Direct versus Indirect Herbicide Effects: The Example of Preplant Incorporated Halosulfuron

The potential indirect effects of soil applied herbicides have not been adequately explored. The objective of this study was to explore the potential and relative importance of the indirect effects of halosulfuron applied preplant incorporated (PPI) on several weed species common in white bean fields in Ontario. Halosulfuron applied PPI at 35 g ai ha-1 delayed common lambsquarters and wild mustard emergence and reduced their densities over 70%. It did not delay green foxtail emergence, but the density was decreased over 30%. Indirect herbicidal effects such as delayed emergence timing may be important for weed management in non-competitive crops such as white bean. Based on these results, the indirect effects of soil applied herbicides are real and are potentially important for providing additional prevention of yield loss in field crops. This may be particularly important for relatively non-competitive crops such as white bean and for reducing weed seed return to the seedbank.