Japanese brome (Bromus japonicus L.) is difficult weed to control on the prairies, due to the limited and minimally effective herbicide options available malt barley growers.

The objectives of this study were to evaluate malt barley tolerance to various herbicide combinations and application timings as well as determine the efficacy of these combinations for Japanese brome control.

This study was initiated in Lethbridge in 2017 and Scott in 2017, 2018 and 2019. The treatments consisted of four herbicides (glyphosate, flumioxazin, pinoxaden, and triallate) applied alone and in-combination at two application timings (fall vs. spring). Flumioxazin was applied at two rates: 70 and 105 g ai/ha (low vs. high). There were 17 herbicide combinations in total.

Single herbicide applications were less effective in controlling Japanese brome than when used in combination. Fall glyphosate, triallate, and post- emergent pinoxaden applications were very ineffective in controlling Japanese brome and ultimately resulted in low yields and to some degree poorer seed quality. Spring applied glyphosate provided great early season weed control with little crop damage, however, Japanese brome regrowth did occur and ultimately resulted in a slightly lower yield compared to applications with a residual component.

Single applications of flumioxazin resulted in slightly better weed control than the non-residual (glyphosate and pinoxaden) applications. Spring applied flumioxazin, averaged over three years at Scott, resulted in a 70% and 58% reduction in Japanese brome compared to fall applications of glyphosate and post- emergent pinoxaden, respectively. Spring applications of glyphosate were comparable to fall flumioxazin and were slightly less effective than spring applied flumioxazin.

The most effective herbicide combination for Japanese brome control was spring applied flumioxazin with pinoxaden and to a greater extend flumioxazin with triallate.

The combination appeared to provide an additive effect as Japanese brome was strongly controlled with this combination in both 2017, 2018, and 2019 and to some degree at Lethbridge in 2017.

Although this combination was the most effective in controlling Japanese brome, the risk of crop injury remains a prominent concern.

For this reason, registration of flumioxazin remains unlikely due to crop injury concerns, regardless of application rate or timing. The most practical and safe practice would be to spray glyphosate in the spring prior to seeding combined with an in-crop herbicide application.