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.

Field studies were conducted in 1996 and 1997 to determine postemergence control of purple (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) by single and sequential applications of bentazon, halosulfuron, and sulfentrazone; sequential applications of MSMA; and single applications of imazaquin and imazaquin plus MSMA. Sequential applications of halosulfuron at 70 g ai/ha controlled purple nutsedge more effectively at 10 wk after initial application (WAI) than all other herbicides. Single applications of imazaquin (0.56 kg ai/ha) or imazaquin plus monosodium salt of methylarsonic acid (MSMA, 2.24 kg ai/ha) controlled purple nutsedge adequately 6 WAI (78 and 90%, respectively) but not 18 WAI. Single applications of either halosulfuron (70 g/ha) or imazaquin plus MSMA or sequential applications of either bentazon (1.12 kg ai/ha), MSMA (2.8 kg/ha), or halosulfuron controlled yellow nutsedge greater than 80% by the end of the season in 1996 when nutsedge was in bermudagrass (Cynodon dactylon L.). However, in absence of bermudagrass in 1997, only sulfentrazone or the halosulfuron sequential treatments controlled yellow nutsedge 13 WAI. In 1996, single and sequential applications of halosulfuron reduced viability of purple nutsedge tubers to 33 and 30%, respectively, compared to 84% in the nontreated control. However, herbicide treatments did not reduce tuber viability in 1997. Sulfentrazone (0.28 kg ai/ha) plus MSMA (2.24 kg/ha) and sequential MSMA applications reduced viability of yellow nutsedge tubers to 6 and 31%, respectively, in 1997.