Winter forb control for increased grass yield on sandy rangeland

Abstract

Four separate studies evaluated several herbicides for reducing competition from overwintering weeds on sandy rangeland in west Texas. Air temperature was 10 degrees C with soil moisture adequate for plant growth at herbicide application (0.28 kg ae/ha) on 14 March 1985. Trichlopyr ([3,5,6-trichloro-2-pyridinyl)oxy]acetic acid); 2,4-D [(2,4-dichlorophenoxy)acetic acid]; and dicamba (3,6-dichloro-2-methoxybenzoic acid) plus 2,4-D were ineffective, while picloram 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid); picloram plus 2,4-D; and dicamba alone adequately controlled western ragweed (Ambrosia psilostachya DC.), the major targeted weed. These treatments were repeated on 4 April 1986 when air temperature was 24 degrees C but with dry surface soils. Results were similar to those of 1985, except trichlopyr also controlled western ragweed under the warmer temperature. In another study, various rates of picloram and trichlopyr aerially applied 5 April 1986 showed that 0.07 kg ae/ha of picloram or 0.28 kg ae/ha of trichlopyr reduced (P < 0.05) western ragweed with a corresponding increase in grass production. Picloram more effectively controlled targeted forbs while trichlopyr suppressed sand shinnery oak (Quercus havardii Rydb.) more effectively. Two companion studies also evaluated picloram and picloram plus 2,4-D. In one study 0.28 kg ae/ha of picloram was applied to sand shinnery oak range on 11 March 1985. Grass yield increased from 359 kg/ha in untreated plots to 1,222 kg/ha in treated plots. Grass yield in treated areas remained greater (P < 0.05) for 3 growing seasons post-treatment. Sand shinnery oak plants at the bud burst stage were top-killed by picloram. On 14 March 1985 picloram (0.056 kg ae/ha) plus 2,4-D (0.224 kg ae/ha) was applied to sand shinnery oak rangeland. This treatment reduced forb production with a corresponding increase in grass production the year of application (P < 0.05), but effects did not persist into the second growing season. Picloram plus 2,4-D did not suppress sand shinnery oak.