Herbicide Antagonism at the Whole Plant Level

Antagonistic interactions between herbicides or between herbicides and nonherbicides are common and prevent the use of certain mixtures. Although antagonism is detrimental when it reduces weed control, the degree of antagonism is critical to determine whether a mixture is agronomically useful. If antagonsim is not severe, herbicides with different weed spectrums can be used together to complete the weed spectrum. Antagonism can be beneficial when it increases crop safety. In cases where antagonism significantly reduces control, key factors must be identified and managed to decrease antagonism and increase efficacy. These factors, which include the herbicide rate(s), mode of action, plant species, formulation, adjuvants, timing, stage of growth, and environment, often are complex and poorly understood at the whole plant level. The growing dependence on herbicide mixtures has increased the practical importance of understanding herbicide antagonism.