Atrazine Reduces Primisulfuron Transport to Meristems of Giant Foxtail (Setaria faberi) and Velvetleaf (Abutilon theophrasti)

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Abstract
Greenhouse and laboratory studies were conducted to determine the effect of atrazine on efficacy, absorption, translocation, and metabolism of primisulfuron applied to velvetleaf and giant foxtail. Efficacy of primisulfuron was reduced by 18 and 22% when applied at 20 and 40 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1atrazine to velvetleaf. Efficacy of primisulfuron was reduced by 15 and 16% when applied at 30 or 60 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1atrazine to giant foxtail. Foliar absorption of14C-primisulfuron by either weed species was not affected by addition of atrazine to the treatment solution. Atrazine had no effect on metabolism of14C-primisulfuron by either weed species. In the absence of atrazine, translocation of absorbed14C from primisulfuron out of treated leaves of velvetleaf and giant foxtail averaged 19 and 29%, respectively, across sampling times. These values were reduced to an average of 9 and 16% in velvetleaf and giant foxtail, respectively, when14C-primisulfuron was applied in combination with atrazine. The majority of translocated14C from primisulfuron was transported acropetally in velvetleaf and basipetally in giant foxtail. Atrazine significantly reduced14C translocation from primisulfuron to these meristematic sinks in both weed species. Reduced translocation was positively correlated with reduced control of these weeds when primisulfuron was tank mixed with atrazine.