Tribenuron antagonized diclofop control of wild oat in greenhouse studies. Wild oat shoot fresh weight was reduced 79% when plants were treated with diclofop at 1.12 kg ha−1, but only 46% when treated with diclofop at 1.12 kg ha−1plus tribenuron at 18 g ha−1. Increasing diclofop rate increased control of wild oat but did not overcome the antagonism. Separating the applications of diclofop and tribenuron by as little as 12 s reduced the antagonism by 40%, indicating the importance of close proximity of the two herbicides on the leaf surface for the antagonistic response. The inhibitory effect of diclofop at its target site (acetylCoA carboxylase) was not reduced by tribenuron. Metabolism of 14C-diclofop by wild oat leaves was not altered quantitatively or qualitatively by tribenuron. Tribenuron had no effect on spray retention or absorption of 14C-diclofop by wild oat leaves, and only slightly decreased the total amount of radiolabel translocated out of the treated zone on the leaf. However, tribenuron decreased basipetal translocation of diclofop from the treated zone by approximately 20%. The ability of tribenuron to reduce basipetal translocation of diclofop to meristematic regions of wild oat may be a factor in antagonism.

Repeated use of the preemergence herbicide triallate has selected for wild oat populations that are resistant (R) to field use rates. Field collections and an inbred R line were shown in greenhouse and petri dish dose response experiments to be 6- to 20-fold more tolerant to triallate than susceptible (S) lines. R populations and the inbred line were also resistant (8-fold) to the related thiocarbamate herbicide diallate, as well as to the chemically unrelated postemergence herbicide difenzoquat (60-fold). 14C-triallate uptake and translocation patterns were similar between R and S lines for the first 24 h after application. However, translocation of radioactivity was more rapid in S lines than R lines from 24 through 60 h after application. 14C-difenzoquat uptake was the same in R and S lines 12 h after application, but was 10 to 20% higher in R lines than S lines by 24 through 96 h after application. Similarly, translocation of radioactivity after 14C-difenzoquat application was 7 to 14% greater in R than S lines after 12 h, although translocated radioactivity amounts were not significantly different between R and S lines. The relatively minor differences in triallate and difenzoquat uptake and translocation patterns between R and S lines are most likely not of sufficient magnitude to explain the observed resistance levels.