Control of threadleaf rubber rabbitbrush with herbicides

Abstract

Foliar sprays of 2,4-D [(2,4-dichlorophenoxy)acetic acid]), picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), dicamba (3,6-dichloro-2-methoxy benzoic acid), or clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied in 30 or 150 L of total spray solution ha-1 to threadleaf rubber rabbitbrush [Chrysothamnus nauseosus ssp. consimilis (Greene) Hall & Clem] in Garfield County, Utah. Additional herbicide treatments were applied in 150 L ha-1 in Sevier County, Utah. Herbicides were less effective when applied in 30 L ha-1 than when applied in 150 L of total spray solution ha-1. Mortality was 74 to 87% following applications of 4.4 kg a.e. (acid equivalent) 2,4-D ha-1. Dicamba applied at 3.3 kg ha-1 resulted in 70 to 87% mortality, and picloram applied at 0.8 kg ha-1 resulted in 56 to 79% mortality. The greatest mortalities (84 to 97%) occurred on areas treated with 2.2 kg clopyralid ha-1. Mortality of threadleaf rubber rabbitbrush increased an average of 28, 17, 33, and 27% following applications of 2,4-D, dicamba, picloram, and clopyralid respectively, by using 150 L spray volume. Greatest increases were at the lowest herbicide rates. Applying herbicides in greater amounts of carrier (water) significantly increased both mortality and canopy reduction of threadleaf rubber rabbitbrush for at least 39 months.