Lawn & Turf Tips:  Summer Patch

Summer Patch (Magnaporthe Poae)

Disease Description

Kentucky bluegrass and annual bluegrass tend to be the most susceptible grasses when it comes to

Summer Patch.  It first appears as wilted, dark-green, and roughly circular areas of turf 1-2" in diameter. You may see healthy turf in the center of the circle giving it a ringed or "frog-eye" look. As the disease, progresses, the affected grass soon turns to a straw-brown color, leaving patches that initially resemble dollar spot disease.  The patches increase in size and may even take on a crescent shape, elongated streaks, or circular patches.  You may notice that the outer edge of the patches may have a yellow or bronze appearance with the leaves dying back from the tips.

Predisposing factors

The environmental factors are key to the development of summer patch are:

• It tends to be more sever in the summer occurring during July and August.
• Symptoms may appear during early July when the day time temperatures are consistently over 90 degrees F. 
• The soil Temperatures are over 78 degrees F in the root zone and soils are moist.
• Wet summers with moderate temperatures can delay the symptoms until August or Early September.
• Its activity declines as the temperatures become cooler in mid to late September.
• Heavy Spring Applications of high Nitrogen fertilizer applications.
• An accumulation of thatch and frequent irrigation or rainfall.
• Low mowing (mowing the grass too short) is the biggest contributor to the severity of the disease. Scalping lawns by mowing too low after allowing the turf to grow tall can trigger the appearance of the disease.

Cultural Control

There are several things that can be done to aid in relieving the turf stress:

• Core aeration or deep tine aeration in the fall and spring. This promotes deep rooting, resulting in healthier turf that's less prone to infection and more tolerant of summer stresses despite mild, or even moderate levels of infection.
• Avoid watering at night.  The cool night time temperatures and lack of absorption tend to promote fungus activity.
• Maintaining a balanced fertility program
• Keep mowing height at 3 1/2" - 4" high to alleviate the turf stress that occurs when it is mowed to short.  Turf mowed too short promotes fungal activity.