WEED SCIENCE Glyphosate-Resistant Cotton Interference in Glyphosate-Resistant Soybean

A negative aspect of glyphosate-based man-agement systems is the potential for volunteer glyphosate-resistant (GR) crop plants to impact subsequent crops. Two independent studies were conducted to determine the effect of differing density (full-season competition) and differing duration of interference (constant density) of GR cotton (Gossypium hirsutum L.) on GR soybean (Glycine max (L.) Merr.) growth and yield. Cot-ton density and duration of interference effects were not observed on soybean height at harvest. Season-long competition with a cotton density of 1 plant per row m would be expected to reduce soybean yield 6%. A cotton density of 5.25 plants per row m would have to interfere with soybean for at least 6 wk following emergence before a yield reduction would be expected. Even then, yield reduction would be significantly lower than 1%. The cotton densities and duration of inter-ference periods evaluated did have a significant impact on soybean yield. However, impact does not appear to be as significant as other common problematic grass or broadleaf weeds