Weeding and biorational treatments alters thrips, disease, and weed Interactions in an organic onion pathosystem

Thrips (Thysanoptera) feeding causes stunted plant growth and reduction in onion bulb weight. Thrips facilitate transmission of Pantoea spp., the causal agent of center rot of onions, through fecal contamination. In addition, the pathogen is known to survive on over 25 different weed species. Weeds may be hosts for the pathogen and harbor thrips before and during onion growth. Therefore, weed management is likely important for reducing transfer of Pantoea between weeds and onions. We conducted an experiment to examine the effect of current organic management options including weeding and biorational approaches on thrips, disease, and yield in onion systems. The experimental design was a randomized complete block plot design with four replications of each treatment combination. Weed cultivation significantly influenced thrips, where hand weeded plots had significantly lower mean number of thrips and lower disease severity as compared to other cultivation treatments. Disease prevalence decreased with more intensive weeding; however, this trend was not consistent within biorational treatments. For example, biorational treatments had no significant influence on disease severity in the hand weeded plots. Significantly higher onion yield was harvested in the hand weeded plots. Biorational treatments did not significantly affect thrips abundance or onion yield. Hand weeding until harvest was the best approach to managing weeds, thrips, and helped suppress pathogens without the need of biorationals. Our future research will help clarify the influence of weed management techniques on natural enemies of thrips, and their role in the onion pathosystem.