Foxtail Barley Heading, Yield, and Quality as Influenced by Growth Regulators and a Desiccant

Foxtail barley (Hordeum jubatum L.) mixed with other forages harvested after heading or accumulated material bears awns that mechanically injure livestock and game animals upon consumption. This study examines the use of several growth regulators and a desiccant on supression of heading of foxtail barley and subsequent changes in forage yield and quality. During 1979 and 1981, stands of foxtail barley on two subirrigated, lowland sites (Ustic Torrifluvent and Typic Ustifluvent soils) were treated at different stages with growth regulators, at different rates, and with a desiccant. Effects of treatments were determined on number of heads, dry matter (DM) yield, estimated in vivo DM digestibility, and crude protein concentration of the foxtail barley forage. Treatments (kg ai. ha⁻¹) were as follows: metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] at 2.8, 5.6, and 8.4; mefluidide [N-(2,4-dimethyl-5-[[(trifluoromethyl)-sulfonyl]amino]phenyl)a cetamide] at 0.28,0.56, and 0.84; maleic hydrazide (MH) [1,2dihydro-3,6-pyridazinedione] alone at 4.5; MH at 3.36 with chlorflurenol [methyl-2-chloro-9-hydroxyfluorene-9-carboxylate] at 1.12; and paraquat [1,1'dimethyl-4,4'-bipyridinum dichloride] at 0.9 with 0.5% (v/v) X-77 (spreader-activator). Paraquat and MH plus chlorflurenol were the only chemicals that consistently reduced heading of foxtail barley (83 to 98%) both years. Maleic hydrazide plus chlorflurenol also consistently reduced heading when applied either 1 or 3 weeks after the first floral primordia developed. Reducing heading more than 90% reduced DM yield more than 50% the 1st year and 80% the 2nd year. Reducing heading more than 90% increased estimated in vivo DM digestibility and crude protein from 10 to 90 g kg⁻¹ units both years depending upon the chemical, and rate, and date of application. The 1st year's results indicated that metolachlor and mefluidide should be applied within a week of when the first floral primordia of foxtail barley develops for maximum control of heading but additional research should be done to confirm this. Moisture stress of foxtail barley during May of 1981 limited the effectiveness of the growth regulators in controlling heading the 2nd year.