Submitted to: Crop Protection Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2006
Publication Date: 3/1/2007
Publication URL: ars.usda.gov/SP2UserFiles/Place/36450000/Products-Reprints/2007/1394.pdf
Citation: Scursoni, J.A., Forcella, F., Gunsolus, J. 2007. Weed escapes and delayed weed emergence in glyphosate-resistant soybean. Crop Protection Journal. 26:212-218. Interpretive Summary: There are several explanations for the occasional failure to achieve excellent weed control in Roundup-Ready cropping systems. We explored one of these explanations in detail during two years in soybean crops at four Minnesota locations. Both one-pass glyphosate and two-pass glyphosate systems were examined (glyphosate is the active ingredient of Roundup-type herbicides). Weed seedling emergence patterns of different weeds were studied to identify the influence of delayed emergence on weed escapes. Ten species were recorded as weed escapes with common lambsquarters and eastern black nightshade present at all locations. Late weed emergence was the main reason for weed escapes with the one-pass glyphosate treatment. Lambsquarters showed a long period of emergence, thereby allowing its late-emerging seedlings to avoid contact with the herbicide. All nightshade seedlings emerged late and, therefore, its entire seedling population escaped glyphosate treatment. The amount of seeds produced by these escaped weeds was related closely to their groundcover at the end of the growing season, which allows estimation of the extent of future problems presented by these weeds. This information can be used by agronomists, crop advisors, and the agrichemical industry to better plan weed control strategies for late-emerging weed species in Roundup-Ready cropping systems.
Technical Abstract: During 2001 and 2002, field experiments were conducted in soybean crops at four Minnesota locations with the aim of studying the effects of different glyphosate treatments (one-pass glyphosate, two-pass glyphosate) on weed control and weed community composition by focusing on the identity and abundance of weeds that escaped from different treatments. In addition, seedling emergence patterns of different weeds were studied to identify the influence of delayed emergence on weed escapes. Overall, 10 species were recorded as weed escapes and Chenopodium album L. and Solanum ptycanthum Dunal were present at all locations. Late weed emergence was the main reason of weed escapes with one-pass glyphosate. C. album showed a long period of emergence, thereby allowing the late-emerging cohorts to avoid contact with the herbicide. S. ptycanthum emerged late and therefore its entire seedling population escaped glyphosate treatment. These weeds showed a robust relation fecundity (seeds/m2) and plant ground cover. C. album ground cover of 0.1% may produce around 500 seeds/m2.