Influence of Spray Tip and Spray Volume on the Efficacy of Imazapic and Imazethapyr on Selected Weed Species

Aims: To evaluate control of weeds commonly found in peanut fields when using imazapic or imazethapyr applied post emergence with different spray tips and at different spray volumes.
Study Design: Experimental design was a randomized complete block with three replications and a seven spray volume (47, 71, 94, 117, 140, 164, and 187 L ha-1) or a six spray tip [110015 flat fan (FF), 110015 Turbo TeeJet (TT), 110015 drift guard (DG), 110015 air induction (AI), 110015 turbo drop (TD), and 110015 extended range (XR)] by two herbicides (imazapic or imazethapyr) factorial arrangement of treatments.
Place and Duration of Study: Field studies were conducted during the 2006 and 2007 growing seasons in the south Texas and in the Texas High Plains peanut growing regions.
Methodology: Spray volumes and spray nozzle tips were compared for control of the annual grasses Urochloa texana (Buckl.) R. Webster, and Digitaria ciliaris (Retz.) Koel. and the broadleaf weeds Amaranthus palmeri L., Cucumis melo L. var. DudaimNaud., Ipomoea lacunose L., Sida spinosa L., Solanum elaeagnifolium Cav., Tribulus terrestris L., and Proboscidea louisianica (Mill.) Thellung.
Results: U. texana control was not affected by spray volume but D. ciliaris control was affected. With D. ciliaris, as spray volume increased, herbicide efficacy decreased. Spray volume did affect A. palmeri efficacy. In both years at the High Plains location, a spray volume of 47 L ha-1 provided better control than 187 L ha-1. C. melo, I. lacunose, T. terrestris, and S. spinosa control with both herbicides decreased as spray volume increased. Annual grass control was not affected by spray tip application while A. palmeri efficacy was reduced at one location with 110015XR nozzle tips. C. melo, I. lacunose, and S. spinosa control was not affected by spray tip; however, 110015TT and 110015FF provided the best control of S. elaeagnifolium and P. louisianica, respectively.
Conclusion: Depending on weed species the amount of carrier volume and spray tip can affect weed efficacy under similar conditions as found in this study.