Short communicationImpact of glyphosate-resistant volunteer corn (Zea mays L.) density, control timing, and late-season emergence on yield of glyphosate-resistant soybean (Glycine max L.)

- To evaluate (1) the impact of glyphosate-resistant volunteer corn density on soybean yields, present as individual plants or clumps, and controlled at different soybean growth stages (V4, V6, or R2), and (2) late-season volunteer corn emergence on soybean yields.
- To maintain the desired number of isolated volunteer corn plants and clumps, individual seeds and/or corn ears were hand-planted in each plot based on their respective target densities.
- Late season emergence of volunteer corn planted at different densities had no effect on soybean yield at both sites during both years.
- When volunteer corn was left uncontrolled or controlled at the R2 soybean growth stage, soybean yield was the lowest under the highest number of isolated volunteer corn plants (10,000 plants ha−1) plus clump density (500 clumps ha−1).

Glyphosate-resistant (GR) volunteer corn is a troublesome weed in soybean fields in a corn-soybean rotation as well as in corn fields in a continuous corn production system. The objectives of this study were to evaluate the impact of (1) different densities of GR volunteer corn on soybean yields, present as individual plants or clumps, controlled at fourth trifoliate (V4), sixth trifoliate (V6), or full flowering (R2) soybean growth stages, and (2) late-season volunteer corn emergence on soybean yields, after being controlled at different soybean growth stages. Field experiments were conducted in 2013 and 2014 under irrigated conditions in Clay County, Nebraska, and under rain-fed conditions in Lancaster County, Nebraska, USA. To maintain the desired number of isolated volunteer corn plants (1250, 2500, 5000, and 10,000 plants ha−1) and clumps (63, 125, 250, and 500 clumps ha−1), individual seeds and/or corn ears were hand-planted in each plot based on their respective target densities. Volunteer corn was controlled with applications of clethodim at V4, V6, or R2 soybean growth stages. Late-season volunteer corn emergence had no effect on soybean yield with volunteer corn densities and control timings at both locations in 2013 and 2014. During the first year of study at Clay County, volunteer corn densities and control timings had no effect on soybean yield. When volunteer corn was left uncontrolled or controlled at the R2 soybean growth stage, yield was the lowest at highest isolated volunteer corn plants (10,000 plants ha−1) plus clump density (500 clumps ha−1) during the second year of study in Clay County (≤5068 kg ha−1) and during both years of study in Lancaster County (≤1968 kg ha−1).