Submitted to: Weed Biology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2007
Publication Date: 1/1/2008
Citation: Sanyal, D., Bhowmik, P.C., Reddy, K.N. 2008. Effect of surfactants on primisulfuron activity on barnyardgrass and green foxtail. Weed Biology and Management 8:46-53. Interpretive Summary: Effectiveness of a particular herbicide for a given weed may be altered by the use of a chemical called a surfactant. Scientists from Department of Plant and Soil Sciences, University of Massachusetts and Southern Weed Science Research Unit, Stoneville, MS have conducted studies to determine the effect of the herbicide primsulfuron on two weeds barnyardgrass and green foxtail when combined with surfactants. Two classes of surfactants a non-ionic surfactant (NIS) and organonosilicone wetting agent (OWA) were compared against the water application of the herbicide. Barnyardgrass was poorly controlled with this herbicide reghardless of surfactant. However green foxtail control was improved by 50% with NIS and about 100% with OSA. Examination of leaves using a scanning electron microscope indicated a more uniform coverage of green foxtail with the surfactants. Other tests indicated that these surfactants also increased the contact angle of the droplet with the leaf surface. The mechanism for increased primsulfuron control of green foxtail by using surfactants has been described.
Technical Abstract: Laboratory and greenhouse studies were conducted to (1) measure the contact angle of primisulfuron droplet with and without surfactants on leaf-surface of barnyardgrass and green foxtail, (2) determine primisulfuron activity on these weed species, and (3) examine spray deposit of primisulfuron with and without surfactants on the leaf surface of green foxtail using scanning electron microscopy. A non-ionic surfactant (NIS) and an organosilicone wetting agent (OWA) were used at 0.25 and 0.1% (v/v), respectively. The contact angles of 1-'l droplets were measured on the leaf surface using a goniometer. The activity of primisulfuron on barnyardgrass and green foxtail was assessed 3 wk after treatment (WAT) based on visual injury and fresh weight. Contact angles of 1-µl droplet of primisulfuron on the adaxial surface of barnyardgrass and green foxtail leaves were 152° and 127°, respectively, when applied without surfactant. Addition of either surfactant markedly reduced contact angle and contact angle was lowest when OWA (<2°) was added to primisulfuron in both weed species. Percent injury of barnyardgrass was very low (4 to 5%) even at higher rate (80 g ai/ha) of primisulfuron, regardless of surfactant. Primisulfuron at 40 g/ha controlled 43% green foxtail without surfactant and the control increased to 65% with NIS and 83% with OWA. Primisulfuron with surfactant markedly reduced fresh weight of green foxtail compared with primisulfuron applied alone, regardless of primisulfuron rate and surfactant type. The scanning electron micrographs showed that uniform deposit of spray droplets with close contact of droplets to the leaf epicuticular surface in green foxtail in the presence of surfactant compared with no surfactant. Enhanced primisulfuron activity on green foxtail with surfactants was due to reduced contact angle and uniform deposition of primisulfuron spray droplets on the leaf surface.