Weed management in organic dryland wheat production in the Pacific Northwest

Abstract

Growth in demand for organic small grains has increased interest in producing certified organic crops in the semiarid US Pacific Northwest. The region is well-suited for small grain production, and there is a strong market for organic food products on the US West Coast. However, many growers encounter significant and persistent challenges with weed management, particularly management of perennial weeds such as Canada thistle [Cirsium arvense (L.) Scop.] and field bindweed (Convolvulus arvensis L.), but also common winter and spring annual grass weeds including cheatgrass (Bromus tectorum L.) and wild oat (Avena fatua L.). Coupled with the need to minimize soil disturbance, weed management can become nearly intractable and production limiting. From 2004 to 2024, several short and intermediate studies have been conducted to assess weed control tactics and crop rotation effects on weed management. Lessons learned include incorporating alfalfa (Medicago sativa L.) and spring barley (Hordeum vulgare L.) into rotations for suppression of field bindweed, or alfalfa and winter triticale (x Triticosecale Wittmack) for suppression of Canada thistle. Optimization of cultural inputs, particularly seeding rate, are critical for each crop in rotation. Animal integration and new crops such as quinoa (Chenopodium quinoa Willd.) are alternatives to conventional crops and potentially profitable. Incorporation of precision mechanical and chemical systems is feasible in narrow-row cereals, and when combined with crop rotation, it could reduce or eliminate the need for repeated transitions back to convention production for organic growers.