Preparing Turf for Summer Stress
Tuesday, May 26, 2015
Written by Pam Sherratt, John Street, Ph.D. and Karl Danneberger, Ph.D.
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.
|Photo courtesy of Wes Ganobcik, Huntington Park|
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.