Many organic vegetable farmers cultivate for weed control through the crop’s “critical weed-free period” and neglect later-emerging weeds, a practice that mitigates current year yield losses but allows the soil’s weed seed bank to build. This project sought to reduce weed populations in organic vegetable fields by combining weed seedbank management (preplant tarping, pre-emergence flame weeding, and later-season manual weeding to prevent seed set) with advanced and stacked within-row cultivation tools.

Four-year cropping systems trials were conducted at research stations in Maine and Michigan and additional field trials were conducted on 31 working organic farms.  Findings included:

• Seedbank management prevented a buildup in weed seed populations.
• Stacking finger weeders with tine weeders or disk hillers, or alternating hillers with finger weeders improved within-row weed control over single tools or other combinations.
• Selecting and adjusting tools for crop species and size improves weed kill and limits crop damage, which was negligible in snap bean and acceptable in beet at the 4-6 leaf stages.
• Burial (moving soil into the row) is more effective than uprooting (moving soil away from the row) for grass weeds in weakly-rooted crops like young carrots.
• Larger carrot seeds and cultivars with tall early growth (e.g.,‘Bolero’) improves yield and tolerance to cultivation.
• Uprooting is more effective against broadleaf weeds in well-established crops.
• Rolling seedbeds increased compaction and reduced efficacy of flextine weeding.
• Compost amendments sometimes improve crop growth and cultivation efficiency.
• Participant farmers benefited from the collaboration and often adopted new tools and strategies, but they found it difficult to keep up with the data collection required for rigorous on-farm trials.