Degree-day programs

In the past, recommended plant growth regulator (PGR) programs have been based on calendars, says Dr. Bill Kreuser, assistant professor of agronomy and horticulture at the University of Nebraska, Lincoln.

"In the early 2000s, people applied every two weeks, which is fine during cool weather," he says. "But as it gets hotter during summer months, PGRs are broken down in the plant faster and they don't sustain that growth suppression for the full two weeks."
   
Currently, Kreuser is working with SePRO and other companies to develop degree-day models to predict when a PGR wears off. "The goal is to make applications before that date occurs so we can maintain growth suppression and have sustained plant health and other benefits all year long," he explains.

The University of Nebraska's Greenkeeper app automatically keeps track of product efficacy, including PGR breakdown, and notifies superintendents when control has expired for one of your products. Visit www.greenkeeperapp.com to sign up.
   
"Messing around with application rates has minimal impact on how long the PGRs last," adds Kreuser. "It really comes down to this:  if it's hot, apply more frequently and if it's cold, apply less frequently."
   
Dr. Jeff Atkinson, Portfolio Leader Turf & Landscape Solutions, SePRO Corp., encourages superintendents to use the degree-day models to understand the differences between PGRs in terms of appropriate application intervals for each PGR.  In addition, he suggests talking to neighbors, peers, regional university and extension specialists, and local company field representatives about conditions in their regions.

"There's a wealth of knowledge about any given area," Atkinson adds. "You just need to tap into it."

Deborah S. Clayton is a freelance writer based in Ambler, Pa., and a frequent GCI contributor.