Preharvest Herbicide Treatments Affect Black Bean Desiccation, Yield, and Canned Bean Color

To facilitate direct harvest, preharvest herbicide applications are used to desiccate weeds and to accelerate and promote uniform dry bean (Phaseolus vulgaris L.) maturation. Field trials were conducted near Richville, MI, in 2013 and 2014 to evaluate the effects of preharvest herbicide treatments on desiccation, yield, and canned black bean quality and color. Three black bean cultivars, Zorro, Eclipse, and Zenith, were planted on two different dates in each of 2 yr. Three preharvest herbicide treatments, paraquat, glyphosate, and saflufenacil, were applied at a standard (pods = 80% yellow) and an early (pods = 50% yellow) application timing. A nontreated control was established for each cultivar. Differences in black bean desiccation were greatest 3 d after treatment (DAT), with paraquat and saflufenacil showing the quickest desiccation at the early application timing. By 7 DAT, desiccation for most preharvest treatments was >95%. Saflufenacil applied at the early timing reduced yield by as much as 55% compared with the nontreated control. Yield was generally not affected when preharvest herbicide treatments were applied at the standard application timing. Black bean cultivar influenced canned bean color retention (Zenith > Zorro > Eclipse). Preharvest herbicide treatments reduced color retention when applied at the early application timing; glyphosate reduced color retention by as much as 24%. Because of variability in bean maturation rate within a field, preharvest herbicide treatments need to be applied as close to physiological maturity as possible to minimize yield losses and maintain color retention of canned black bean.