cultivation (aerifying) will help improve soil conditions and reduce thatch. Spring and fall are suggested times for aerifying, assuming the grass is actively growing. Overseed dead areas of your lawn with perennial ryegrass and resistant Kentucky bluegrass cultivars in late August or early September. Lawns need fertilization, but in moderation. Excess spring applications of nitrogen fertilizer may be a contributing factor to disease. Fertilizers containing controlled-release nitrogen are suggested. Early fall is a key time to fertilize. Finally, 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.

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