What Is Summer Patch & How To Treat It

Rated 4.9 Across 200+ Reviews


Summer patch is a destructive fungal disease that affects many cool-season grasses, particularly Kentucky bluegrass, annual bluegrass, and fine fescues. This disease can cause significant damage to lawns and turf, leading to unsightly patches and weakened grass. This article will explore what summer patch is, how it forms, its life cycle, and effective strategies for treatment and prevention.

What Is Summer Patch?

Summer patch is a common lawn disease caused by the soilborne fungus Magnaporthe poae. This pathogen infects the roots and crowns of susceptible grass species, leading to the development of circular or irregular patches of dead grass. The disease is most prevalent during hot, humid weather, typically appearing in late spring through early fall.

How Summer Patch Forms

Summer patch forms through a combination of environmental conditions and the presence of the fungal pathogen:

  • Environmental Conditions: The disease thrives in hot (above 85°F), humid conditions, especially when soil moisture is high. Poor drainage, compacted soil, and excessive thatch can exacerbate the problem by creating a conducive environment for fungal growth.
  • Pathogen Activity: The fungus infects the grass by colonizing the roots and crowns, obstructing water and nutrient uptake. This leads to weakened plants that are unable to survive the stress of high temperatures and drought conditions.
  • Symptoms: Initial symptoms include small, circular patches of wilted, discolored grass that eventually turn brown and die. The patches can expand and merge, forming larger areas of dead turf. A characteristic symptom is the presence of healthy grass tufts in the center of the dead patches, giving a "frog-eye" appearance.

Life Cycle Of Summer Patch

The life cycle of summer patch involves several stages:

  • Inoculation: The fungus resides in the soil and thatch, where it remains dormant during unfavorable conditions.
  • Infection: During periods of high temperature and moisture, the fungus becomes active and infects the roots and crowns of susceptible grass species.
  • Colonization: The fungus spreads through the root system, disrupting water and nutrient uptake. This leads to the development of visible symptoms on the turf.
  • Spread: The disease can spread through the movement of contaminated soil, water, or equipment. Spores produced by the fungus can also contribute to the spread.
  • Survival: The fungus survives in the soil and thatch during winter and other unfavorable conditions, ready to re-infect the grass when conditions become favorable again.

How Summer Patch Differs From Brown Patch

While both summer patch and brown patch (pictured above) are fungal diseases that affect turfgrass, there are key differences between them:

  • Pathogen: Summer patch is caused by Magnaporthe poae, while brown patch is caused by Rhizoctonia solani.
  • Host Preference: Summer patch primarily affects Kentucky bluegrass, annual bluegrass, and fine fescues. Brown patch affects a broader range of grasses, including tall fescue, perennial ryegrass, and bentgrass.
  • Symptoms: Summer patch forms circular or irregular patches with a "frog-eye" appearance. Brown patch typically forms large, irregular patches with a brown or tan color and a darker brown border.
  • Environmental Conditions: Summer patch thrives in hot, humid weather with high soil moisture. Brown patch is also favored by warm, humid conditions but can develop in a wider range of temperatures (60°F to 85°F).

Treatment & Prevention Of Summer Patch

Effective management of summer patch involves a combination of cultural practices, fungicide applications, and preventative measures:

Cultural Practices

  • Proper Mowing: Mow at the recommended height for the grass species to reduce stress on the turf.
  • Aeration: Aerate the soil to alleviate compaction and improve water and nutrient penetration.
  • Thatch Management: Regularly dethatch to reduce the thatch layer, which can harbor the fungus.
  • Water Management: Water deeply and infrequently to encourage deep root growth. Avoid overwatering and improve drainage to prevent waterlogged conditions.
  • Fertilization: Apply balanced fertilizer based on soil test results. Avoid excessive nitrogen, which can promote lush, susceptible growth.

Fungicide Applications

  • Preventative Treatments: Apply fungicides before symptoms appear, particularly during high risk periods (late spring to early fall). Fungicides containing azoxystrobin, propiconazole, or thiophanate-methyl are commonly used.
  • Curative Treatments: If symptoms are already present, fungicides can help limit the spread but may not fully eradicate the disease. Multiple applications may be necessary.

Preventative Measures

  • Resistant Varieties: Use grass varieties that are less susceptible to summer patch.
  • Good Cultural Practices: Maintain healthy turf through proper mowing, watering, and fertilization to reduce stress and increase disease resistance.
  • Sanitation: Clean and disinfect equipment to prevent the spread of the pathogen.

Summer patch is a challenging disease that can significantly impact the health and appearance of cool-season lawns. Proper cultural practices and timely fungicide applications can help manage summer patch and maintain a healthy, resilient lawn throughout the growing season. If you are dealing with summer patch or other lawn diseases in the Kansas City area, call Heartland Turf & Landscape today!