Bahiagrass (Paspalum notatum) seedhead suppression following consecutive yearly applications of plant growth retardants

Field trials evaluated sequential applications of plant growth retardants (PGRs) to bahiagrass for a 3-yr period at two Florida locations: Newberry (north Florida) and Okeechobee (south Florida). Seven PGRs from various chemical families were used: glyphosate, fluazifop, sethoxydim, maleic hydrazide, trinexapac-ethyl, imazapic, and imazaquin. In 1991 and 1992, PGRs reduced turf color for 2 to 4 wk after treatment (WAT) at the Newberry location but remained above acceptable levels (> 5.0) and recovered by 6 WAT. In 1993, glyphosate, fluazifop, and maleic hydrazide reduced turf color below acceptable levels (< 5.0) 4 WAT, but turf color was acceptable by 6 WAT. Turf color was slightly reduced following single and sequential imazapic applications in Okeechobee; however, turf recovered by 8 WAT. Cumulative seedhead suppression at both locations increased during the 3 yr resulting in at least a 60% reduction in seedhead numbers. Seedhead production each year was 10 to 50% less at 12 WAT in treated plots than in the previous year. Single applications of imazapic and imazapic + imazaquin provided 85 to 100% seedhead suppression for 12 WAT and 100% suppression for up to 16 wk following sequential applications made 8 wk after the initial application (WAI). Single applications of glyphosate, fluazifop, and maleic hydrazide provided ≥ 70% seedhead suppression for 4 to 8 WAT. Sequential applications of fluazifop made 8 WAI provided > 70% control of seedheads through 8 to 16 WAI for 3 yr.