Summary
This field and greenhouse study evaluated four commercially available plant-derived herbicides registered for organic agriculture in managing weeds in apple orchards. Capric/caprylic acid proved most effective, achieving 88% weed cover reduction within 1 hour and 98% within 72 hours in orchard conditions. The authors conclude that capric/caprylic acid and d-limonene, with repeated application efficacy similar to handhoeing but substantially lower cost (US$203–770 ha⁻¹ savings), could help organic producers reduce weed pressure, minimise tillage, and improve profitability.
UK applicability
The findings are relevant to UK organic apple production, where Canada thistle is a significant weed problem and weed management remains the leading production challenge for certified organic growers. However, UK growing conditions, soil types, and the availability and regulatory status of these specific plant-derived herbicides under UK/EU organic standards would require separate validation.
Key measures
Percentage weed cover reduction at 1 h and 72 h post-treatment; perennial weed cover after 3 years of repeated applications; cost per hectare (US$ ha⁻¹); active ingredient concentration (% v/v)
Outcomes reported
The study compared the efficacy and cost of four plant-derived organic herbicides (capric/caprylic acid, d-limonene, acetic/citric acid, and clove/cinnamon oil) against handhoeing and no management control for Canada thistle and total vegetative cover in apple orchards. Greenhouse trials further evaluated weed control response to selected treatments and glyphosate.
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