New herbicides bring additional tools to California rice weed management in 2024

This year brings several new chemical tools to California rice. With many herbicide-resistant species as well as emerging problematic weed species, the new chemistries are a welcome tool for managing resistance and preventing the selection of resistant biotypes.

Last year, we had use of Loyant® CA Rinskor™ active (florpyrauxifen-benzyl) for the full season (registered late in 2022). Loyant®, which is an auxin mimic, is applied as a foliar product. It gives additional options for early-season control of sedges and broadleaf weeds, and although not strong on watergrasses when applied alone, provides added control when tank-mixed with other herbicides for grass control. Based on data collected in 2022-2023, two good tank-mix options for watergrass control are SuperWham®/Stam® (propanil) and Regiment (bispyribac-sodium). It does not control sprangletop.

Cliffhanger™ (benzobicyclon) was just registered in 2024, and is a new formulation of a previously-registered granular product already widely in use in California rice. Since it can be applied as a foliar product, it expands the timing that benzobicyclon can be applied in the flooded system. It can also be applied as a direct-stream application into the water. It is an HPPD-inhibitor, providing a good option for rotation. It controls sprangletop, ricefield bulrush and smallflower umbrella sedge. Additional tank-mix testing will be occurring this season to determine if it might be a good partner in combination with other herbicides for added late-season watergrass control.

The last product recently registered is Zembu™ (pyraclonil). Zembu™ is a granular formulation of pyraclonil, applied pre-emergence or at day-of-seeding into a flooded field. It provides control of smallflower umbrella sedge and broadleaf weeds, and provides suppression of watergrass. As a PPO-inhibitor, it is a new mode of action for watergrass, as the only other PPO-inhibitor registered in California rice only has activity on sedges. It will provide a great rotational option for growers at the beginning of the season, as well as a great partner product (for added control) with other granular into-the-water products.

As always, the label is the law, so make sure to read and follow the current labels for each of these herbicides (found on the manufacturers website or at the Department of Pesticide Regulation's website). Also check in locally with your Agricultural Commissioner's office for training information and any other county-specific requirements.

With these three new options, as well as the currently-registered products, rice growers in California should have a great suite of tools available this year, both for resistance management as well as to prevent the selection of future resistance. For help planning a weed management program, please reach out to your local Rice Farm Advisor.


Original source: UC Rice Notes newsletter • April 2024


By Whitney B Brim-Deforest
Author - County Director, Sutter and Yuba Counties and CE Rice and Wild Rice Advisor
By Gale Perez
Posted by - Public Education Specialist