The Heat is On! – Turfgrass Science at Purdue University

The Heat is On!

Extreme heat is stressing turf areas quickly!

High temperatures cause turf decline

There are many causes of turf decline in the summer, but three primary physiological causes are 1) low photosynthesis rates at high temperatures, 2) lack of sufficient moisture, and 3) photorespiration. Photorespiration occurs instead of photosynthesis at temperatures above 87 °F causing cool-season grasses to use energy instead of making energy. As a result, cool-season grasses don’t make energy well when it is hot out and as a result they don’t grow (roots or shoots) well in hot weather which can lead to a decline in turf quality.

Lack of irrigation causing dormancy in some lawns

Water is critical to the growth of all plants, not just turfgrass. Water is a key part of photosynthesis and respiration reactions as well as many other plant metabolic activities. Turfgrass leaves and shoots are comprised of about 80% water. A lack or water (rainfall or irrigation) will lead to a decrease in growth due to a decrease in photosynthesis and plant respiration and an increase in plant temperature (lack of transpirational cooling; analogous to humans not being able to sweat). Each turf species responds to drought differently. Some grasses such as Kentucky bluegrass enter summer dormancy when soils begin to dry whereas others such as tall fescue can maintain their green color longer during drought.

How should turf be managed during dry spells and drought?

When possible stay off the turf! Limit traffic (including mowing) to minimize crushing of the turfgrass leaves and crowns and causing damage. In order to keep your lawn green during hot and dry periods at least 1.0 inch of water will need to be applied weekly. However, with far less water you can keep your lawn alive. Water once every 2-4 weeks with ½ inch of water to keep turf plant crowns hydrated during drought. This amount of water will not green up the turf, but it will increase its long-term survival during long dry spells.

When irrigating it is best to irrigate early in the morning, but occasional watering at mid-day or early in the morning in order to prevent injury from moisture stress is allowable. Following drought, turf should recover in 1-2 weeks after significant rainfall returns.

This year is looking very similar to last year. Hopefully we will not have extended periods of drought in 2011 and period rains will help keep turf alive and growing.

Damage from vehicle traffic on a drought stressed turf

Drought symptoms are visible right now.

Tall fescue clumps in a brown Kentucky bluegrass lawn under drought stress

Aaron Patton, Turfgrass Extension Specialist

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