Influence of Various Plant Populations On Weed Removal Timing in Glyphosate-Resistant Soybean.

Reduced plant population in glyphosate-resistant soybean [Glycine max (L) Merr.] may influence the critical time of herbicide application.  Field studies were conducted in 2007 and 2008 at two locations in Kentucky to determine the effect of four weed control programs on soybean seed yield, seed quality, crop canopy, and weed pressure when planted at three densities - 185,000, 309,000, and 432,000 plants ha^-1.  Plots were treated with glyphosate at either 3 weeks after planting (WAP), 5 WAP, 7 WAP, 3 & 7 WAP.   No differences in seed yield were discovered between plant densities in two of four site-years.  254,500 plants ha^-1 was sufficient for maximum yields in all site-years and was also sufficient to achieve maximum canopy amongst those populations tested in the study.  Sequential applications at 3 and 7 WAP provided the highest seed yield, while the 5 WAP and 7 WAP application timings generally allowed for the highest yield and canopy closure, along with the highest visual estimate of weeds controlled.  Soybean plant density in 38-cm rows did not influence the critical period for weed control.