As cotton is naturally sensitive to a range of herbicides used for the control of broadleaf weeds, post-emergence suppression of such weeds is limited to relatively inefficient lay-by herbicides and mechanical means including interrow cultivation and hand chipping. Cotton cannot be treated with over-the-top applications of effective broadleaf herbicides such as Roundup and 2,4-D, and is, intact, often adversely affected by the drift of 2,4-D sprayed on grain crops in nearby fields. The introduction of genes for herbicide resistance by genetic engineering of cotton may not only provide resistance to this drift damage, but could also make possible the direct application of previously toxic herbicides to the cotton crop, thereby increasing the options for weed control.