A Method of Evaluating Herbicide Combinations and Determining Herbicide Synergism

Abstract

Several methods of evaluating plant responses to combinations of herbicides are discussed. They include: a direct-plot of percent response vs toxic units; determining ID50(dosage that causes a 50% reduction in growth of the treated plant) for each herbicide and for each combination; percent response vs log-dosage; double reciprocal procedures; probit analysis, and calculation of expected values. A simplified version of the isobole method of Tammes (23) is presented as a method which can be readily applied by weed scientists to determine the validity of data on plant responses to herbicide combinations. Definitions are proposed which classify plant responses to herbicide interactions as additive, synergistic, antagonistic, or enhancement. Four points are listed that will improve the quality of data obtained from experiments on combinations.