Tiafenacil (Gamma, Helm Agro) is now labeled in wine grapes in Oregon, Washington, and Idaho. Tiafenacil is a non-selective postemergence herbicide controlling broadleaves and grasses. It is a new group 14 herbicide, PPO inhibitor, in the N-phenyl-imides chemical family. It is a contact herbicide that provides fast-acting control of weeds and degrades rapidly in the soil. Tiafenacil was developed as a paraquat alternative in Korea.
Tiafenacil (Gamma) is labeled for basal-direct applications in grapes. Recommended rates are 0.5 to 1.5 oz/A of Gamma. For best performance, the adjuvants crop oil or methylated seed oil must be used and ammonium sulfate.
Most annual broadleaves were controlled when treated at less than 5 inches tall. Suppression of Canada thistle was also noted, but plants recovered after treatment. Grasses controlled include Italian ryegrass (<5 inches), annual bluegrass, and other annual grasses. In our studies, higher rates are needed for grass control. Tiafeancil can be tank-mixed with a variety of herbicides. We noticed the best performance when mixing with glufosinate or glyphosate.