Inroads to selectivity: Stacked cultivation in snap bean and beet

Mechanical cultivation can utilize more than one type of weed control implement in the same pass. Implements may even be synergistically “stacked” to maximize efficacy. However, in previous trials, stacked setups caused unacceptable damage to crops. In this study, several changes to previously used cultivation setups were made, including adding global positioning system guidance, using sweeps rather than torsion weeders, and spacing the implements farther from the crop. In test crops of snap beans and beets, stacked three-tool combinations resulted in greater weed-control efficacy with no significant decrease in the survival of well-established crops – thereby providing improved selectivity. Within one-, two-, or three-tool categories, there were few differences, except that the harrow-type implements were often less aggressive than the other tools. Combining all our trials, the crop-to-weed height ratio appeared to be a main driver of intrarow cultivation success, but stacking still provided a benefit. Specifically, to achieve successful cultivation with 80% weed control and 5% or less crop mortality, we modeled that one, two, and three tool combinations required crop-to-weed height ratios of at least 6.2, 5.6, and 3.6, respectively. Based on these trials, farmers may improve their cultivation selectivity by creating conditions in which their crops are as large as possible relative to weeds and by using precisely guided, stacked cultivation implements adjusted to minimize contact with crops.