It seems we have finally emerged from an unusually cold, wet April into an unusually warm spring. In light of this fact, it may seem premature to bring up the subject of “summer diseases”; however, now is the time to consider a preventive strategy. This is because the fungus that causes this disease actively infects turf during cool, wet weather. By the time symptoms appear when turf is stressed in mid-summer, the damage has already been done.
Summer patch can affect any kind of managed turf. Poa (bluegrass) is most susceptible to the disease, and fine fescues may also be affected. Symptoms appear as irregular yellow to tan patches that range from six inches to 3 feet in diameter. Smaller patches can coalesce and cover large areas. Patches sometimes have a “frog-eye” appearance as the centers are colonized by resistant turf species or cultivars.
Summer patch on lawn turf can usually be managed using cultural techniques, which enhance turf’s ability to withstand summer stress. Good cultural techniques include:
- Maintaining adequate fertility as determined by soil tests. Do not overfertilize. Use slowly available forms of nitrogen whenever possible. In areas with a history of summer patch, avoid the use of nitrate fertilizers, which can intensify symptoms.
- Maintaining soil pH around 6.0 or below. This can be accomplished with reduced liming on typically acidic New England soils, and/or the use acidifying fertilizers such as ammonium sulfate as nitrogen sources (wash ammonium sulfate off leaves with irrigation in warm temperatures to prevent foliar burn).
- Aerating annually to relieve compaction, improve soil drainage, and improve oxygen penetration into the soil.
- Watering deeply and infrequently. This encourages deep rooting, which helps turf endure heat and drought. Allow turf to dry down to the point of mild moisture stress between irrigation events.
- Avoiding low mowing heights (<3 inches), especially during periods of heat stress.
- Raking and reseeding affected areas with resistant cultivars of Kentucky bluegrass or perennial ryegrass. For best results, use mixtures or blends of resistant grasses.
Good cultural management practices are also critical for disease control on intensively managed golf and sports turf. Golf course superintendents also often employ a preventative spray program for summer patch where a history of summer patch exists or the probability of infection is high. The first fungicide application should be made when soil temperatures reach 65°F. Rotate among products with active ingredients from different FRAC groups.