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Pacific Northwest Problem Weeds Survey Results

Posted by jenna.osiensky | April 27, 2023

Contributed by Doug Finkelnburg, Area Extension Educator–Dryland Cropping Systems, University of Idaho

This winter we asked small grains producers across the PNW to provide feedback on their most problematic weeds to control and a few details about their cropping systems and practices. This initial stakeholder input activity will help inform research and outreach efforts of the Pacific Northwest Herbicide Resistance Initiative moving forward. The results are informative, if not revelatory, to those working in the weed management space in these regions. I am including some highlights of the survey and thoughts about what we learned.

Survey Highlight #1 – We cast a broad net.

We reached producers at University Extension sponsored winter growers’ meetings in Oregon, Washington, and Idaho as well as through our industry partners’ outreach publications. One hundred full responses were received, representing producers in all the major grain producing areas in the PNW. Respondents represent over 364,000 acres of farmed land.

Survey Highlight #2 – Diverse Cropping Systems and Tillage Practices

While most (69%) of the respondents reported annually cropping, almost half (44%) were in a wheat/fallow rotation and a minority (14%) were using transition cropping or planting one or two times in three years as moisture allowed. An interesting takeaway from this was that almost a quarter (22%) of respondents were farming in multiple cropping systems. About half (54%) of respondents were using conservation tillage (some residue left on the surface) or minimal/no-till. A minority (28%) were using conventional tillage (no-residue). Again, it was interesting to note many (40%) were using multiple tillage practices.

Pinned locations of survey responses.

Figure 1. Approximate locations of survey respondents.

Survey Highlight #3 – Top Problem Weeds by State

Rank (most problematic) Oregon Washington Idaho
1 Russian thistle Downy brome Italian ryegrass
2 Downy brome Russian thistle Kochia
3 Prickly lettuce Italian ryegrass Wild oats
4 Italian ryegrass Prickly lettuce Mayweed chamomile

Of the 16 surveys from Oregon, Russian thistle was hands down the top weed with multiple respondents commenting on the inability to control with glyphosate. Italian ryegrass popped up but only as an issue in the Willamette Valley. In Washington, downy brome and prickly lettuce were spread across the grain producing region with Russian thistle a leading issue in drier areas and Italian ryegrass in wetter areas.

In Idaho, Italian ryegrass is a huge issue in the north as is jointed goatgrass to a lesser extent. Down south, kochia is the top issue in irrigated systems. Interestingly, wild oats are listed as a top problem in each of Idaho’s distinct grain producing regions (N. Idaho rainfed, S. Idaho irrigated, and S. Idaho dryland).

Producers across the three states are noting that glyphosate is not controlling Russian thistle, and Kochia is similarly problematic in eastern Oregon and southern Idaho. Predictably, Sites of Action 1 & 2 issues are noted for downy brome control in all states, although cases were mentioned of glyphosate not controlling downy brome in Washington and Idaho.

It is important to note that producers were asked which herbicides weren’t working to control their main problem weeds, not which weeds were confirmed to be herbicide resistant. However, some disturbing comments were made that should perhaps be used as a “heads-up” for potential future scrutiny. For example, pyroxasulfone was noted as not controlling Italian ryegrass in Oregon as was glyphosate for control of rattail fescue and jointed goatgrass.

What have we learned from this activity? First, many PNW producers have diverse cropping systems and tillage practices within their farming operations. Some irrigated row croppers are using direct-seeding in some legs of their rotations and many direct-seeders also use conservation tillage at times. Many producers with annually cropped ground also have access to wheat/fallow acres. Importantly, we have gained direct feedback from across the PNW about which weeds are causing the most trouble for grain producers. While there weren’t any huge surprises, it is good to confirm what we think we know and periodically double-check we are focused in the most impactful directions.

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