Effects of Herbicides Applied Postemergence on Weeds and Sunflowers1

Abstract

Herbicides were applied as postemergence treatments either as early over‐the‐top spray or late‐directed spray to sunflowers (Helianthus annuus L.) for weed control and crop tolerance determinations at Experiment, Ga. Treatments of RP 17623 (2‐tertiobutyl‐4‐(2,4‐dichloro‐5‐ isopropyloxyphenyl)‐5‐oxo‐l,3,4‐oxadiazoline) were applied to sunflowers in the cotyledon, first leaf, and second leaf growth stages. Several herbicides commonly used on other crops were applied late postemergence directed spray to sunflowers when they were 25 to 35 cm tall.were obtained from early postemergence treatments of RP 17623 when applied as over‐the‐top spray at either the cotyledon or the first‐leaf stage of sunflower growth. Weed control results were similar to RP 17623 from several herbicides that were applied as late‐directed postemergence sprays. Early postmergence treatments with RP 17623 caused some early injury to sunflower plants and a reduction in achene oil percent when compared with achenes from untreated plants, but achene yields were not reduced. None of the herbicides applied as late‐directed postemergence sprays injured sunflowers, reduced achene yield, or achene oil percent.