Mixture interactions of iptriazopyrid with common auxin herbicides used in rice production

Abstract Nissan Chemical Corporation and Gowan ® USA are currently developing iptriazopyrid, a novel 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide for weed control in rice. Field experiments were conducted at the H. Rouse Caffey Rice Research Station near Crowley, LA to evaluate iptriazopyrid mixed with common auxin herbicides used in Louisiana rice production. Iptriazopyrid was applied at a reduced rate of the proposed 1x label rate to determine possible compatibility issues. The study was organized as a randomized complete block with a two-factor factorial arrangement of treatments, and treatments were applied at 94 L ha -1 postflood. Factor A consisted of either no iptriazopyrid or iptriazopyrid applied at 50 g ai ha -1 whereas factor B included each auxin herbicide. Across all evaluation intervals, barnyardgrass was controlled 68 to 80% whereas broadleaf signalgrass was controlled 27 to 31% when iptriazopyrid was applied alone. Iptriazopyrid alone controlled barnyardgrass 80% 35 days after treatment, compared to 29 and 43% when iptriazopyrid was mixed with triclopyr or 2,4-D, respectively. Mixtures of iptriazopyrid with triclopyr and 2,4-D resulted in antagonism for barnyardgrass, while only the iptriazopyrid and 2,4-D mixture was antagonistic for broadleaf signalgrass control. The mixture of iptriazopyrid with quinclorac indicated a neutral interaction for both grasses while an antagonistic interaction was observed for alligatorweed control. Iptriazopyrid mixed with florpyrauxifen resulted in a neutral interaction across all weed species evaluated and proved to be the most compatible mixing partner among the auxin herbicides within these studies. The results of these studies indicate that iptriazopyrid should not be mixed with triclopyr or 2,4-D when targeting barnyardgrass. To prevent antagonistic interactions split applications or alternative mixture partners should be considered. Supplemental research is needed to determine if antagonism is rate dependent and if increasing the rate of iptriazopyrid to the 1x labeled rate will overcome the antagonism.