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

    Proposal abstract:

    The Western SARE grant was received in Fall 2004. Our project has 5 objectives: 1) to survey the Columbia Basin for entomopathogenic nematodes (EPNs) for potential control agents, and also nematode’s soil competitors, 2) to investigate inoculative releases of entomopathogenic nematodes under conventional and organic fertility, 3) to determine whether a combination of two entomopathogenic nematodes with different host finding behaviors increases Colorado potato beetle (CPB) control, 4) to determine whether mustard green manures in the fall preceding potato crops impacts entomopathogenic nematode populations, and 5) to determine whether mustard green manures affect densities of alternative prey and pupation of Colorado potato beetle. In 2004 we made progress on objectives 1 and 4. In order to investigate objective 1, we conducted a survey of EPNs in the Columbia Basin of Washington. We collected entomopathogenic nematodes from three organic potato fields, five conventional fields, and three conventional fields where potatoes followed plantings of mustard green manure. These fields were located near Moses Lake, Othello, and Prosser, WA. The greater wax moth, Galleria mellonella, is highly susceptible to entomopathogens and was used as sentinel prey in field bioassays. Groups of five larvae were placed in mesh sacks (10 sacks/field) and buried at a depth of 10-15 cm, similar to CPB pupation depth, for 48 hrs. The sacks were then collected and monitored for nematode infection over 2 weeks. The analysis of the 2004 survey suggests that EPNs are common in potato fields in the Columbia Basin (35% infection rate of sentinel prey). Thus, conservation of resident EPNs could form one component of a potato beetle IPM program. However, our field survey data suggested that EPN densities were lower in fields following mustard green manures used for the control of plant feeding nematodes. Thus, there may be a conflict between the use of green manures for the control of plant parasitic nematodes and conservation of resident EPNs. Finally, organic and conventional fields housed similar EPN densities, although species diversity appeared to be higher under organic management. So far, the nematodes have been identified to genera; however, the EPNs need to be identified to species to get a more complete understanding of EPN biodiversity. We conducted a series of laboratory experiments in Petri dishes to determine whether mustard affects the efficacy of entomopathogenic nematodes (objective 4). As seen in field surveys, there was a decrease in parasitism when mustard green manure was present. A series of 2x2 completely randomized factorial designs were used (mustard ± X nematode ±) giving a total of 4 treatments. Five G. mellonella larvae were placed in Petri dishes with filter paper, 1ml of treatment solution (either a water control, or mustard extract diluted in water), and 50 infective EPN juveniles (Heterorhabditis bacteriophora) per larva. The response variables were the percent of larvae dead and infected. These laboratory assays support our field survey work, with decreasing EPN infection in the presence of mustard extract. The next step in this effort is to screen several commercially available EPN species to determine levels of susceptibility between and within genera.

    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.