Soil temperatures in New England have warmed up very quickly in the past week. Soil temperatures can be used to schedule preventative fungicide applications, especially for root infecting fungi such as Magnaporthe poae (the pathogen that causes summer patch). Summer patch does not cause symptoms until after infection has occurred. Sustained periods of hot weather (daytime temperatures ranging from 82 to 95° F) in combination with heavy rainstorms are the most common time to observe disease symptoms, although the fungus is active in the spring and fall. Those who manage Poa annua putting greens and have experienced summer patch in the past are likely aware that preventative fungicide applications are critical. Preventative applications are only recommended if there has been a past history of summer patch at your site.
Sites with high pH levels (above 7) are more susceptible to summer patch. Therefore, the use of acidifying fertilizers (for example: ammonium sulfate or manganese sulfate) in the spring and fall when temperatures are cooler is recommended. Make sure to wash off turf if ammonium sulfate fertilizer is used and temperatures are above 80° F. Alkaline irrigation water can contribute to high soil pH and negate the effects of using acidifying fertilizer sources. Soil pH levels between 5.5-6 have shown to reduce summer patch severity. Nitrate N sources can increase soil pH and should be avoided if soil pH levels are above 7.
Warm, saturated soils are an important factor that favor root infection. Spring aerification will reduce soil compaction and introduce oxygen into the soil profile. Thus far we have seen plenty of saturated soils, however, soil temps have not quite been in the appropriate range for infection. Magnaporthe poae infection will begin when soil temps reach 65-70° F. Therefore, preventative fungicide applications should be made after the 5-day soil temp average of 65° F has been reached. These measurements should be taken at a 2-inch soil depth in mid-afternoon.
Fungicides from the DMI, QoI, and Benzimidazole classes are among the most effective for preventative control of summer patch and are listed in the links below. Applications should be made using a high spray volume (5 gallons/1,000 sq ft) or watered in with 0.1-0.125 inches of water directly following application. Avoid the use of growth regulators such as flurprimidol or paclobutrazole when applying high DMI rates, especially if temperatures are above 80° F. Preventative applications should be made within the next week since soil temperatures have just begun to consistently reach 65° F. Fungicide applications should resume in the fall where summer patch has been a problem.
If you suspect summer patch, please contact the UMass Extension Plant Diagnostic Lab for confirmation. You will receive a rapid diagnosis along with information about management strategies appropriate for your situation.
If you have questions about summer patch management, please contact the Turfgrass Pathology lab (firstname.lastname@example.org or 413-577-3303) and we would be happy to discuss your inquiries further.