Inconsistent control of barnyardgrass with bispyribac may be alleviated through adjuvant technology. Experiments were conducted to determine the effect of adjuvant and urea ammonium nitrate (UAN) on absorption and translocation of bispyribac in barnyardgrass. Additional experiments were conducted to determine when maximum absorption and translocation occurred with the use of a methylated seed oil/organosilicone adjuvant (MSO/OSL) plus UAN (0.37 L ha⁻¹ and 2% v/v). In the initial experiment, ¹⁴C-bispyribac–treated leaves, nontreated leaves, and roots were collected 6 and 24 h after application. Absorption was greatest with tank-mixed MSO/OSL (0.37 L ha⁻¹) plus UAN (2% v/v) and the proprietary blend of MSO/OSL/UAN (2% v/v) at 80 and 74% of applied ¹⁴C-bispyribac, respectively. Translocation to nontreated leaves and roots was also highest with these treatments. Increased translocation appeared to be due to greater herbicide absorption, not an increase in translocation rate. The addition of 32% UAN to MSO/OSL and nonionic organosilicone (OSL/NIS) adjuvant systems resulted in a four to fivefold increase in absorption compared with treatments without UAN. Recovery of ¹⁴C-bispyribac in additional experiments generally decreased as time after application increased; however, recovery was 86% or greater for all time intervals. By 12 h after application, 68% of applied ¹⁴C-bispyribac was absorbed. At this time, ¹⁴C-bispyribac was partitioned within the plant in the following manner: 48% in the treated area, 10% in leaf tissue from treated area to tip of the treated leaf, 1.9% in leaf tissue from treated area to collar region of the treated leaf, 1.6% in remaining leaves from collar of treated leaf upward, 5.3% in remaining leaves from collar of treated leaf downward to soil line, and 0.7% in the roots. These data indicate that maximum absorption was achieved within 12 h with a tank mix of MSO/OSL and UAN or the MSO/OSL/UAN blend.

Nomenclature: Bispyribac; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG