USING ESTIMATES OF WEED PRESSURE TO ESTABLISH CROP YIELD LOSS EQUATIONS

Herbicide efficacy trials in field com, sweet com, and soybean were conducted at three locations in Wisconsin over a 6-yr period. Percent weed pressure (WP) was determined by visually estimating the contribution of all weed species present to the total crop and weed volume in each plot. Crop yields in each plot were measured. Percent crop yield reduction (YLDRED) was calculated by comparing mean yields of individual treatments with those of the highest yielding treatment in each trial. Linear regression analyses of YLDRED and WP data from 1640 field com and 138 sweet com treatments were significant. Nonlinear regression analysis of YLDRED and WP data from all 1374 soybean treatments was significant; however, a linear regression of those 11 54 soybean treatments with WP ratings of 30 or less produced a more easily interpreted regression equation.