ABSTRACT
Preemergence (PRE) herbicides, applied in late winter, effectively control the emergence of smooth crabgrass (Digitaria ischaemum L.) in bermudagrass (Cynodon sp.) turf. However, reduced rate programs for PRE herbicides are becoming of greater interest, due to both environmental and cost benefits. Research was conducted over four years, on common bermudagrass (Cynodon dactylon) grown in two locations, to evaluate the efficacy of four reduced rate programs with five PRE herbicides. All reduced rate programs began with a full rate application in year one, followed by varying rate reductions and application frequencies in the latter three years. Select reduced rate programs with prodiamine and pendimethalin provided >80% control of smooth crabgrass at both locations while reduced rate programs with dithiopyr were effective at only one location. Weed control was achieved with all reduced rate programs except the one where a PRE herbicide was not applied each year. Results suggested that success of reduced rate programs may be dependent on site conditions, particularly soil texture and rainfall. The 20–40% reduction in herbicide use with successful reduced rate programs may significantly reduce the cost of applying PRE herbicides, even though the potential for reduced environmental impact remains uncertain. Based on the success of reduced rate programs, neither augmentation of smooth crabgrass control with cost effective postemergence (POST) applications nor reversion back to annual full rate applications of PRE herbicides would seem necessary.
