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News & Press: OTF News

Preparing Turf for Summer Stress

Tuesday, May 26, 2015  
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Written by Pam Sherratt, John Street, Ph.D. and Karl Danneberger, Ph.D.

Photo courtesy of Wes Ganobcik, Huntington Park
The most stressful time of the year for cool-season turfgrass is typically June through August, when there are hot, sunny days and temperatures routinely in the 80s. The most common heat stress symptoms are a reduction in shoot growth and a stoppage or loss of a functional root system. Soil temperatures above the optimum are more detrimental than air temperature. When average daily soil temperatures exceed 70 degrees, 50 percent or more of the root system of a cool-season turfgrass can be lost. In a controlled study at Rutgers University, the researchers exposed creeping bentgrass plants to increasing soil temperatures while holding the air temperature constant at 68 degrees. At temperatures above 70 degrees they observed a decline in root mass, length and activity, which continued to decline with increasing soil temperature. In Ohio State rhizotron research, root activity and growth declined dramatically during summer stress.

Leading into the summer stress period, it’s important to encourage as much root, rhizome and stolon growth as possible. Exposing turf to drought stress prior to the summer stress period, called "drought preconditioning”, can enhance the turf’s ability to withstand heat and drought stress. Research has shown that drought preconditioning can promote deeper and more extensive root systems in turf like Kentucky bluegrass. In addition to deeper roots, preconditioned plants maintained greater leaf water content and enhanced stomatal conductance and transpiration rates. Physiologically, drought pre-conditioned plants tend to accumulate ion solutes, specifically potassium, at higher levels during periods of high temperature stress compared to non-drought stress plants. The higher ion concentration allows for a relative higher osmotic adjustment potential during summer stress. Preconditioning is done by exposing the turf to mild drought stress in the spring, which can be a challenge if there are heavy rain events throughout the spring months.

In addition to pre-stress conditioning, it is essential to carry out cultural practices that alleviate soil compaction and improve drainage, since spring is the best root growing period for cool-season grasses. Soil cultivation through coring or spiking will enhance gas exchange and help to remove excess water from spring rains. In spring it is important to be judicious with both water and fertilizer applications. Excessive amounts of nitrogen will favor top growth and be detrimental to root growth, so light rates of fertilizer are favored. Potassium is the nutrient most associated with water regulation within the turf plant, and it has been linked with increased stress tolerance and improved injury recovery, particularly in warm-season grasses.

The combination of pre-stress conditioning and cultural practices to encourage root growth at this time of year will provide great dividends during summer stress. Turf with healthy roots will be more likely to endure problems like white grub attack and summer patch disease, as well as foot traffic and drought.

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