With very little rain and recent daytime temperatures greater than 90 degrees, non-irrigated turfgrasses (like this zoysiagrass above) are showing signs of heat and drought stress. The initial visual symptom looks like dark spots in the lawn. This is due to leaf curling. The symptoms are most pronounced during the heat of the day. Often, the plant will re-hydrate overnight. During this extended drought, turfgrass plants in full-sun may not be able to re-hydrate. At that point the leaves will turn brown to tan. Those turfgrass areas that have some shade (trees, house, fence, etc) may be in better shape than areas that have full exposure all day. Just because the turf turns brown does not mean it is dead. This is the plant’s protection mechanism until ample water resumes. In terms of species, the response can be very similar as the drought persists. Tall fescue has suffered the most, followed by zoysiagrass, and then bermudagrass. We have studied tall fescue drought and found it can survive for an extended period despite its brown appearance. In one experiment conducted under a summer’s intense heat and drought, all our tall fescue cultivars tested recovered after 40 days without any water, and most survived 48 days without water. The grasses grew back from their crown when watering resumed. This is why we suggest dormant lawns are watered every three to four weeks with minimum water (0.5 inches) to keep the turf crowns hydration.
Our extension turfgrass specialists have been getting questions about suspending regular cultural practices during this drought. Turfgrasses under severe drought stress will need less frequent mowing. In the absence of irrigation, we have also seen far less disease pressure to date. Weed management can be a bit tricky. While the drought may reduce the occurrence of some weeds, the more open canopy of severely stressed turfgrass areas may increase others. As preemergence herbicides begin to break down, some postemergence control may be needed to maintain a weed-free lawn. However, postemergence efficacy can decrease on drought-stressed weeds. Fertilizer application is another tricky area. While we do not want to push a drought stressed turfgrass under severe drought, having some fertility available when we do get rain can aid its recovery. So, slow-release products may perform better over the recovery period as they would generally not be adding “salt to the wound” but still have some residual nutrition for the plant. Having a light base fertility can even improve recovery of a cool-season turfgrass such as tall fescue. In both cases, light nitrogen rates (no more than 0.5 pounds N per 1000 square feet) would be suggested.
The next consideration will soon be renovation of cool-season turfgrass areas as September will be here before we know it. I am hopeful that our rainfall frequency will improve by then so warm-season grasses will have a chance to fully recover before winter dormancy.
