Dealing with Active Summer Patch in Cool-Season Turf

Summer patch is a root-infecting disease with symptoms commonly evident as heat and drought stress increase. Best control is achieved with preventive fungicide applications in the spring, but there are steps that can be taken now to limit symptoms.
  • Infected grasses – Summer patch causes significant damage in annual bluegrass (Poa annua) and Kentucky bluegrass, but has recently been diagnosed in creeping bentgrass by numerous university diagnostic labs.
  • Pathogen activity begins in late spring – Summer patch becomes active at soil temperatures around 65°F, colonizing roots, and limiting water transport. Symptoms typically appear during early summer heat or drought stress when Poa annua starts to fade, typically leaving healthy creeping bentgrass behind.
  • What to look for – The first symptoms of summer patch include infected annual bluegrass turning yellow and thinning, often in circular or “frog-eye” patterns while the uninfected creeping bentgrass remains healthy.
  • Short-term cultural practices to minimize symptoms
    • Use acidifying fertilizers like ammonium sulfate when practical.
    • Do frequent hand-watering to limit stress.
    • Use frequent rolling to skip mowings and or raise mowing height.
    • Avoid excess stress from vertical mowing or dragging in topdressing.
    • Limit stress from other root pathogens like Pythium root rot and nematodes.
  • Fungicide programs
    • Fungicide applications should begin when 2" soil temperatures are at 65-68°F and continued on four-week intervals.
    • Applications after symptoms are seen can help to minimize future damage, but are much less effective than early preventive applications.
    • DMI fungicides are strongly preferred. Mirage® Stressgard® or Tartan® Stressgard will control summer patch plus have excellent summer safety on cool-season turf.
    • Water-in fungicides with 0.1 to 0.125" to move into upper root zone area of disease activity.
  • Need more info? – See the linked Bayer Solutions Guide or Zone Recommendations and contact your Bayer Area Sales Manager.

Summer patch causing yellowing and thinning in annual bluegrass, leaving the creeping bentgrass uninfected. Photo: Zac Reicher, Bayer.

  Bayer Solutions - Summer Patch - Cool Season
Paul Giordano

by Paul Giordano , Ph.D., Green Solutions Team Specialist

Monday, July 30, 2018