Sunn hemp and its allelopathic compounds for vegetable production in Hawaii and beyond

Project Overview

Project Type: Research and Education
Funds awarded in 2008: $156,105.00
Projected End Date: 12/31/2012
Region: Western
State: Hawaii
Principal Investigator:
Dr. Inga Zasada
USDA-ARS Horticultural Crops Research Lab
Dr. Koon-Hui Wang
University of Hawaii
Dr. Cerruti R. R. Hooks
University of Maryland
Dr. Ming Li Wang
Jari Sugano
University of Hawaii, TPSS
Dr. Mark Wright
University of Hawaii

Annual Reports

Information Products


  • Vegetables: eggplant


  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, on-farm/ranch research
  • Farm Business Management: agricultural finance, whole farm planning
  • Natural Resources/Environment: biodiversity
  • Pest Management: allelopathy, biological control, cultural control, integrated pest management, mulches - killed, mulches - living, mulching - plastic, row covers (for pests), soil solarization, mulching - vegetative
  • Soil Management: green manures

    Proposal abstract:

    Plant-parasitic nematodes are serious pests of many cropping systems in Hawaii and the continental U.S. Nematicides are too expensive for resource-challenged growers. Further, several have been banned or being scrutinized by the EPA because of human health and environmental concerns. Sunn hemp (Crotalaria juncea) is known for its ability to improve soil nutrient status. However, when incorporated into the soil, it releases allelopathic compounds that are toxic to nematode pests. Further, when used in a strip-till cropping system, sunn hemp (SH) residues that remain on the soil as surface mulch can create a habitat favorable for natural enemies of insect pests and provide a physical barrier to weeds. The main constraint of using non-chemical approaches for nematode management is their short-term effect (usually one cropping cycle) for pest control. However, because of limited land, many small- or intermediate-scale farmers in Hawaii tend to grow similar crops continuously in the same fields within the same rows. One goal of the proposed project is to extend the pest-suppressive effect of SH cover cropping and soil solarization beyond one cropping cycle. Our approach is to use SH as an interplanted cover crop and green manure, solarization and a combination of SH with solarization within the same field. Specific objectives of the proposed research are to: 1. Evaluate the impact of using SH as an organic mulch and green manure, for solarization, and using SH + solarization on nematode, insect and weed pests during two cropping cycles; 2. Examine how SH and solarization impact soil health and pest and beneficial organisms; 3. Identify compounds in sunn hemp that are toxic to nematodes; and 4. Determine the lethal dosage of SH residue required to suppress nematodes, and whether solar heat can enhance its effectiveness. During the project, the ability to enhance the nematode suppressive capacity of SH in combination with solarization will be evaluated under laboratory, greenhouse and field conditions. To determine how to maximize SH pest suppressive potential, nematicidal compounds in SH will be identified in different plant tissues at different stages of its growth. The proposed cropping strategies can be adopted by a wide range of growers and will be tested on commercial farms of different sizes and crop diversities. Thus, we choose to test the most challenging crops listed by the grower participants (eggplant, bittermelon and Italian parsley) as model cropping systems. Project findings will be publicized through field days and workshop events, extension and journal publications, video and website postings. The project will be further evaluated by examining its impact on soil health, beneficial and pest organisms above and below the soil surface, nutrient enhancement, crop yields and profits. Social impacts and direct impacts such as number of persons and acres impacted will also be obtained. Economic analysis will be used to assess the cost-effectiveness of this approach. We anticipate that this project will increase the confidence that growers need to transition into a sustainable and economically viable production system.

    Project objectives from proposal:

    • The overall goal of the proposed research is to prolong the use of farm sites and create production practices that are more sustainable and rely less on off-farm inputs. We propose to better understand the nematotoxic compounds in sunn hemp and how to enhance the nematode suppressive effect of these compounds. Several vegetable crops will be used as model systems during these studies, and the cropping system will be evaluated at three very diverse farming environments. Our specific research objectives are to:Evaluate the impact of using SH as an organic mulch and green manure, for solarization and using SH + solarization on nematode, insect and weed pests during two cropping cycles; Examine how solarization and sunn hemp cover cropping impact soil health pest and beneficial organisms; Identify compounds in sunn hemp toxic to nematodes and quantify their concentrations in different plant tissues and at different growth stages; and Determine the lethal dosage of sunn hemp residue necessary to suppress nematodes, and whether solar heat can enhance its effectiveness. Our extension objectives are to disseminate our findings to stakeholders, help growers transition to more sustainable practices and evaluate the impact and adoption level of our program.
    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.