There is a good reason summer patch is called summer patch - the symptoms appear in the summer! However, Magnaporthe poae, the fungus that causes summer patch, is most active in spring when soil temperatures reach 65ºF. This is why the best time to apply fungicides for summer patch management is when soil temperatures reach approximately 65ºF for 3 consecutive days. The aim is to prevent the root damage that will result in symptom appearance later in the season.
How do you know when the soil temperature reaches 65ºF? One way is to buy a probe thermometer and insert it into the soil in the early afternoon at a depth of about 3-4 inches. Leave the probe in the soil for at least 5 minutes before reading the temperature. Another way is to follow UMass Extension’s Landscape Message: https://ag.umass.edu/landscape/landscape-message
Fungicide applications for summer patch are only necessary on turf that has a history of the disease. Drenches should be applied in enough water to carry the fungicide down into the turf root zone.
Most cases of summer patch on lawns can be alleviated without the use of fungicides. Fungicide applications in summer, after symptoms of summer patch have appeared, are generally ineffective on lawns. This is because high temperatures impede root and shoot growth, resulting in slow turf recovery. There are, however, several cultural management techniques that can be used to mitigate damage:
- Promote root development and reduce stress on the turf in any way possible.
- Avoid low mowing heights, especially during periods of heat stress.
- Avoid excessive nitrogen applications in spring. In summer, light application of nitrogen may help mask symptoms once they have developed.
- Maintain adequate fertility as determined by soil tests. Use acidifying fertilizers such as ammonium sulfate. Wash ammonium sulfate off leaves in warm temperatures to prevent foliar burn. Avoid the use of nitrate fertilizers which can intensify symptoms.
- Maintain soil pH between 5.5-6.0 (in situations where summer patch management is a priority)
- Annually, apply manganese sulfate at a rate of 2 lb/acre in the spring.
- The disease is most damaging in warm, saturated soil. Aerify to relieve compaction, improve soil drainage, and improve oxygen penetration into the soil. Water deeply and infrequently.
- Reseed affected areas with resistant cultivars of Kentucky bluegrass or perennial ryegrass. For best results, use mixtures or blends of resistant grasses.
Submitted by: Dr. Angela Madeiras