Weed escapes and delayed weed emergence in glyphosate-resistant soybean

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.