CONTROL OF HERBICIDE-RESISTANT VOLUNTEER CORN IN HERBICIDE-RESISTANT SOYBEAN

Volunteer corn is a problem weed in soybean fields because it reduces yield and seed quality, and potentially harbors insects, pests, and diseases. Several pre-packaged herbicides have been registered in soybean in recent years, but response of volunteer corn to these herbicides has not yet been documented. Therefore, the first objective of this study was to evaluate the response of glufosinate-, glyphosate-, and imidazolinone-resistant volunteer corn to 20 pre-emergence (PRE) and 17 post-emergence (POST) soybean herbicides. The results indicated that PRE soybean herbicides partially controlled (\u3c 80%) volunteer corn except clomazone, while acetyl CoA carboxylase (ACCase) inhibiting herbicides provided ≥ 85% control. Germination and emergence are critical stages in weed seed establishment and persistence. Scientific literature is not available about the factors affecting germination and emergence of volunteer corn. The second objective was to determine the effects of different environmental and agronomic factors on the germination and emergence of glyphosate-resistant hybrid and volunteer corn. The results indicated that response of hybrid and volunteer corn to majority of the variables tested was similar, suggesting that volunteer corn can germinate and emerge in a wide range of climatic conditions. Majority of growers control volunteer corn when it is visible above the soybean canopy, but this can results in early season competition with soybean. The third objective was to evaluate the impact of different densities of glyphosate-resistant volunteer corn at different control timings, and late season volunteer corn emergence on soybean yields. Late season volunteer corn emergence had no significant effect on soybean yield. Yield did not decrease with all volunteer corn densities, except with the highest density (10,000 plants and 500 clumps ha-1) at all control timings. Soybean growers are looking for alternative herbicides, such as glufosinate, for management of glyphosate-resistant weeds, including volunteer corn. The fourth objective was to evaluate different herbicide programs for control of glyphosate-resistant volunteer corn in glufosinate-resistant soybean. The results suggested that glufosinate applied at different rates in a single or sequential application provided ≥ 85% control of volunteer corn along with other weeds. These results will provide useful information to soybean growers for management of volunteer corn. Adviser: Amit J. Jhal