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. 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.

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. 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. 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 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. The spread of herbicide-resistant weeds across agrophytocenoses poses a threat of decrease in the effectiveness of use of herbicides in agricultural fields. Many countries are now facing the problem of increase in resistant biotypes of weeds. This study concludes that the co-application of atrazine with HPPD-inhibitors applied postemergence reduced the risk of herbicide failure and resulted in greater and more consistent control of MHR waterhemp. Averaged across herbicide treatments and sites, the addition of atrazine reduced the standard error of MHR waterhemp control by 13% to 100%. Averaged across field sites, the addition of atrazine to isoxaflutole, mesotrione, topramezone, or tembotrione improved MHR waterhemp control 15%, 11%, 7%, and 7%, respectively at 4 weeks after application (WAA). Corn injury (≤ 10%) was observed at specific sites where the application of tembotrione, isoxaflutole and isoxaflutole + atrazine resulted in characteristic white bleaching of corn foliage however, yield was not affected. Five HPPD-inhibiting herbicides were applied postemergence with and without atrazine to 10-cm-tall waterhemp. Five field trials were conducted over a two-year period (2018, 2019) in Ontario, Canada.

The objective of this research was to determine if the addition of atrazine to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides applied postemergence improves their consistency of MHR waterhemp (including Group 5 resistance) in corn. The complementary activity of the co-application of hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides with atrazine has been well documented. The evolution of multiple-herbicide-resistant (MHR) waterhemp (resistant to Groups 2, 5, 9, and 14) in Ontario, Canada is challenging for growers.

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