Timing of Herbicide Applications for Control of Larkspurs (Delphiniumspp.)

Abstract

Timing and application rates of herbicides were evaluated for control of duncecap and tall larkspur on mountain rangelands. Picloram, triclopyr, glyphosate, and metsulfuron were applied at three rates during three growth stages (vegetative, bud, and flower) to evaluate the rate by growth stage interaction. Picloram was equally effective over all growth stages when applied at 1.1 or 2.2 kg ae ha−1. Metsulfuron was most effective when applied in the vegetative stage; 0.035 kg ai ha−1killed 95% of duncecap larkspur, but 0.14 kg ha−1was required to kill the same percentage of tall larkspur. Glyphosate at ≤ 2.2 kg ai ha−1was least effective when applied in the flower stage compared to earlier growth stages. Triclopyr showed variable control at rates from 1.1 to 4.5 kg ae ha−1.