Influence of Carrier Volume and Nozzle Selection on Palmer Amaranth Control

Abstract

ABSTRACT Palmer amaranth is one of the most troublesome weeds in the southeast. Effective control is essential in order to avoid reductions of crop yield. Due to widespread resistance to acetolactate synthase (ALS)-inhibiting herbicides, postemergence contact herbicides are often the only in-season option to control Palmer amaranth in peanut. Lactofen is a postemergence protoporphyrinogen oxidase inhibiting herbicide that is commonly used to control Palmer amaranth in peanut. Adequate spray coverage is essential for lactofen efficacy and nozzle selection may affect coverage. Extended range (XR) and air induction (AI) nozzles were used to evaluate spray coverage on water sensitive cards. XR nozzles provided more coverage than AI nozzles. A factorial treatment structure of carrier volume (94, 187, 281 L/ha), nozzle selection (XR and AI) and application timing (5 to 10 cm or 15 to 20 cm tall weeds) was conducted in 2008 in Williston, FL and in 2012 in Tifton, GA to determine the best strategy for controlling Palmer amaranth with lactofen. Palmer amaranth control was recorded 7, 14, and 21 days after treatment (DAT). Nozzle selection was not significant in field trials as a main effect or as an interaction at any location; therefore data were pooled across nozzle type. However, the carrier volume by application timing interaction was significant at each location. In 2008 at Williston, FL and in 2012 at Tifton, GA application at 5 to 10 cm tall Palmer amaranth with 94, 187, or 281 L/ha provided >90% control. Applications made to 15 to 20 cm tall weeds provided less control. Applications made to smaller weeds provided sufficient control at any carrier volume tested, while applications made to larger weeds were least effective at 94 L/ha. Despite reduced coverage by AI nozzles, nozzle type did not translate to differences in herbicide efficacy in the field. Carrier volume did not affect control of small weeds, but on larger Palmer amaranth, control was reduced at smaller spray volumes. Growers should apply lactofen to smaller Palmer amaranth plants for the most effective control.