2019 ASHS Annual Conference

Weeds are a major issue in organic cropping systems, and farmers need a variety of tools to manage them. Preventative cultural practices, mechanical cultivation, and hand weeding are common approaches to weed control in organic vegetable and specialty crop systems, but each management approach has its limitations. Twenty percent acetic acid (a.k.a. horticultural vinegar) is one of few desiccant herbicides available to organic growers, but it is only somewhat effective on weeds ≤10 cm in height. In addition, it is expensive, which further limits its usefulness. Our objective was to evaluate a promising new option for non-synthetic weed control, a mixture of capric and caprylic acid (CA), which is allowable in organic systems “with restrictions” and rapidly burns down weeds via desiccation. We compared CA to acetic acid (AA) as a desiccant herbicide for weed control effectiveness and cost in an organic sweet corn system. A randomized complete block design with five weeding treatments was used for a field study in northern Colorado. The treatments were an untreated weedy check, a weed-free check, a single hand hoeing at the 4-leaf collar/5-leaf collar stage (V4/V5), AA applied at V4/V5, and CA applied at V4/V5. Both AA and CA were applied as a simulated shielded spray at 20% v/v (undiluted) and 9% v/v, respectively. Two weeks after application CA exhibited 78% weed control and AA exhibited 56% weed control compared to the untreated check. Moreover, CA was able to control weeds ≤23 cm in height, which is more than twice the size of weeds AA can effectively control. The single hand hoeing at V4/V5 treatment provided 66% weed control at two weeks. CA was about half of the cost of AA at $95/25 m² and $171/25 m², respectively. Neither CA nor AA reduced sweet corn ear number, but the average ear weight of the CA treatment (0.21 kg) was significantly higher than the untreated weedy check (0.18 kg). This study demonstrates that CA is more affordable and effective than AA for non-synthetic weed control in organic production. As such, CA may be a viable option to explore further for high-value specialty crop producers wanting to include an effective desiccant herbicide for weed management in their organic system plans.