Agroecosystem Approach to Managing Imported Cabbage Worm (Peris rapae)

View the project final report

Commodities

• Vegetables: broccoli, brussel sprouts

Practices

• Crop Production: cover crops
• Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research
• Pest Management: biological control, field monitoring/scouting, integrated pest management, mulches - living
• Production Systems: agroecosystems

Imported cabbage worm (ICM) is a pest of broccoli, cabbage, Brussels sprouts and related plants in the mustard family typically managed with insecticides. Research has shown, however, that several naturally occurring predators and parasites can reduce ICW infestations.

Biodesign Farm has designed a high-plant-diversity, reduced-tillage production system to enhance beneficial insect habitat. The farm has used living mulches between vegetable rows since 1995. In 2004, it began to experiment with greater in-field vegetation diversity and reduced tillage, moving to a new field and setting up organic minimum- and no-till plots. In 2006, it designed an experiment to answer these questions:

• Can ICW be managed without the use of pesticides?
• Can ICW be managed by increasing habitat for predators and parasites?
• What are the most effective predators and parasites for ICW?

The experiment evaluated three treatments: unsprayed control, sprayed bimonthly with a pyrethrum/rotenone mix (chosen to impact predators and parasites while not targeting ICW), and sprayed with Bt when ICW larvae reached a threshold level (chosen to target ICW and have little effect on predators and parasites).

Based on crop yields and ICW damage evaluations, management was possible without spraying chemicals. Broccoli and cabbage yields were high and none was deemed unmarketable because of insect injury. Brussels sprouts in unsprayed plots yielded an 88% marketable crop. Where predator populations were disturbed by spraying rotenone-pyrethrum, ICW damage to Brussels sprouts was highest; where predators were not disturbed, damage was lower.

Introduction

Imported cabbage worm (ICM), a pest of broccoli, cabbage, Brussels sprouts and related plants in the mustard family, is the most common and destructive of the cabbage worms found in the Intermountain West and High Plains regions. Most vegetable producers use insecticides to manage the pest, and even certified organic producers use repeated applications of Bt. Whitney Cranshaw, extension entomologist at Colorado State University, suggests that several naturally occurring predators and parasites, including ground beetles, paper wasps, spiders and parasitic wasps such as Apateles glomeratus, can reduce ICW infestations.

• Can ICW be managed without the use of pesticides?
• Can ICW be managed by increasing habitat for predators and parasites?
• What are the most effective predators and parasites for ICW?
• Does the ICW predator/parasite complex change over the season?
• What is the seasonal variation of ICW in Western Montana?