Nissan Chemical Corporation and Gowan USA are currently developing iptriazopyrid, a novel herbicide that inhibits 4-hydroxyphenylpyruvate dioxygenase (HPPD), for weed control in rice. Field experiments were conducted near Crowley, Louisiana, to evaluate iptriazopyrid mixed with common auxin herbicides used in Louisiana rice production. Iptriazopyrid was applied at a reduced rate of the proposed 1 × 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 post-flood. 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 by 68% to 80%, whereas broadleaf signalgrass was controlled by 27% to 31% when iptriazopyrid was applied alone. Iptriazopyrid alone controlled barnyardgrass by 80% 35 d after treatment, compared with 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 whether antagonism is rate dependent and whether increasing the rate of iptriazopyrid to the 1 × labeled rate will overcome the antagonism.

Iptriazopyrid is a novel herbicide that inhibits 4-hydroxyphenylpyruvate dioxygenase. When it receives authorization for use in rice production, iptriazopyrid will be the first azole carboxamide herbicide to receive registration for use in the United States. Because herbicides are commonly mixed to broaden the weed control spectrum and efficacy, herbicide interactions with iptriazopyrid must be evaluated. Field experiments were conducted near Colt, Arkansas, in 2024 and 2025, to evaluate interactions between iptriazopyrid and either synthetic auxins or residual herbicides labeled for use in rice fields. The experiments were designed as a two-factor, randomized complete block design, with the presence of iptriazopyrid at 50 g ai ha−1 as the first factor and the presence of labeled synthetic auxins or residual herbicides as the second factor. Applications targeted barnyardgrass at the 3- to 4-leaf stage, and Colby’s method was utilized to determine herbicide interactions. Only 2,4-D demonstrated antagonism to iptriazopyrid throughout the experiments. When applied alone, iptriazopyrid provided 75%, 83%, and 79% barnyardgrass control at 1, 2, and 4 wk after treatment (WAT), respectively, compared with 12%, 18%, and 8% control when it was mixed with 2,4-D. The iptriazopyrid + triclopyr combination was antagonistic for barnyardgrass control at 1 and 2 WAT, with 61% and 73% control, respectively; however, the relationship was no longer significant at 4 WAT. Barnyardgrass density supported an antagonistic interaction between 2,4-D and iptriazopyrid because combinations of the two led to higher densities than iptriazopyrid applied alone. No residual herbicide antagonized iptriazopyrid for barnyardgrass control; nor did barnyardgrass densities differ when iptriazopyrid was applied alone. Overall, these findings show that iptriazopyrid offers reasonable flexibility when mixed with some, but not all, synthetic auxins labeled for rice, and that there is no reduction in barnyardgrass efficacy when mixed with residual herbicides.