FIELD PASPALUM CONTROL IN TALL FESCUE. P.H. Dernoeden* and C.P. Ryan, University of Maryland, College Park, MD (89)


   Field or smooth paspalum (Paspalum laeve Michx.) is a growing weed problem in turfgrass sites in Maryland. Field paspalum is a warm-season perennial that has a bunch-type growth habit, but plants may develop short rhizomes. Leaves and sheaths are hairy and foliage typically appears grayish-green or yellow-green. Organic arsonates (DSMA and MSMA) have been used for decades to control Paspalum spp. in turf. The EPA has cancelled registration of DSMA and MSMA and sales of all products containing MSMA for use on golf courses, sod farms and highway right of ways will end December 31, 2012. Thus, new herbicides are needed to replace the arsonates for Paspalum spp. control. Three separate studies are reviewed. Fluazifop-P and sethoxydim were assessed in 2009 (unimproved site of Poa pratensis L. and Lolium perenne L.) and bispyrabac-sodium, fluazifop-P, sulfentrazone and sulfosulfuron were evaluated in 2010 ( tall fescue, Festuca arundinacea Schreb.) as postemergence treatments; mesotrione and siduron were assessed preemergence (PRE) in a spring seeded stand of tall fescue . The herbicides were applied in 50 GPA using a CO2 powered backpack sprayer equipped with an 8004E flat fan nozzle. Soil was a Keyport silt loam with a pH of 5.7 to 5.9 and 1.4 to 2.2% OM. Fluazifop-P was tank-mixed with 0.25% v/v non-ionic surfactant (NIS) in 2009 and 2010. Rates and dates of application are noted below. Plots were 5ft by 5ft and arranged in a randomized complete block with three (2009) or four replications (both 2010 sites). Field paspalum cover was assessed visually using a 0 to 100% scale where 0 = no paspalum and 100 = entire plot area covered by paspalum in 2009; in the 2010 post study the number of plants in each plot was counted. Turf quality was visually assessed using a 0 to 10 scale where 0 = entire plot area brown or dead and 10 = optimum green color and cover in the 2010 post study. Data were subjected to analysis of variance and significantly different means were separated by Fisher’s LSD test at P ≤ 0.05. On 10 June 2009, fluazifop-P (0.375 lb ai/A) and sethoxydim (0.47 lb ai/A) were applied to a dense stand of field paspalum (80% cover; FP). Data collected 54 days after treatment showed that fluazifop-P had provided complete control, while sethoxydim had provided 67% FP control. The mixed species turf was not injured, which was attributed to the dense FP canopy that likely intercepted most of the herbicide. In 2010, bispyrabac (0.033 and 0.066 lb ai/A), sulfentrazone (0.125 lb ai/A) and bispyribac + sulfentrazone (0.033 + 0.125 lb ai/A) were applied three times on 27 May, 11 June and 23 June; sulfosulfuron (0.023 lb ai/A) was applied twice on 27 May and 11 June; and fluazifop-P (0.375 lb ai/A) was applied once on 27 May 2010. Bispyrabac (0.033 lb/A) and fluazifop-P reduced tall fescue quality from 15 June to 5 Aug; bispyrabac (0.066 lb/A) reduced quality until 9 Sept.; sulfosulfuron almost completely eliminated the tall fescue; and sulfentrazone did not injure turf. Fluazifop-P and bispyrabac + sulfentrazone reduced FP populations (11 plants plot-1 = 84% control) compared to the control (68 plants plot-1). In the PRE study, mesotrione was applied once (0.50 lb ai/A) on 12 April or twice (0.125, 0.156, 0.187 and 0.25 lb ai/A) on 12 April and 12 May 2010 (0.25% v/v NIS on 12 May only); and siduron was applied once (12 lb ai/A) or twice (6.0 + 6.0 lb ai/A) on the aforementioned dates to mostly necrotic plant debris and some bare soil in a seedbed. Data were collected 9 Sept. 2010 and all treatments provided a statistically equivalent level of FP control. For mesotrione, control ranged 80 to 94% (2 to 11% FP cover) and for siduron control was 98% (1% FP cover). This may be the first report of PRE control of field paspalum in turf at spring seeding.