Start Clean, Stay Clean: fall-applied Flumioxazin and Metribuzin application in no-till fallow

November 12, 2026

Broadleaf and grassy weed control in cereal grain cropping systems continue to be a challenge for farmers throughout the Pacific Northwest. Farms continue to experience limited control of downy brome with multiple group 2 herbicide applications, and University weed scientists have documented numerous cases of herbicide-resistant biotypes. Glyphosate-resistant Russian thistle has also become prevalent in our cereal grain cropping systems and horseweed (marestail) and prickly lettuce remain challenging.

In the fall of 2021, two large on-farm trials were established in Adams County on fields going into no-till fallow. Residual herbicides were applied in November with rain in the forecast. Pictures were taken in the spring just prior to the first broadcast application of glyphosate. Residual herbicide applications reduced but did not eliminate the number of downy brome (Bromus tectoram) in the spring of the year, and they decreased but did not eliminate the number of difficult-to-control broadleaf weeds throughout the fallow season. Refer to the photos below for details of specific herbicides and application rates and to view a comparison of the treatment effects the following spring.

A field with many green plants (weeds) are visible among the residue. — Figure 1. The first treatment was a no residual herbicide application check. In this photo of a field with wheat residue, many green plants (weeds) are visible among the residue.

A field of wheat residue with fewer weedy plants than in Fig. 1. — Figure 2. The second treatment was 2.5 oz/ac Valor (flumioxazin) + 16 oz/ac atrazine at 10 gpa. In this photo of a field with wheat residue, this treatment looked clean at the first broadcast glyphosate application (late March to mid-April) but really looked clean at the time of the second broadcast glyphosate application (June). There are fewer weedy plants in the residue when compared to Fig. 1.

A field with wheat residue and fewer green weeds than Fig. 1. — Figure 3. The third treatment was 13.3 oz/ac metribuzin at 10 gpa. In this photo of a field with wheat residue, this treatment looked very clean at the first broadcast glyphosate application (late March to mid-April) but started to break at the time of the second broadcast glyphosate application (June). There are fewer weedy plants in the residue when compared to Fig. 1.