USE OF PRODIAMINE AS A PREEMERGENCE HERBICIDE TO CONTROL ANNUAL BLUEGRASS IN KENTUCKY BLUEGRASS

Annual bluegrass (Poa annua L.) is an intractable weed problem on golf courses. Much has been written about annual bluegrass, but there is l ittle documentation of regional germination period(s) and the proper t iming of preemergence herbicides targeted for the control of the annua l biotype (P. annua ssp. annua [L.] Timm. = AB), The objectives of thi s field study were to determine the optimum prodiamine rate and timing for effective AB control. The turf was a mature stand of 'Kenblue' Ke ntucky bluegrass (Poa pratensis L.) maintained under conditions simila r to those imposed for golf course roughs. Three rates of prodiamine ( 0.36, 0.73, and 1.1 kg.ha(-1)) were applied on three dates in 1995 (11 Aug., 14 Sept., and 13 Oct.) and 1996 (29 Aug., 16 and 30 Sept.), All rates applied 11 Aug. or 14 Sept. 1995, and 29 Aug, or 16 Sept. 1996 effectively controlled AB. None of the rates applied 13 Oct. 1995 redu ced AB cover, and the 0.36 kg.ha(-1) rate applied 30 Sept. 1996 provid ed relatively poor AB control. Data and observations indicated that th e major germination period for AB was between late September and early December. Effective AB control was achieved whenever prodiamine, rega rdless of rate, was applied between mid-August and mid-September. Thes e prodiamine rates and this application window may be effective only i n relatively high cut turf (i,e., >5.0 cm) in the mid-Atlantic region, Chemical names used: O,O-bis(1-methylethyl) S-{2-[(phenylsulfonyl)ami no]ethyl) phosphorodithioate (bensulide); 2,4-dimitro-6-(trifluorometh yl)-m-phenylenediamine (prodiamine).