No-till Organic Cropping Systems for the Dryland Pacific Northwest
Project Director
Lynne Carpenter-Boggs
Year Funded
2020
Award Number
2020-51106-32484
Funded Institution
Washington State University
Grant Program
ORG (Organic Transitions)
USDA NIFA Report
Project Overview
This project aimed to make organic no-till direct-seeded crop production feasible for the Palouse region of the interior Pacific Northwest through an innovative approach to integrated weed management. The strategy utilizes sensor-guided selective application (WEED-IT technology) of National Organic Program (NOP)-allowed herbicides based on caprylic and capric acids and d-limonene, and winter pea rotation crops using food grade cultivars to enhance economic return. Trials were conducted in WA and ID comparing NOP-allowed herbicide products and several winter pea varieties. Greenhouse studies were conducted to assess efficacy, crop damage, and other non-target impacts of the herbicides.
Two new NOP-allowed herbicides, Suppress® (7% caprylic + capric acids) and Avenger® (14% d-limonene) gave 85-100% burndown weed control over five years of trials, compared to 32-84% for two older products AllDown® (12% acetic + citric acids) and Weed Zap® (4.5% clove + cinnamon oils). Caprylic/capric acid was most effective against broadleaf seeds and cost only 1/3 as much as hand weeding, while d-limonene was most effective on grasses and similar to hand weeding in cost. Using the same product for five years caused shifts in weed floras, illustrating the need for multi-tactic weed IPM.
Extreme weather has impacted the IPM field trials, with drought in 2021 and 2023 resulting in poor weed competition from the winter pea crop, and excessive summer rainfall rendering both NOP herbicides and manual weeding ineffective.
Farmer Takeaways
(1) Newer NOP-compliant herbicides based on caprylic + capric acids (Suppress®) and d-limonene (Avenger®) outperformed older acetic acid and essential oil products.
(2) These products can be as effective and less costly than hand-weeding, and have even worked well against field bindweed and Canada thistle in new orchard plantings.
(3) Sensor-guided selective application technology uses far less herbicide per acre, thereby reducing direct costs and risks to non-target organisms.
(4) Repeated use of the same product will shift weed flora toward less susceptible species; thus, organic herbicides should be one component of an integrated weed management strategy.
Project Outputs
Appleby, A.B. and L, Carpenter-Boggs. 2021. Efficacy and Economic Viability of Organic Herbicides. ASA, CSA, SSSA International Annual Meeting in Salt Lake City, UT. November 2021.
Webinar: Soil Health Sit Down: Organic Herbicides and Their Potential Role in Palouse Agriculture | Palouse Conservation District