Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/2006
Publication Date: 7/1/2006
Citation: Sanyal, D., Bhowmik, P.C., Reddy, K.N. 2006. Influence of leaf surface micromorphology, wax content, and surfactant on primisulfuron droplet spread on barnyardgrass and green foxtail. Weed Science 54:627-633. Interpretive Summary: To achieve effective weed control by postemergent herbicides, the herbicides have to come in contact, retain on the leaf surface prior to entering into plant. Leaf surface characteristics of weed species and surfactant play a major role in herbicide efficacy. Scientists from Department of Plant and Soil Sciences, University of Massachusetts and Southern Weed Science Research Unit, Stoneville, MS have examined the several leaf characteristics, and spray droplet behavior on barnyardgrass and green foxtail to understand efficacy of the herbicide primsulfuron on these weeds. These two species differ in leaf surface characteristics and barnyardgrass also has more leaf wax than green foxtain. Adding a surfactant to primisulfuron increased the spread of the herbicide on both weeds, and was further increased by also adding an organosilicone wetting agent. The spread of primisulfuron droplets was higher on the leaf surface of barnyardgrass than the spread on green foxtail when surfactant was added. These results can give insight into the efficacy of this herbicide on these species and how to improve its application.
Technical Abstract: Leaf surface micromorphology and wax content affect the wetting and penetration behavior of foliarly applied herbicides. Laboratory studies were conducted to examine barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and green foxtail [Setaria viridis (L.) Beauv.] leaves, to quantify wax content per unit of leaf area, and to determine the spread area of primisulfuron droplets with and without surfactants on leaf surface of these weed species. Adaxial and abaxial leaf surfaces were examined using scanning electron microscopy and leaf wax was extracted and quantified. The spread of 1 micro liter droplets of distilled water, primisulfuron solution (without surfactant), primisulfuron solution with a nonionic low foam wetter/spreader adjuvant (0.25% v/v), and with an organosilicone wetting agent (0.1% v/v) was determined on the adaxial leaf surfaces of each of the weed species. Stomata and trichomes were present on adaxial and abaxial leaf surfaces in both species. Green foxtail had more stomata per mm2 on the adaxial surface as compared to the abaxial, whereas, barnyardgrass had more stomata on the abaxial surface than on the adaxial. There was no significant variation in the number of trichomes per unit leaf area of green foxtail, and the number of prickles per unit area of leaf was significantly higher in adaxial surfaces than the abaxial, both in young and old leaves. In barnyardgrass the number of trichomes was more on abaxial surface than adaxial. The mean values of the wax content per unit of leaf area in barnyardgrass and green foxtail were 35.91 µg cm-2 and 19.14 µg cm-2, respectively. On both species primisulfuron with a nonionic surfactant had more spread area than that without a surfactant, and the spread was even greater with organosilicone wetting agent. The spread of primisulfuron droplets was higher on the leaf surface of barnyardgrass than the spread on green foxtail when surfactant was added.