Celia Corado
Major Professor: Dr. Stephen Meyers
MS DEFENSE SEMINAR
March 9, 2026 @ 2:00 pm
Room: HORT 222 or via Teams
Sustainable Weed Management Strategies for Small-Scale Agriculture: Physical Suppression in Onion Production and Bioherbicide Potential of Black Soldier Fly Frass
Abstract: Indiana small farm operators prefer that sustainable weed management include alternatives to conventional herbicides, single-use plastic mulches, and intensive soil disturbance. This thesis investigated two complementary approaches. The first study evaluated five pre-plant treatments (clear tarping followed by either black silage tarping, flame-weeding, glyphosate, or caprylic acid, and a bare ground control) combined with two post-emergence cultivation tools (tine harrow and Q-hoe) in transplanted onion production at Purdue University Student Farm in 2025. The second study examined black soldier fly frass (BSFF) tea suppression of barnyardgrass (Echinochloa crus-galli), redroot pigweed (Amaranthus retroflexus), and velvetleaf (Abutilon theophrasti) seed germination through three laboratory experiments conducted between 2024 and 2025. In the onion field trials, clear tarp followed by silage tarping provided superior season-long weed suppression, required minimal hand-weeding labor, and achieved highest onion yield. Clear plastic increased soil temperature by 3.0°C during the pre-plant period, promoting weed seed germination, while subsequent black silage tarp application terminated emerged seedlings through occultation. Glyphosate effectively controlled weeds but reduced onion yield due to phytotoxicity. Post-emergence cultivation tool had no significant effect on weed density, labor requirements, or yield. Laboratory bioassays demonstrated that BSFF tea weed seed germination suppression was concentration-dependent with complete inhibition at 0.12 g/mL-1 and above for all species. Species susceptibility varied, with redroot pigweed most susceptible, velvetleaf intermediate, and barnyardgrass most tolerant. Neutralizing frass tea pH did not significantly affect weed seed germination suppression. However, frass tea suppressed weed seed germination significantly more than electrical conductivity-matched saline solution in barnyardgrass and velvetleaf, suggesting that phytotoxic compounds beyond osmotic stress contribute to suppression. These results demonstrate that clear followed by silage tarping offers small-scale organic onion growers an effective non-chemical pre-plant weed management strategy, while BSFF tea shows potential as a pre-emergence bioherbicide pending field validation and impact assessment.