Cropping Systems to Control Tropical Soil-Borne Pests in Dryland-Grown Taro

Project Overview

Project Type: Research and Education
Funds awarded in 2003: $257,827.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $28,875.00
Region: Western
State: Hawaii
Principal Investigator:
Dr. Susan Miyasaka
University of Hawaii

Annual Reports


  • Vegetables: taro


  • Education and Training: demonstration, on-farm/ranch research, participatory research
  • Farm Business Management: whole farm planning
  • Pest Management: botanical pesticides
  • Production Systems: integrated crop and livestock systems
  • Soil Management: green manures, soil quality/health


    Fifty-five taro (Colocasia esculenta) cultivars were evaluated for resistance to the root-knot nematode Meloidogyne javanica. All cultivars were hosts, although significant differences in the reproductive success of M. javanica were found within the taro germplasm. Twenty-two green manure species were evaluated in the greenhouse for biomass growth and resistance to M. javanica and taro pathogen Pythium aphanidermatum. Sorghum x sudangrass hybrids (Sorghum × drummondii ‘Sordan 79’ or ‘Graze-all MST’) appeared to be among the best green manure species, because they were very poor hosts to M. javanica, produced copious amounts of biomass, and grew well when inoculated with M. javanica and P. aphanidermatum. In a preliminary field trial, sunn hemp (Crotalaria juncea) was found to be another promising green manure crop, because it fixes nitrogen, has a low-host status for reniform nematodes (Rotylenchulus reniformis), and produces good biomass accumulation. Five field trials were conducted on four islands in Hawaii to evaluate management practices for green manure crops. Overall, initial populations of root-knot nematodes were low and barely at the level of detection in several field trials, particularly on the islands of Molokai and Maui. No significant differences due to green manure treatments were found for subsequent taro yields in two field trials on Molokai and Oahu. In contrast, on Maui, taro grown after nematode-susceptible buckwheat (Fagopyrum esculentum) had smaller corms in comparison with taro grown after nematode non-host sunn hemp. On the island of Hawaii, when root-knot nematodes were present in the soil at the start of the field trial, growth of green manures for 2.5 or 4 months had a beneficial effect on the individual fresh corm weight of the subsequent crop of taro. This beneficial effect could be due to: a) lower initial numbers of root-knot nematodes; b) lower numbers of reniform nematodes; and/or c) to greater exchangeable potassium (K) in both soil and taro leaves, perhaps caused by slow release of nutrients during decomposition of green manure crops. Based on analysis of the soil microbial community, the beneficial effects of green manures probably were not caused by changes in bacterial community diversity or population density. A field day was held on Molokai to demonstrate the growth of various green manure crops and management techniques such as flail mowing of green manures and treatment of vegetative propagating materials of taro to minimize spread of nematodes. A five-minute video showing the highlights of growing green manure crops was produced and is available for viewing at the Sustainable Agriculture Research and Education (SARE) web site of the College of Tropical Agriculture and Human Resources, University of Hawaii.

    Project objectives:

    1. Determine resistance/tolerance of newly introduced taro germplasm against root-knot nematodes.

    2. Evaluate biomass potential of green manure crops, resistance to root-knot nematodes and Pythium, and nematicidal or fungicidal activities of decomposition products.

    3. Determine the best management practices for green manure crops.

    4. Assess the impact of green manure crops on soil bacterial, fungal, and nematode communities in the field.

    5. Conduct effective educational outreach to disseminate project information to taro 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.