Summer Patch


Magnaporthe poae

Summer patch first appears in the warm weather of summer as yellow to bronze-colored, irregular-shaped patches ranging from 6 in. to 3 ft (15.3 cm to 1 m) in diameter. Patches may coalesce, resulting in areas of affected turf that are several feet in diameter. Annual bluegrass is the predominant host, and in mixed stands such as golf course greens, fairways and tees, a "frog-eye" symptom can be seen with creeping bentgrass remaining healthy. Dark "runner hyphae" is evident on crowns and roots of affected plants when observed microscopically.

The disease first appears in the warm weather of the summer, typically after rainy periods or heavy downpours. Saturated soils have been shown to exacerbate disease development. Soil temperatures above 70° F (21.1° C) at a 2 in. (5cm) depth for at least 48 hours are key for disease onset as well. While symptoms are present in the warm weather, infection takes place in the spring when soil temperatures first reach 65° F (18.3° C) at a 2 in. (5 cm) depth. Weakened roots from saturated, anoxygenic soil conditions allow for further infection and symptom development.

  • Crops Affected: turf


    The location of this disease is home lawns and golf courses. General symptoms are a circle, streak, wilted, and irregular coloring. Foliar symptoms are browning, and yellowing. This can occur during the months of July, August, and September. Hosts of the disease are Kentucky Bluegrass, Fine Fescue, and Annual Bluegrass.


    Fertility is an important management aspect for summer patch. Having adequate levels of all major soil nutrients can be determined by soil testing with the exception of nitrogen. Adequate levels of nitrogen are essential in managing summer patch. Moderate levels of nitrogen such as 0.5 lb of nitrogen per 1000 ft2 (0.25 kg per 100 m2) once a month are required for adequate summer patch management.

    Light, daily irrigation in amounts ranging from 0.1 to 0.4 in. (0.25 to 1.0 cm), depending on rainfall, temperature, and evapotranspiration, will help reduce the severity of summer patch. Irrigation timing should be scheduled in mid-late afternoon so as to allow adequate time for the turfgrass to dry before night fall. This practice helps to cool off plants during the warmest part of the day, allowing susceptible turf to better survive summer stress.

    Summer patch is best managed by chemicals preventively. Timing of these fungicide applications must be timed properly in order to be effective in controlling summer patch. DMI fungicides, triadimefon, myclobutanil, fenarimol, and propiconazole, and the QoI fungicide azoxystrobin are effective, but have to be applied before symptoms develop. Most recommendations are for an application when soil temperatures reach 65° F (18.3° C), with a second application made 30 days later. In problematic areas where summer heat lasts for more than three months, an additional application may have to be made 30 days later.