Research Focus: Rice Weed Management

In-season plot tours and field days keep PCAs and rice farmers apprised of what is going on the field.


I began working in the ag chemistry industry right out of graduate school. My work in rice began in the mid-1980s helping to develop the rice herbicides Whip 1 EC and Whip 360. After 30 years with Bayer CropScience, in 2009, I was offered a position with the Tremont and Lyman Groups where I am the director of technical services. In rice, we primarily focus on herbicide research, but we also conduct fertilizer studies and will be looking at a plant growth regulator to help prevent lodging in the small-grain Japanese varieties, particularly Koshihikari.

Determining Where Herbicides Fit
Weed management is a major concern in California rice because of resistant weed problems and a limited number of weed control materials. Almost every one of our herbicides has at least one weed that is resistant to it. Growers have to mix and match herbicides and make multiple sprays to achieve control. That’s why it is exciting when a product with a new active ingredient, such as Rinskor active, becomes available to us.

In 2017, we saw good results with Rinskor active, which goes out as a foliar spray. In one of our locations, we made an application about 30 days after seeding to control smallflower umbrella plant. It also did a good job on ducksalad and late watergrass. We are hoping to confirm those results this year.

Last year we also continued to learn how to use the newly registered Butte herbicide. This herbicide, with a new mode of action for California rice weed control has good activity on sedges and broadleaf weeds as well as sprangletop. Butte helps with watergrass control, but you still have to come back with another herbicide later in the season. We have demonstrated good watergrass control when following up the Butte application with Granite GR. A propanil or Regiment application can also be used as a mid-season watergrass spray following Butte with good results.

Granite SC herbicide also has shown to have a fit as a mid-season foliar spray in a propanil sequence program. We typically apply propanil 30 to 40 days after seeding for watergrass or sedge escapes. Many times, growers have to apply propanil twice. If weed populations are high enough, the PCA may recommend that propanil be followed by Granite SC because of its activity on watergrass. We are continuing our work with these herbicides in 2018.

Sharing The Knowledge
In season, we generally have two to three plot tours for PCAs and encourage them to bring their farmers to the grower field days. I also try to send out monthly or bi-monthly internal newsletters to let our PCAs know what we are seeing in the field. We conduct a winter meeting strictly for rice farmers that includes our research as well as five or six university speakers. It’s important to let growers know that our technical group is trying to stay on top of anything new coming on the market.

To help in understanding the spread of our herbicide-resistant weeds, we take advantage of a free service provided by the University of California. We collect seeds from weeds we suspect to be resistant and send them to weed scientists Dr. Kassim Al-khatib and Dr. Amar Singh Godar. During the winter, they run a weed seed screen to test for resistance against all the active ingredients. Our PCAs get the results back in March, take them to the growers and then sit down and decide on their weed control program for the coming season.

Even though we have no snowpack this year, the reservoirs are full, allowing us to plant at least 440,000 acres of rice. And the fact that rice prices are up will make it easier to justify expenses for growers to get the best yields they possibly can.

Matt Ehlhardt
Tremont and Lyman Groups
Woodland, California

  • Bachelor of Science degree in plant protection and Master’s degree in plant science with a weed science option, University of Idaho
  • Honarary member and past president of the California Weed Science Society
  • Member of the California Association of Pest Control Advisers (CAPCA) for 35 years
  • Married to wife, Lynn, for 40 years. Three children and four grandsons
  • Enjoys golf, hiking and fishing


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