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Developing New Herbicides to Manage Kochia in Hop Yards

Posted by Marcelo Moretti, Oregon State University | May 12, 2022

Kochia (Bassia scoparia) is a severe weed problem in hop yards in eastern Washington and Idaho. This annual weed is an erect, herbaceous bush-type plant reaching over 6 ft in height if unmanaged. Its deep taproot contributes to its drought tolerance. Kochia is prolific, producing around 12,000 tiny seeds per plant. Abundant seed production allows kochia to quickly populate and achieve high plant densities (Figure 1).

The kochia germination window extends from winter to late summer.

I noticed seedlings in early February 2022, and they likely had emerged weeks before my first observation. Recent eastern WA precipitations has promoted additional flushes of germination in hop fields, and more will occur once irrigation starts.

Figure 1. Hop field infested with Kochia in February 2022 in Yakima Valley, WA.

Early spring cultivation followed by mechanical crowning will control some of these plants, but new seeds will continue to germinate. As the bines grow and develop, herbicide control is the control strategy for these later seedlings. Carfentrazone (Aim), pyraflufen (Venue), and paraquat (Gramoxone) are a few of the options available for kochia control in the hop planting row. These herbicides provide better control of younger plants, which are easier to adequate cover with the product. It is more difficult to achieve adequate coverage during May to June hop training and as the bines exceed 6 to 8 ft in height.

With funding from the Hop Research Council and the Washington Hop Commission, we initiated a project in 2019 to identify new weed management tools in hops for problematic weeds, including kochia. We identified tiafenacil, a postemergence herbicide in the WSSA group 14 mode-of-action that controls broadleaves and small annual grasses. We observed excellent control of kochia, flixweed, and purple mustard, but new kochia seedlings quickly replaced their dead predecessors. In 2022, we are continuing the study to evaluate the suitability of tiafenacil for use during the dormant season, spring pruning, and in-season. Successful research outcomes will give growers more flexibility with this new herbicide when it is most needed. In addition to our crop safety and efficacy work, the IR-4 program is conducting residue work to support a future registration of tiafenacil for hops.

A second objective of the study is to evaluate glufosinate (Rely) use during the dormant and early spring period. Glufosinate is expected to be registered in hops in the coming years. We hope to expand the proposed label, to include more application timings, adjuvants, and rate structure. In 2021, spring glufosinate applications did not affect hop growth or yield in a site in Oregon. In 2022, we will repeat that study at two Oregon and Washington  locations. Initial results are promising for crop safety and for kochia control. The IR-4, Hop Research Council, Washington Hops Commission, and others are evaluating glufosinate residues. We hope to develop practical solutions soon to help growers manage kochia, while meeting export standards for all markets. Our next research plans for hops are to expand evaluation of preemergence herbicides. In future posts, I will share results from non-chemical weed control trials in hops.


I thank the many hop growers who so graciously hosted these studies, and the Hop Research Council, Washington Hop Commission, and the IR-4 program for their support of this work.

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