Ask the Experts: How to Prevent Cereals Weed Resistance in the Pacific Northwest

For decades, growers have tweaked their spray program to make sure it’s as effective as possible in the never-ending battle to keep weeds at bay. Making adjustments is worth the time, as even immature weeds can pull valuable nitrogen, phosphorus and potassium from the soil. Products such as Axial^® Bold, Axial Star and Talinor^® herbicides are effective weed control tools to be employed thoughtfully and intentionally to provide growers with effective weed control program based on the most prominent weed types in their field.

In the Pacific Northwest, cereal growers often feel that managing herbicide resistance — particularly in grass weeds — is a never-ending task. Dan Maxfield, a Syngenta agronomic service representative based in Washington state, shares what growers in his region are seeing and how he recommends they mitigate resistance on their farms.

Where are you seeing the first signs of herbicide resistance in cereal crops in the Pacific Northwest?

We’re seeing the greatest pressure in annual grass weeds, especially wild oat, Italian ryegrass and downy brome. Resistance issues tend to show up first in high production wheat counties with long histories of repeated herbicide use — particularly areas of northeastern Oregon, southeastern Washington and the Palouse. Fields with continuous cereals or limited rotation tend to show resistance sooner. Herbicide resistance in wild oats and Italian ryegrass was first reported in the early 1990s, and populations have proliferated since then.

How do common crop rotations help reduce resistance pressure and what do you recommend?

Rotations allow growers to:

• Introduce different crop types, enabling new herbicide groups.
• Break up weed life cycles with varying planting dates and tillage practices.
• Use tillage or cultural tactics that aren’t possible in continuous cereals.

My best recommendation is to choose rotations that include broadleaf crops or spring cereals to diversify chemistry, timing and management. Incorporate residual herbicides into fall and spring application timings to control weed populations early with different modes of action and always use full labeled rates to help maximize efficacy on given weed populations.

Herbicide-tolerant wheat varieties have been successfully introduced across the Pacific Northwest to help combat resistant weed populations. They are an excellent tool, but growers should always remember to steward them correctly with proper rotation, herbicide rates and herbicide timings.

How are weather patterns in the Pacific Northwest and spray windows impacting timing and efficacy?

In the PNW, we experience highly variable spring weather — cold snaps, wind and narrow spray windows — which often pushes applications later than might be considered ideal, reducing control and increasing selection pressure. Dry summers followed by late fall rains can also create flushes of weeds that get missed. The result is reduced efficacy and more escapes.

How big of a concern is resistant weed spread via equipment or borders?

It’s a significant concern. Weeds like Italian ryegrass spread easily through combines, trucks and harvest equipment; gravel roadsides and field edges; and hay or straw movement. Even small patches can spread quickly if not contained.

Recommended sanitation steps include:

• Cleaning combines when moving from infested fields.
• Mowing borders before weeds set seed.
• Avoiding driving through patches of weeds.
• Managing waterways and ditch banks proactively.

What scouting and recordkeeping practices do you recommend growers use to make sure their weed-fighting efforts are effective?

Early detection is the best defense. Growers should:

• Scout before and after applications to catch early escapes.
• Flag problem areas with GPS pins.
• Keep year by year herbicide histories for each field.
• Track weed species shifts and areas where control is slipping.

Based on your conversations with growers, what economic worries are most tied to herbicide resistance?

Top concerns include:

• Increased herbicide costs as older programs lose effectiveness.
• Yield loss from escapes in competitive weeds like Italian ryegrass, cheatgrass and wild oats that choke out productive wheat fields.
• Limited herbicide rotation options in dryland areas.
• Higher operational costs from added passes or tillage.

Resistance ultimately threatens long term field profitability.

What is one practical change growers can implement on their farms that could reduce future weed resistance risk?

In a perfect world, we would never rely on the same mode of action twice in a row, especially for high risk grasses. But across the Palouse in wheat and pulse production acres, that is very difficult to accomplish with limited modes of action in our toolbox. The most important strategy for maximizing herbicide efficacy and the grower’s investment is early, timely applications to the weeds and a commitment to cleaning up escapes. Staging applications based on weed size is critical.

Obviously, there are a lot of considerations for cereal growers to balance when it comes to fighting the weeds in front of them this year and the unintended consequences of future herbicide resistance. Regular, thoughtful conversations with crop consultants, chemical reps and (perhaps most importantly) neighboring producers can supply the know-how and peace of mind to confidently implement a proactive spray program.