Witchweed Control by Herbicides Translocated Through Host Plants

Abstract

Dicamba (3,6-dichloro-o-anisic acid) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) applied in lanolin pastes to leaves or roots of host plants growing in soil were translocated acropetally and affected witchweed (Striga lutea Lour.) plants parasitizing roots of host plants. Emerged witchweed plants exhibited characteristic epinastic responses while emergence of other witchweed plants was delayed. Broadcast foliar treatments of dicamba and 2,3,6-TBA to corn (Zea mays L.) applied before witchweed emergence generally reduced the intensity of the infestation and delayed emergence. However, injury to corn, expressed as failure of kernel development and grain yield decreases, sometimes occurred. Injury was greater when herbicide application was delayed until corn was in the early tassel stage. Dicamba was more effective than 2,3,6-TBA for witchweed control. However, no treatment gave season-long control of witchweed. Yearly variations in corn injury precluded a selection of optimum treatment dates and rates for control of witchweed by this technique.