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.
Annual bluegrass control was reduced following 7 yr of continuous fall application of dinitroaniline (DNA) herbicides. Annual bluegrass control was < 40% on two fairways in year eight following prodiamine applied at 1.1 kg ai ha−1. In dose–response studies conducted in growth chambers, this annual bluegrass population exhibited 105-fold resistance in shoot growth to prodiamine compared with a known susceptible population. A 6.4-fold resistance to prodiamine was found when comparing annual bluegrass root growth to the known susceptible biotype. Spring-applied oxadiazon did not affect shoot or root growth between annual bluegrass biotypes. Equivalent levels of control were attained with pronamide. The presence of DNA-resistant annual bluegrass, in addition to previously confirmed triazine-resistant biotypes on North Carolina golf courses, indicates a need for resistance management strategies to be integrated into golf turf management practices.
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