Arkansas pasture managers, cattle producers and other growers may be noticing their
bermuda grass turning purple, and are trying to root out the cause, John Jennings,
extension forage specialist for the University of Arkansas System said.
“The evidence indicates that many cases involve well managed hay fields,” Jennings
said. “Many of these fields were treated for winter weeds and fertilized to support early
bermudagrass growth.”
In many cases, he said, no obvious insect problems have been reported. Soil fertility is
variable among cases, so from there, the evidence goes cold.
“Let’s examine the physiology of the victim: the bermudagrass itself,” Jennings said.
Bermudagrass is a warm season grass, which grows best at temperatures above 85
degrees. Green leaf tips always show up in March, especially when there is no burden
of winter weeds to block sunlight.
But it takes a series of consecutive warm nights above 60 degrees to get the internal
machinery of the grass working efficiently, Jennings said.
“Early on, the bermudagrass will start to grow on warm days, then gets shut down when
temperatures drop back,” he said. “Night temps in the 40s shut down growth for several
days. It’s a bit like trying to start a cold engine... it hits, sputters, hits, then finally starts
sluggishly.”
In late March and into early April, temperatures rose above 80 degrees. The warmer
temperatures likely prompted many producers to fertilize fields to push the
bermudagrass out of dormancy for early growth.
Temperatures then took a dive for several days, and warmed back up just before
Easter, Jennings said.
“It was as if spring had finally sprung, and then ‘blackberry winter’ hit right about
Easter,” he said, with temperatures dropping and frost occurring in northern areas of the
state.
“Blackberry winter is an old-timer saying referring to the often annual event, when spring
temperatures suddenly drop just about the time the blackberry briars start blooming,”
The tender growth of the bermudagrass, fueled by sunlight and fertilizer, suddenly
sputtered and stalled.
“Purpling” is caused by accumulation of anthocyanin pigments due to stress. It is
frequently associated with cold-weather-induced phosphorus deficiency. Plants normally
grow out of it when warmer weather arrives.
Jennings said the phenomenon brings several farming fundamentals to light:
- Controlling winter weeds is a good practice to allow more sunlight to reach the grass
and to warm the soil.
- Temperatures frequently turn cold sometime during late March and early April, which
can stress the plants being pushed out of dormancy early.
- Don’t apply nitrogen fertilizer too early in spring to warm season grasses. Wait for a
week of night temperatures with lows above 60 degrees.
