Ecologically-based Pest Management Strategies for Imported Cabbageworm in Broccoli

View the project final report

Commodities

• Vegetables: broccoli

Practices

• Crop Production: tissue analysis
• Education and Training: on-farm/ranch research
• Pest Management: field monitoring/scouting, integrated pest management
• Production Systems: organic agriculture

Imported cabbageworms (ICW; Pieris rapae) are pernicious insect pests that feed on species in the Brassicaceae (mustard or cruciferous) family. Larvae chew large holes in leaves, can destroy developing heads of broccoli, cauliflower, and cabbage, and contaminate produce with fecal matter. In conventional systems, this pest is controlled with broad-spectrum insecticides, but ICW are notoriously difficult to manage in organic systems. Organic brassica growers traditionally rely on floating row covers or biopesticides, such as Bacillus thuringiensis (Bt) and spinosad, to avoid insect damage. However, though effective, these strategies are expensive and increase labor. Understanding the roles that naturally-occurring defensive compounds, called glucosinolates, found in brassicas, play in mediating plant-insect and plant-insect-parasitoid interactions can provide alternative pest management strategies. Glucosinolates act as an innate immune system of brassicas, and brassicas may respond to insect damage by producing more of these glucosinolates, which may deter further feeding or reduce herbivore fitness. Moreover, glucosinolates may mediate tri-trophic interactions by helping parasitoid wasps find insect hosts, resulting in parasitism and reduction of the subsequent generation of pests. The overarching objective of this research is to improve management strategies of ICW and other caterpillar pests of brassicas by understanding the roles that glucosinolates play in mediating plant-insect and plant-insect-parasitoid interactions. This research will increase yield and quality of brassicas, improving profitability of these crops while preventing non-target effects of pesticides on beneficial insects and pollinators in the environment. A field experiment will evaluate six broccoli varieties to determine differences between broccoli variety and glucosinolate content, insect populations, parasitism, disease, and yield. An experiment replicated in the field and the greenhouse will be conducted to evaluate the effects of insect damage on subsequent feeding, parasitism, and plant response. This project aims to inform growers about: pest management strategies in organic brassica production; basics of natural plant defense in brassica crops; and which broccoli varieties perform best based on yield and natural resistance to disease and insect pests. Based on knowledge imparted at a field day, a presentation, and extension publications, growers can incorporate ecologically-based pest management strategies as part of an IPM program for brassicas.

Varietal Study Objective

1. 1. Determine correlations between broccoli variety and insect populations, parasitism, yield, and head characteristics

Glucosinolate Objective

1. 1. Determine differences between broccoli variety and total and individual glucosinolate levels in the early heading stage of organic broccoli, and correlate to pest pressure

Induced Herbivory Study - Field Objective

1. 1. Determine if previous herbivore damage influences broccoli defense against ICW  by inducing glucosinolates

Induced Herbivory Study - Greenhouse Objectives

1. 1. Determine if previous herbivore damage influences broccoli defense against ICW by inducing glucosinolates

1. 1. Determine if previous herbivore damage affects subsequent ICW feeding and fitness

Performance Targets

Learning Outcome 1: At least 25 participants will attend our presentation at ‘Horticulture Night’, an event at UMN Morris, and at least 25 will attend our field day at Garden Farme where they will learn pest management strategies in organic brassica production; basics of natural plant defense in brassica crops; and which broccoli varieties perform best based on yield and natural resistance to disease and insect pests.

Learning Outcome 2: Researchers and the scientific community will develop a better understanding of the natural defensive system of brassica crops and how it can be utilized to develop a more robust brassica IPM program.

Action Outcome 1: At least 50% of participants at our field day and presentation will utilize broccoli varieties that are more naturally resistant to pests and disease and that have high yields.

Action Outcome 2: At least 50% of participants at our field day and presentation will allow their brassicas to incur some insect damage before applying control methods, such as biopesticide sprays, as part of an IPM program.

Action Outcome 3: At least 50% of participants at our field day and presentation will utilize buckwheat or other flower strips in order to attract and support beneficial predators and parasitoids of brassica insect pests as part of an IPM program.