Purdue turfgrass report: “In spite of a relatively cool summer, the extended heat this week may take a toll on cool-season grasses. These grasses are at their weakest point in the year with their lowest energy reserves, and thus their lowest tolerance to stresses like heat, drought, and pests. Minor disease infection with summer patch in Kentucky bluegrass or gray leaf spot in perennial ryegrass, minimal grub feeding in almost all grasses, or traffic in excess or at the hottest part of the day can cause significant damage. The good news is that day lengths are becoming shorter and the heat should not extend for too long into September.”
Considerations for turf health in late August heat:
On greens, consider skipping a day of mowing leaning instead to rolling. This maintains maximum photosynthetic area without sacrificing green speed.
Hold off on any fertilization until temperatures cool in September.
If the roots are very shallow, irrigate frequently and wet the soil only to the depth of rooting. This flies in the face of the “deep and infrequent” irrigation we normally recommend, but we may be soon be into damage control rather than sound turf management
Water early in the morning on other turf areas to limit disease pressure as much as possible
Syringe Poa annua in the afternoon to cool it slightly and increase its chances for survival
Preventative fungicide applications are recommended for high value areas, especially with high Poa annua or perennial ryegrass populations. Brown patch, pythium and gray leaf spot are the primary target disease right now.
White grub applications should already be applied but rescue applications with Dylox™ may be needed.
Though crabgrass and yellow nutsedge are flourishing, they are at the end of their life cycle and applications are not needed. Almost any herbicide can cause phytotoxicity once temperatures are >85F so avoid applications.
Limit topdressing, grooming, verticutting, dethatching or aerification until the weather moderates. If aerification is needed on greens, consider narrow, solid tines.
Minimize and restrict traffic where possible and change traffic patterns frequently.
If areas were seeded in the last two weeks, fungicides targeted for pythium/rhizoctonia should be applied to help protect the seedlings.
Zac Reicher, Professor of Turfgrass Science, firstname.lastname@example.org