Start clean, stay clean Extension agent's message is another tool to deal with herbicide resistance

Aaron Esser’s message to growers at a workshop in January was fairly simple — the key to controlling weeds is starting clean and staying clean. Unfortunately, the way to accomplish that is anything but.

“I’ve been doing this for 28 years now. Everyone remembers Maverick Herbicide, right? When that first came out, pow. That stuff just smoked cheatgrass. It made our lives easy. We’ve forgotten about a lot of stuff since then, and what we used to do to control weeds. We’ve gone through 25 years of a lot of easy buttons,” he said. “There’s no more easy buttons.”

Esser’s presentation was part of the Agricultural Marketing and Management Organization’s 2026 winter schedule. He manages the Washington State University (WSU) Wilke Research and Extension farm in Davenport, Wash. The 320-acre farm gets no money from WSU, so Esser has to make planting decisions like a farmer to support the farm and fund research. He uses various crop rotations across the farm to help with research: a three-year crop rotation (no-till fallow, winter wheat, spring cereal); a four-year crop rotation (no-till fallow, winter wheat, broadleaf crop, winter wheat); and a continuous rotation. He told growers they need to look at integrated weed control that includes mechanical, cultural, and chemical components. That might mean some light tillage or changing up when and how chemicals are applied.

“When I talk about chemical, instantly, our minds go to post-emergent applications, because that’s what we’ve been accustomed to,” he said. “We’ve got the sprayers, the tanks, and we just like to get our wheat up, start in the spring in the same field, and go. You’ve got to figure how to change something up.”

Growers should consider pre-emergent/residual herbicide applications, using chemicals with various modes of action. Esser mentioned a new winter wheat release, Rydrych MZ, that has tolerance to high label rates of Metribuzin to help control Italian ryegrass.

One of the main components of Esser’s “start clean, stay clean” philosophy is having a plan. He encouraged growers to create a spreadsheet that tracks what crops were planted where, and what chemicals were applied. He handed out a worksheet and asked growers to pick their worst field and list the previous crops that were planted and the top three worst weeds on it. Then he asked them to consider what they are going to do on that field in the future.

“What you’ve done here (pointing to previous crops) is why you have this (pointing to weeds). Ask yourself what you can do different,” he said. 

One suggestion, if downy brome is a problem, is to seed a little earlier in order to get bigger wheat that can handle a fall or a split herbicide application or even a higher application rate. Esser noted that weed control tends to be more difficult in his three-year rotations.

“I think having what you want to do down on a piece of paper is really important so you and your team are always on the same page,” he said. “Rotation does matter. That cultural piece does matter long term.”

Other weed control research projects taking place at Wilke include using herbicide-tolerant canola in rotations and using residual herbicides along with spot spraying to reduce winter annual grassy weed pressure. Esser has been using a Weed-It spot sprayer on the farm to reduce sprayer fatigue and stay on top of weeds, especially in mid to late-season no-till fallow management and postharvest seed control. He said the piece of equipment has saved him money by allowing him to target just the weeds and lets him use chemicals with different modes of action.

Esser said research in Oregon showed that downy brome growing in winter wheat produced an average of 425 seeds per plant. Under ideal environments, the weed has the potential to produce 125 million plants per acre. Most downy brome seeds remain viable in the soil for two to three years.

“This is 100% a numbers game. One in a million downy brome plants are naturally resistant to Aggressor herbicide. I hate those odds. You need to look at long term viability and profitability over short term profitability and efficiency,” he said. “Don’t give one of those guys a chance to even make it to reproduction.”

Esser can be contacted at aarons@wsu.edu.  

Editor’s note: A few weeks after this AMMO workshop, Esser gave another AMMO presentation in Ritzville that repeated much of the same information. He then spent time talking about winter annual grassy week control. He covered the Clearfield and CoAXium technologies, Aggressor, and Metribuzin.