Interactions Among Organic Fertility, Mustard Green Manures, and Insect Biocontrol by Entomopathogenic Nematodes

Project Overview

Project Type: Research and Education
Funds awarded in 2004: $138,922.00
Projected End Date: 12/31/2007
Region: Western
State: Washington
Principal Investigator:
Ekaterini Riga
Washington State University
William Snyder
Washington State University

Annual Reports


  • Agronomic: potatoes


  • Crop Production: biological inoculants, cover crops, foliar feeding
  • Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research
  • Farm Business Management: budgets/cost and returns, feasibility study, whole farm planning
  • Natural Resources/Environment: biodiversity, habitat enhancement
  • Pest Management: biological control, chemical control, field monitoring/scouting
  • Production Systems: agroecosystems, holistic management
  • Soil Management: green manures, soil analysis
  • Sustainable Communities: partnerships, sustainability measures


    We evaluated the influence of fertility practices and cover-cropping on the use of insect-attacking, entomopathogenic nematodes (EPNs) as biocontrol agents against the Colorado potato beetle. In two field experiments we released laboratory-reared EPNs into potato field plots treated with either organic or conventional soil amendments (manure and chemical fertilizer respectively). These experiments demonstrated that manure application reduced EPN infection rates on potato beetles, compared to beetle infection rates in plots receiving chemical fertilizer. Factors such as soil pH, predation, and interference may be limiting survival of EPNs in plots fertilized with manure. Survey data show that organic and conventional potato fields have robust endemic EPN populations. Thus conservation of the EPNs already resident in fields may be an important component of a potato beetle integrated pest management program. A series of field cage experiments evaluated the impact of both insect predator and insect pathogen communities on potato beetle control. We found decreasing pest survival with increasing natural enemy diversity. Subsequent analyses demonstrated that improved beetle suppression was driven by the pairing of predators with insect pathogens. In two other large-scale field trials, conducted in each of two field seasons, we found that the EPN species Steinernema feltiae significantly reduced populations of plant-attacking root knot nematodes while also controlling at least one generation of Colorado potato beetle larvae.

    Project objectives:

    1. Investigate inoculative releases of entomopathogenic fungi and nematodes for beetle control.

    2. Determine whether cover crops affect densities of pest & beneficial nematodes and insects.

    3. Examine the combination of entomopathogens, predators, and cover crops for beetle control.

    4. Investigate the economics of adoption of the techniques we are examining.

    5. Distribute cultures of entomopathogens, and information on how they interact with cover crops, to conventional and organic potato growers.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.