Abstract

Preemergence herbicides are used to control weeds of bermudagrass turf, but may reduce establishment of subsequently overseeded perennial ryegrass. This research demonstrated the use of nonlinear regression to predict preemergence herbicide effects on subsequently overseeded perennial ryegrass. Preemergence herbicides dithiopyr, pendimethalin, and prodiamine were applied at single rates every week between 10 and 0 weeks before perennial ryegrass overseeding. Reduction in perennial ryegrass stand and cover were nonlinearly regressed on herbicide application date, in days before overseeding, using an exponential decay function. Reduction in perennial ryegrass stand and cover were moderately to highly determined, r2 = 0.76 to r2 = 0.97, and herbicide half-life in reducing stand and cover varied by herbicide and application rate. For dithiopyr the half-life was between 8 and 16 days, for pendimethalin, the half-life was between 10 and 15 days, and for prodiamine the half-life was between 30 and 63 days. The exponential decay function also predicted necessary delay to overseeding, for a given reduction of stand or cover. While the specific prediction values may only be applicable to the southern region of Florida, nonlinear regression is useful in predicting preemergence herbicide effects, over a range of dates, on subsequently overseeded perennial ryegrass, based on an exponential decay function.