Selectivity Factors in the Response of Plants to 2,4-DB

Abstract

Foliar spray retention, absorption and translocation, and the dissipation of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were examined to determine their importance as selectivity factors in the response of two 2,4-DB-tolerant legumes, alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.), and two susceptible broadleaf weeds, redroot pigweed (Amaranthus retroflexus L.) and common cocklebur (Xanthium pensylvanicum Wallr.). The legumes were as effective as the broadleaf weeds in metabolizing (beta-oxidizing) 2,4-DB to 2,4-D. The relatively greater tolerance of the legumes than of the broadleaf weeds to 2,4-DB arose from a combination of poorer spray retention, less effective absorption and translocation, and a more rapid degradation of the 2,4-D arising from the beta-oxidation of 2,4-DB.