Summer Patch Fungicides

Summer patch is a root-infecting disease of Kentucky bluegrass, annual bluegrass, and fine fescues. Infection begins in spring, while visible patches usually appear during summer heat.

What to Look For

Yellow or bronze rings, arcs, and patches enlarge during hot weather and may form frog-eye patterns with green centers. Roots and crowns become dark and weak.

Why It Develops

Compaction, poor drainage, high soil pH, excessive thatch, low mowing, high spring nitrogen, and summer heat or drought stress increase damage.

Reduce Disease Pressure

• Aerify compacted soil and improve drainage.
• Maintain balanced fertility and avoid excessive spring nitrogen.
• Manage thatch and raise mowing height where practical.
• Use acidifying fertility cautiously where soil testing and local guidance support it.

What University Research and Extension Guidance Says

Kentucky reports that control is inconsistent and usually requires two to four preventive applications rather than one. Applications are timed by soil temperature while the root pathogen is active, and light irrigation after treatment can improve placement. Spring green-up applications made after the critical infection period did not improve recovery in cited research.

Choosing and Using a Fungicide

Use the products below as a starting point, then match the active ingredient, FRAC group, turf species, use site, timing, rate, interval, and watering directions to the current product label. Preventive or very early applications are usually more reliable than rescue treatments after extensive injury. Rotate effective FRAC groups and combine fungicides with the cultural changes above.

Research and label note: University research may identify useful activity even when a current product label does not name this disease. That is research evidence, not a label direction. Apply a product only where the turf or application site and use pattern are permitted, and follow the complete label and applicable state requirements.

University sources: University of Kentucky: Chemical Control of Turfgrass Diseases 2024.