Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/3/2006
Publication Date: 7/1/2006
Citation: Scursoni, J., Forcella, F., Gunsolus, J.L., Owen, M.D., Oliver, R., Smeda, R.J., Vidrine, P.R. 2006. Weed diversity and soybean yield with glyphosate management along a north-south transect in the United States. Weed Science. 54:713-719. Interpretive Summary: Some weeds escape control by glyphosate (for example, "Roundup") in glyphosate-tolerant (GT) crops. These species likely will become bigger problems with repeated use of GT crops. Identifying these weeds and their mechanisms of escape might allow us to develop more effective management strategies. We studied the number and abundance of escaped weeds as influenced by glyphosate application compared to conventional herbicide-based weed management systems in GT soybean along a north-south transect from Minnesota to Louisiana. Low-intensity use of glyphosate often allowed a select group of weed species to escape control, but at relatively low densities. The same weeds escaped from low- and high-intensity glyphosate treatment, but their frequency of escape was higher with less intensive use. Otherwise, it has little effect on weed biodiversity compared to conventional management systems, primarily because many species escape glyphosate through delayed seedling emergence. This is basic information regarding the environmental consequences of using GT crops, and it will be of interest to other scientists, the commercial seed industry and, perhaps, action agencies such as EPA and NRCS.
Technical Abstract: There are many concerns today about the effects of glyphosate tolerant crops. These include (i) weed escapes from glyphosate and (ii) loss of biodiversity related to the extended use of herbicide resistant crops. Some weeds do escape this effective herbicide, and represent species that likely will become bigger problems in the future. Identifying these weeds and their mechanisms of escape allows development of more effective management strategies. We studied the effects of glyphosate application compared to conventional weed management in transgenic soybean in terms of biodiversity and weed community composition in a north-south transect of sites spanning a distance of 1600 km from Minnesota to Louisiana. We show that low-intensity use of glyphosate maintained higher biodiversity than high intensity use of glyphosate and equivalent or higher diversity than conventional herbicide-based weed systems. The same weeds species escape from low- and high-intensity glyphosate treatment. However, their frequency of escape was higher with less intensive use. These results suggest that judicious use of glyphosate will not have profound effects on biodiversity of agroecosystems, primarily because many weed species escape glyphosate through delayed seedling emergence.