Mulch-based sustainable pest management strategies for green onions

Ecosystem services that can be provided by mulching have not been thoroughly explored as organic farming practices against multiple pests and pathogens. This research project examined three distinct mulching treatments: organic mulch, living mulch, and synthetic soil solarization mulch for their effects on pests and beneficials in green onion (Allium cepa) agroecosystems.  Two field trials were conducted at the Poamoho Experimental Station on Oahu, Hawaii. Green onions were grown in four pre-plant treatments: 1) organic mulch generated by terminating sunn hemp (Crotalaria juncea) cover crop with no-till (SH), 2) soil solarization (Sol), 3) SH followed by soil solarization (SHSol), and 4) bare ground (BG) with insecticides. SH (in 2013 and 2014) and SHSol (only in 2014) treatments were associated with planting insectary borders as living mulch in the green onion crop. Conventional tillage was used in Sol, SHSol, and BG treatments. No-till and organic mulch significantly reduced pest and disease damage by thrips (Thysanoptera: Thripidae), leaf miners (Diptera: Agromyzidae), and purple blotch (Alternaria porri), and increased yields (P ≤ 0.05). Additional yard waste mulch added to SH plot in 2014 improved the suppressive effect against thrips (P ≤ 0.01).  Enhancement of abundance and richness of beneficial organisms in no-till SH than BG were possibly responsible for these pest suppressive effects. Planting of SH (SH, SHSol) out performed no SH (Sol, BG) in reducing thrips and leaf miners damage in 2014 (P < 0.05) when insectary borders were added into SHSol. Although solarization mulch did not suppress foliar pests and pathogens on green onion, it reduced weed management time (P ≤ 0.05) consistently in both years. Overall, SH organic mulch followed by SHSol increased green onion yields compared to BG in both years. These findings have broad implications to develop sustainable pest management practices for other Allium crops.