Turf Weeds at Virginia Tech

Turf Weeds was developed to provide weed management information and newsearch reports to turfgrass managers. This site contains information on weed identification, chemical and cultural management of weeds, and current topics relevant to weed management in lawns and professional turf. Turf Weeds was created by Dr. Shawn Askew, Assistant Professor of Turfgrass Weed Science at Virginia Polytechnic Institute & State University.

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DEGREE DAY FOR PREDICTING ANNUAL BLUEGRASS SEEDHEAD EMERGENCE

Description:
Author:	S.D. Askew, D.R. Spak, W.L. Barker, J.B. Willis, and D.B. Ricker
Author Org:	Virginia Tech
Date:	01/05/2005
Presenter:	S. D. Askew
Conference:	Northeastern Weed Science Society
Location:	Washington, DC
File Formats:
Abstract:	Determining proper timing of plant growth regulators (PGR’s) for annual bluegrass (Poa annua) is difficult. The most common plant growth regulators (PGR’s) used to suppress annual bluegrass seedheads on golf putting greens include ethephon (Proxy) and mefluidide (Embark). Mefluidide, although effective for AB seedhead suppression, consistently discolors desirable creeping bentgrass. Recent research has indicated that mixtures of ethephon and trinexapac ethyl (Primo) (E+T) can suppress AB seedheads and improve putting green aesthetics in a single treatment. Although potentially effective for AB seedhead suppression, E+T can be inconsistent and ineffective when applied too early or too late. A mixed creeping bentgrass and AB putting green in Blacksburg, VA and Fairway in Lancaster, PA was treated with E+T at different times and both soil temperature and Forsythia (Forsythia x intermedia) bloom phenology were evaluated. Our objective was to determine biological indicators of AB bloom initiation and optimal timing for PGR treatment and to compare on-site soil temperature data to local weather station data for GDD estimation. AB first bloomed upon sustained soil temperatures of greater than 13 C on April 15 in VA and April 20 in PN. Soil and air DD50 values varied by only two days for predicting annual bluegrass seedhead emergence. First annual bluegrass bloom occurred at both locations when GDD50 reached a cumulative value between 61 and 90. At this time, Forsythia blooms on north-facing slopes first began to drop and Forsythia blooms on south-facing slopes had dropped 50%. Treatments applied within two weeks of seedhead production were most effective for AB seedhead suppression. Preliminary estimates are that E+T should be applied at a cumulative GDD50 of 50 or when Forsythia is in full bloom but bloom drop has not occurred.

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