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Annual Bluegrass

Poa Annua Suppression With Velocity Plus PGRs Requires Review of Weed Population

February 1, 2008 By: Steve McDonald TurfGrass Trends


Superintendents use a variety of chemicals to maintain fairways at the desired quality level. Some of these chemicals include plant growth regulators (PGRs) and herbicides (pre-emergent and postemergent). Two separate field trials were conducted during a two-year period to evaluate the impact of bispyribac-sodium (Velocity) herbicide treatments as impacted by pre-emergent herbicide and commonly used PGRs.

Velocity was released for sale in the autumn of 2004 and labeled for the control of Poa annua and Poa trivialis in creeping bentgrass (Agrostis stolonifera) and perennial ryegrass (Lolium perenne) fairway turf. Research shows that Velocity has the potential for Poa annua and Poa trivialis management, and the optimal application timing might be when average ambient air temperatures are 65° Fahrenheit. Golf course superintendents frequently apply other herbicides and plant growth regulators prior to and following this time frame. Information regarding possible interactions of these chemicals with Velocity is warranted.

The purpose of Study 1 was to evaluate the effects of pre-treatments of a commonly used grassy weed herbicide and two plant growth regulators for their impacts on Poa annua control.

One of the main issues with using Velocity to control Poa annua and Poa trivialis is the voids created by removing the grassy weeds during the golf playing season (Photo 1). Therefore, the purpose of Study 2 was to evaluate the effects of season-long PGR programs for the ability of Velocity to control Poa annua and the impact on the resulting voids from the declining Poa annua. Other factors evaluated in each trial also included: dollar spot severity, overall turfgrass quality and Poa annua establishment following the applications and creeping bentgrass safety.

Photo 1: One of the main challenges with using Velocity during the playing season for Poa control is the subsequent voids creating by killing grassy weeds.
Photo 1: One of the main challenges with using Velocity during the playing season for Poa control is the subsequent voids creating by killing grassy weeds.

Both studies were completed on fairways at Brookside Country Club, located in Pottstown, Pa., during the 2006 and 2007 seasons. All treatments were applied in a 1-gallon per 1,000-square-foot carrier volume. Velocity 17.6 WDG was applied twice in both studies at 30 grams active ingredient per acre (ai/A) approximately on a 14-day interval. In both trials, percent of plot area covered by healthy green Poa annua was rated visually on a 0 to 100 scale with 0 indicating no green, live Poa annua and 100 equalling entire plot area covered by Poa annua that was completely green and healthy. Percent bareground was rated on a 0 to 100 scale with 0 equaling no bareground and 100 indicating entire plot bareground with visible soil. 

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