Effects of interaction and effectiveness of weed control when using tank mixtures of herbicides in maize crops

Many countries are now facing the problem of increase in resistant biotypes of weeds. The spread of herbicide-resistant weeds across agrophytocenoses poses a threat of decrease in the effectiveness of use of herbicides in agricultural fields. In order to develop anti-resistant compositions of herbicides for protection of maize (Zea mays L.) crops, we studied effects of interaction and efficiency of weed control in greenhouse and field experiments. We studied the possibility of combined use of 4-hydroxyphenyl pyruvate dioxygenase-inhibiting herbicide tolpyralate and inhibitor of transport of electrons in photosystem 2 of chloroplasts – terbuthylazine – and acetolactate synthase-inhibiting rimsulfuron. In greenhouse experiments on model objects, we found that interaction in the mixtures of tolpyralate with rimsulfuron was antagonistic, but the antagonism may be overcome by increasing the rate of applied rimsulfuron. At joint use of tolpyralate and terbuthylazine, a synergistic increase in phytotoxic effect was observed, caused by increase in the effectiveness of the blocking electron-transport chain and increase in intensity of formation of reactive oxygen species. According to the results of the field experiments, we drew the conclusion that the efficacy of using the mixture of tolpyralate and rimsulfuron depends on the species composition of weeds. In the presence of rimsulfuron-resistant weeds, interaction with tolpyralate becomes antagonistic even in the conditions of increased rate of application of rimsulfuron, and thus the effectiveness of the protection significantly decreases. At the same time, after applying tank mixture of tolpyralate with terbuthylazine, the synergistic character of the interaction was maintained toward a broad range of species of grass and dicotyledonous weeds, providing high efficiency of maize crop protection. The herbicide compositions that were analyzed and are presented in the article allow one to decrease the possibility of emergence of resistant biotypes of weeds, and also to effectively control the already existing resistant biotypes.