Summary
This field and greenhouse study evaluated four commercially available, USDA-certified organic herbicides derived from plant sources for Canada thistle management in apple orchards. Capric and caprylic acid (CAP) demonstrated superior efficacy, reducing weed cover by 98% within 72 hours, whilst offering significant cost savings (US$769.50 ha⁻¹ less than mechanical hoeing) with comparable long-term perennial weed suppression after three years of repeated applications. The findings suggest that natural herbicides, particularly CAP and d-limonene, could reduce tillage pressure and improve profitability in organic production systems.
UK applicability
The results are directly applicable to UK organic apple and horticultural production, as Canada thistle is a significant weed species in British orchards and the herbicides tested are approved under UK organic standards. However, UK growing conditions, labour costs, and weed pressure profiles may differ from those in the US trial sites, warranting on-farm validation before widespread adoption.
Key measures
Weed cover reduction percentage at 1 h, 72 h, and 3 years post-treatment; cost per hectare; concentration of active ingredients in greenhouse trials
Outcomes reported
The study compared the efficacy and cost of four plant-derived organic herbicides (capric/caprylic acid, d-limonene, acetic/citric acid, clove/cinnamon oil) against mechanical hoeing and untreated controls for managing Canada thistle and vegetative cover in apple orchards over 3 years. Weed cover reduction, perennial weed suppression, and cost per hectare were measured.
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