Absorption and activity of foramsulfuron in giant foxtail (Setaria faberi) and woolly cupgrass (Eriochloa villosa) with various adjuvants

Greenhouse and laboratory studies were conducted to examine the activity and foliar absorption of foramsulfuron in giant foxtail and woolly cupgrass with various adjuvants. Adjuvant selection was important for giant foxtail control. Foramsulfuron provided 90% or greater giant foxtail control with the addition of methylated seed oil (MSO) or MSO plus 28% urea ammonium nitrate (UAN). When a crop oil concentrate (COC) or a nonionic surfactant (NIS) was added to foramsulfuron, giant foxtail control was only 20%. However, when 28% UAN was added to COC or NIS, control was increased to 90 and 85%, respectively. Foramsulfuron absorption and control were closely related in giant foxtail. Foliar absorption of 14 C-foramsulfuron in giant foxtail ranged between 35 and 90% 24 h after treatment (HAT) depending on adjuvant selection. The rate of absorption was greatest when MSO plus 28% UAN was added to foramsulfuron and absorption was maximized 4 HAT. Foramsulfuron absorption in woolly cupgrass reached its maximum levels 2 HAT with all adjuvant combinations. Although the rate of foramsulfuron absorption was quicker in woolly cupgrass, absorption trends by adjuvants were similar to those in giant foxtail. Maximum absorption of 14 C-foramsulfuron in woolly cupgrass was 84% with the addition of MSO plus 28% UAN. However, even with high levels of absorption, woolly cupgrass control with foramsulfuron was poor and may be related to rapid metabolism to nonphytotoxic compounds.