Soil moisture, relative humidity, and bentazon affect imazethapyr absorption and translocation in common ragweed (Ambrosia artemisiifolia)

Soil moisture, relative humidity (RH), and the addition of bentazon were examined for effects on absorption and translocation of ¹⁴C-imazethapyr in common ragweed. When common ragweed was growing under conditions of low soil moisture (-300 kPa), absorption of ¹⁴C-imazethapyr was reduced from 51 to 42%. Translocation of ¹⁴C-imazethapyr was not affected by soil moisture. In the absence of bentazon, absorption and translocation of ¹⁴C-imazethapyr was similar at 65 and 85% RH 48 and 168 h after treatment. Bentazon decreased absorption of ¹⁴C-imazethapyr from 61 to 26% at 65% RH and from 65 to 57% at 85% RH 168 h after treatment. Bentazon decreased translocation of ¹⁴C-imazethapyr from 35 to 9% at 65% RH and from 30 to 21% at 85% RH when averaged over time. This reduction in the absorption and translocation of ¹⁴C-imazethapyr when bentazon was added may result in a reduction in common ragweed control compared to imazethapyr alone when RH is 65% or lower.