Dicamba drift as affected by nozzle type, wind speed and spray composition

Abstract

With new releases of dicamba-tolerant crops, it is necessary to understand how technical and environmental conditions affects its application. This dissertation was developed at the West Central Research and Extension Center of the University of Nebraska-Lincoln in North Platte, Nebraska, USA. It was divided in three studies to evaluate dicamba spray drift. The first study evaluated dicamba drift from applications under four wind speeds (0.9; 2.2; 3.6; and 4.9 m s-1). The second and third studies evaluated droplet spectrum and drift from applications of dicamba tank-mixed with drift-reducing adjuvants and glyphosate, conducted at 3.5 and 2.2 m s-1 wind speeds, respectively. The adjuvants used were polymer, ammonium sulfate, vegetable oil and phosphatidylcholine. All applications were performed in a wind tunnel using two standard (XR and TT) and two air induction (AIXR and TTI) 110015 nozzles at 276 kPa pressure. The nozzles were positioned 60 cm above the tunnel floor. Drift potential was determined using a fluorescent tracer added to solutions, quantified by fluorimetry. Round strings were used as drift collectors, positioned 10 cm above the tunnel floor and perpendicular to the wind direction from 2 to 12 m downwind from the nozzle. Each replication consisted of a continuous 10-second application. Droplet spectrum was measured at 6.7 m s-1 using a laser diffraction system. The air induction TTI nozzle produced the lowest percentage of dicamba drift at 2.2, 3.6 and 4.9 m s-1 wind speeds until 12 m, which increased linearly as wind speed increased. Dicamba spray drift from the XR, TT, and AIXR nozzles increased exponentially as wind speed increased. Non-air induction nozzles, in special XR, are not adequated to be used in dicamba applications. Droplet spectrum and dicamba drift depended on the interaction between spray composition and nozzle type. Dicamba associated with vegetable oil and phosphatidylcholine produced finer droplets than dicamba alone when sprayed through the TTI nozzle. The polymer and ammonium sulfate increased the droplet size for all nozzle types. At 12 m from theTTI nozzle, dicamba solutions with or without any adjuvant produced similar drift. Dicamba alone produced coarser droplets than dicamba + glyphosate when sprayed through air induction nozzles. Dicamba tank-mixed with glyphosate reduced the drift if sprayed through the XR, TT, and AIXR nozzles. If sprayed through the TTI nozzle, dicamba alone produced less drift. In general, drift decreased exponentially as downwind distance increased for all spray compositions.