Weed control, environmental impact and profitability of reduced rates of imazethapyr in combination with dimethenamid in dry beans

Abstract

Field experiments were conducted from 2003 to 2005 in Ontario to determine if reduced rates of imazethapyr (< 75 g a.i. ha-1) tank-mixed with dimethenamid applied preemergence (PRE) can be used as a feasible weed management strategy for broad-spectrum weed control in white and kidney beans (Phaseolus vulgaris L.). There was no injury in white or kidney bean with the imazethapyr plus dimethenamid tank-mix treatments evaluated. The rate of imazethapyr required to provide adequate control of green foxtail [Setaria viridis (L.) P. Beauv.], lamb’s-quarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.), wild mustard (Sinapis arvensis L.), and redroot pigweed (Amaranthus retroflexus L.) tended to be reduced when tankmixed with dimethenamid at 1000 g ha-1. There was no adverse effect on the yield of white and kidney beans at the highest rate (75 g a.i. ha-1) of imazethapyr evaluated. Although both herbicides are considered reduced risk, the environmental impact of imazethapyr (75 g a.i. ha-1) was seven times less than that of dimethenamid (1000 g a.i. ha-1). The addition of reduced rates of imazethapyr to dimethenamid did not significantly increase environmental impact (EI) vs. dimethenamid alone. Profit margins were greater when dimethenamid was tank-mixed with imazethapyr than for applications of imazethapyr alone. Across all treatments, profit margins were maximized at an imazethapyr rate of 60 g a.i. ha-1 for white bean and an imazethapyr rate of between 60 and 75 g a.i. ha-1 for kidney bean. However, the profit-maximizing rates of imazethapyr tended to be higher for treatments without dimethenamid than for treatments where dimethenamid was tank-mixed with imazethapyr. Key words: Dimethenamid, environmental impact quotient (EIQ), imazethapyr, Montcalm, OAC Thunder, Phaseolus vulgaris L., profit margin