Summary
Investigator: Sean Swezey, University of California, Santa Cruz, Center for Agroecology and Sustainable Food Systems
Stakeholders: Central California Brussels sprout and other cole crop producers
California leads the nation in Brussels sprout production, producing 90% of the nationally marketed product. However, organic growers have been left out of research efforts to rationalize pest management of the key pests of Brussels sprouts. This is due to the fact that conventional production is almost entirely reliant on organophosphate insecticides. This lack of attention has largely precluded any organic pest control innovation and has created a knowledge gap for improving organic production techniques. The lack of organically compliant pest management tools (both physical and knowledge-based) is exacerbated by the ability of specialist herbivores, particularly Diamondback moth (DBM) and cabbage aphid, to take advantage of Brussels sprouts 9-month production cycle, often causing outbreaks that dramatically reduce yields. As a result, most growers are reluctant to grow Brussels sprouts organically.
We have been working closely with organic farmers who are keenly interested in improving and implementing a biologically-based whole-systems approach to the production of organic Brussels sprouts. The farmers themselves contacted us for assistance and encouraged the preliminary documentation of parasitoids and predators in the field. Our grower collaborators, Larry Jacobs and Billy Rodini, have been directly involved in the development and implementation of our research goals. Experiments are being conducted on five acres of sprouts at Rodini Farms in Davenport, California, and on another five acres of sprouts at Jacobs Farms at Wilder Ranch in Santa Cruz.
In 2009, we collected the parasitoid Diadegma insulare from DBM in organic Brusells sprouts in Santa Cruz County. One half of all the viable field-collected DBM larva and pupa were parasitized by D. insulare. There is great potential for an effective biological control program in organic Brussels sprouts.
In this project we are seeking to collect and rear DBM and identify syrphid larvae from organic Brussels sprouts to determine parasitism rates, syrphid diversity, and relative syrphid species abundance. We will also test the effects of intercropped alyssum and buckwheat on predation and parasitism in diversified organic Brussels sprouts. We seek to advance a more balanced whole systems management approach to DBM and aphid control that would utilize parasitoids and predators by establishing floral resources to provide nectar that is typically lacking in simplified agricultural habitats. This biologically-based solution for suppression of DBM and aphids strives to diminish the damage incurred by these pests, and therefore, improve fresh market yields for organic Brussels sprout and other relevant cole crop growers.
Specific project objectives are:
- Document the degree of parasitism by D. insulare in organic Brussels sprouts;
- Describe the diversity and relative abundance of syrphid larvae in Brussels sprouts;
- Determine the precent parasitism rates when providing nectar-based floral resources in organic Brussels sprouts.
With first year funding from OFRF in 2010, we initiated an investigation of the efficacy and diversity of parasitoids and predators in organic Brussels sprouts. Overall, weekly DBM parasitism by the native Ichneumonid parasitoid Diadegma insulare often exceeded 50% and peaked at 83%.
Syrphid larvae were found to be numerous and effective predators of cabbage aphid. Parasitism of reared syrphid larvae by the Ichneumonid Diplazon sp. was 22.7%. The integration of sweet alyssum with organic Brussels sprouts had a positive impact on syrphid larvae abundance, but did not positively affect DBM parasitism.
In a renewed year of funding (2011), we seek to continue this research and improve our understanding of native biological control in organic Brussels sprouts. This biologically-based solution for DBM and aphid suppression strives to diminish the damage incurred by these pests, and therefore, improve fresh market yields for organic Brussels sprout and other relevant cole crop growers.
A final report describing the results of this project will be posted when complete.