Interactions of herbicides and other agrochemicals in plants: Interactions in mixtures with other herbicides and with safeners, fungicides, insecticides, and nematicides

Application of two or more herbicides, simultaneously or sequentially, within one cropping season is a very common approach for weed management. This review will consider simultaneous exposure of plants to multiple herbicides, as well as other agrichemicals, to be the same phenomenon whether the multiple exposure is the intentional result of the application of a mixture of agrichemicals or from sequential application of the chemicals. Simultaneous use of two or more herbicides is being further promoted by increased marketing of prepackaged herbicide blends. Prepackaged herbicide mixtures often combine the convenience of prepackaging with a lower cost compared to the mixture components purchased separately. There are management, economic, and environmental advantages for avoiding reliance on a single herbicide for weed control in a crop. The concept that optimum weed management systems could employ multiple herbicides, rather than a single herbicide, was a fundamental advance in use of these chemicals. This, in turn, has led to the concept of “prescription weed control”, where the actual components and amounts in a herbicide mixture are specifically tailored to the unique environmental, weed population, and crop situation within a field. The simplest example of a herbicide mixture for prescription weed control is where a herbicide primarily effective against broad-leaf (dicotyledonous) weeds is combined with an herbicide primarily effective against grass (graminaceous) weeds. The widely used combination of a triazine herbicide (such as atrazine, 6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine) for broad-leaf weeds with an acetanilide herbicide (such as alachlor, 2-chloro-N-(2,6-diethylpheny!)-N-(methoxymethyl)acetamide) for grass weeds in corn (Zea mays L.) production is an example of such a combination.