OPTIMAL GLYPHOSATE APPLICATION TIME FOR CONTROL OF FOXTAIL BARLEY (HORDEUM-JUBATUM)

Optimal time of application of the isopropylamine salt of glyphosate for long-term control of foxtail barley was studied near Delta Junction, AK in 1992 and 1993. Applications of either 0.6 or 1.1 kg/ha of glyphosate with 2.2 kg/ha of ammonium sulfate and 0.5% (v/v) nonionic surfactant were made to different foxtail barley plots at approximately 2-wk intervals from May to September, Control was rated in July of the year following application, The 0.6 kg/ha rate produced less than or equal to 60% control on all application dates, At 1.1 kg/ha, foxtail barley control was best from applications made between early August and mid-September, May and mid-June applications provided up to 80% control in 1993 but less than or equal to 50% control in 1992, For both rates, applications made from late June through July, during foxtail barley flowering and seed fill, consistently provided little control (< 50%). Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; foxtail barley, Hordeum jubatum L. #(3) HORJU.