Preemergence Herbicides Effect on Growth and Yield of Early-Planted Mississippi Soybean

Abstract

The objective of this research was to evaluate the impact of full and reduced rates of PRE herbicides, applied alone or in combination, on growth and yield of selected April-planted soybean varieties in the lower Mississippi River alluvial flood plain. Field studies were conducted in 2001 and 2002 at Stoneville, MS, to evaluate the effects of preemergence (PRE) herbicides on growth and yield of early-planted soybean. Main plot factor was PRE grass herbicide. Sub-plot factor was PRE broadleaf herbicide. Sub-sub-plot factor was soybean variety. Soybean injury 8 weeks after treatment (WAT) in 2001 under cool and wet growing conditions ranged from 11 to 31% when PRE broadleaf herbicides were applied alone. Pendimethalin alone caused 31% soybean injury 8 WAT. Soybean injury with PRE combinations of pendimethalin at 1120 g ai/ha and broadleaf herbicides ranged from 29 to 49%. Soybean injury with flumioxazin alone was 26 to 31% compared to 38 to 49% with mixtures of S-metolachlor and flumioxazin. Conditions after planting were warmer and drier in 2002 than 2001, but all herbicide treatments still resulted in noticeable soybean injury. Soybean injury from PRE broadleaf herbicides tended to be less with the sulfonylurea-tolerant soybean (STS) variety, especially in 2001. Averaged across PRE grass herbicides, soybean yield was reduced both years by metribuzin at 694 g ai/ha and sulfentrazone + chlorimuron at 231 + 38 g ai/ha. Averaged across PRE broadleaf herbicides, pendimethalin reduced soybean yield 4% in 2001 and S-metolachlor reduced soybean yield 3% in 2002.