Field experiments in 2001 and 2002 at Stuttgart, AR, demonstrated cyhalofop applied POST controlled propanil-susceptible barnyardgrass, propanil-resistant barnyardgrass, and broadleaf signalgrass 67, 65, and 71%, respectively 28 days after treatment (DAT). Halosulfuron applied 1 d before cyhalofop or applied in a tank-mixture reduced broadleaf signalgrass and propanil-resistant or propanil-susceptible barnyardgrass by 35 to 59 percentage points. Triclopyr applied 5, 3, or 1 d before, or mixed with, cyhalofop reduced control of propanil-resistant and propanil-susceptible barnyardgrass, 16 to 41 percentage points, respectively. Triclopyr applied 1 d before cyhalofop or combined with cyhalofop reduced broadleaf signalgrass control 38 and 18 percentage points, respectively compared with cyhalofop alone. Propanil reduced cyhalofop grass control only when mixed with cyhalofop. Application timings, averaged across halosulfuron, propanil, and triclopyr, made 1 d before cyhalofop or tank-mixed with cyhalofop reduced grass control more compared with other application timings made before or after cyhalofop. Barnyardgrass absorption of 14C-cyhalofop alone or mixed with propanil was 86 and 75%, respectively, with 14C-cyhalofop translocation being reduced by 10-fold when propanil was mixed with cyhalofop. Reductions in cyhalofop translocation in combination with propanil may have partially explained the reductions in grass control observed in the field.
Nomenclature: Cyhalofop; halosulfuron; triclopyr; propanil; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. # BRAPP; rice, Oryza sativa L. ‘Wells’.
Additional index words: ACCase, application timing, herbicide absorption, herbicide translocation, herbicide interaction, propanil-resistant barnyardgrass.
Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase; COC, crop oil concentrate; DAT, days after treatment; HAE, hours after exposure; LSS, liquid scintillation spectrophotometry; PS, photosynthetic; SA, synthetic auxin.
