Even though cover crops rarely provide direct cash returns,
they’re rapidly proving their worth as off-season crops for
helping to control insect pests, plant pathogens and weeds.
They also reduce soil erosion, improve soil structure and
nutrients and increase soil organic matter. This project is
intended to demonstrate
the value of sunn hemp as a cover crop in cucumbers. Field
trials of sunn hemp helped determine its impact on soil and its
effectiveness at helping to manage nematodes, insects and
The main cash crop of the farmer producer is cucumber. However, he was suffering a significant loss in marketable yields in this crop due to plant-parasitic nematodes. Additionally, the farmer producer had discontinued growing bitter melon a high value
crop because of continued crop failure. Subsequently, prior to initiation of this project it was determined that plant -parasitic nematodes were responsible for crop failure. The main goal of this project was to teach him and his laborers how to improve the economic viability of their farm by using the cover crop, sunn hemp as part of an integrated pest management system. Our main goals were to demonstrate how sunn hemp could be incorporated into his current production practices to concurrently improve soil health and
nutrient level, and help suppress weed and nematode pests.
1. Determine the impact of sunn hemp on soil and plant nutrient status.
2. Determine the effect of sunn hemp on key nematode, weed, and insect pest populations.
3. Quantify the impact of sunn hemp on vegetable productivity and marketable yields.
4. Encourage Hawaiian growers to produce their own sunn hemp seedsource.
5. Deliver an integrated, sustainable, and economically viable cover crop system to growers and educators.
Our results are being disseminated to vegetable growers beyond the cooperating producer through extension publications, farm site visits, web postings, and extension agents. In the past, Hawaii growers were given limited information regarding the use of cover crops for nematode management and thus mainly relied on nematicides and crop rotation for their management. However, crop rotation is not an option for those farmers with limited land and/or who grow a few crop types, and all or most are susceptible to similar
nematode species. Thus, sunn hemp offers an additional option. However, one of the leading constraints to greater adoption of sunn hemp and other sustainable practices into IPM programs for nematode management in Hawaii was the availability and
dissemination of information. Through our collaborative research and outreach efforts, we have started to disseminate more information to stakeholders on nematode biology and how sunn hemp can be used as a sustainable option for their management .
Since the beginning of the project, some growers have gained a better understanding of nematodes and the mechanisms by which sunn hemp and other cover crops can be used not only to suppress their population but increase soil health through the enhancement of
beneficial soil organisms. We now expect to see a reversal in a dependency on chemical nematicides. Two extension publications have been published and posted at the college website and an additional publication detailing results of the field experiment is being
prepared. Some of the work will also be presented at a symposium during the upcoming Entomological Society of American meeting. We are also refining our field methods to maximize the potential benefits of sunn hemp and increase farm profits.
Educational & Outreach Activities
Hooks, C.R.R, H.-H. Wang, and D. Falon 2006. An ally in the war against nematode pests: using sunn hemp as a cover crop to suppress root-knot nematodes. University of Hawaii at Manoa College of Tropical Agriculture and Human Resources, Plant Disease Publication PD-32. www.cthar.hawaii.edu/oc/freepubs/pdf/PD-32.pdf
Hooks, C.R.R, A. Fereres, and K.-H. Wang. 2007. Using protector plants to guard crops from non-persistent aphid-borne non-persistent viruses. University of Hawaii at Manoa, College of Tropical Agriculture and Human Resources, Insect Pest Publication IP-32. www.cthar.hawaii.edu/oc/freepubs/pdf/IP-32.pdf
McHugh, J. and L. Constatinides. Benefits of cover cropping in agricultural fields – Part 2. Wailua, Oahu, Hawaii. January 9, 2007.
Farm visits and consultations:
Alberta de Jetley LLC., Bennie’s Farm
Harry Ige Farm
Khamphout Farm (Producer cooperator)
Properly identifying crop pests allows for informed decision making regarding how to mitigate their negative impact on crop performance. Prior to the beginning of this project, the producer and his caretakers did not have the ability to recognize plants infected by plant-parasitic nematodes, specifically root-knot nematodes. Thus, field surveys of infected cucumber plants were conducted in coordination with the producers during which he was taught how to recognize galls associated with the presence of root-knot nematodes. Subsequently, we explained to him that applying additional fertilizer would not compensate for stunted plant growth associated with the nematode feeding. Further, at the time, the producer thought his only option for suppressing nematodes was the use of nematicides. The farm workers are Lao immigrants and can’t read English; therefore an extension publication on how sunn hemp can be used to help suppress nematodes was written and translated into their native Lao language. Currently all of the workers on the producer farm are familiar with root-knot nematode damage. This alone resulted in lower production costs because fertilizers are now more judiciously applied. Further, the producer is more confident and knowledge able with regards to nematode management and thus plans to start growing bitter melon again. To reach greater immigrant farm
communities in Hawaii, the publication on using sunn hemp for nematode suppression was translated into three additional languages (i.e., Thai, I1ocano, Cambodia) and handouts of the publication as well as a discussion of our work was presented to participants at a field day entitled "Benefits of cover cropping in agricultural fields".
No studies were previously conducted in Hawaii to determine the impact ofsunn hemp on nematodes, soil health and fertility, and crop plant nutrient levels concurrently. Thus, a field study was initiated in January 2007 at Khamphout Farm on Oahu, Hawaii to determine the effect of sunn hemp on these parameters; and at the request of the producer, it was conducted in a field that had a history of poor yields and crop failure, presumably due to nematodes and other unidentified problems (e.g., soil borne pathogens). A randomized complete block design with four replications of each treatment type was established. The treatment plots were either planted with sunn hemp cover crop
or left as bare-ground. In January, 2007 cucumber were transplanted into bare-ground plots. For sunn hemp plots, alternate sunn hemp rows were strip-tilled using a hand tiller and inter-planted with cucumber. Cucumber harvesting was carried out during the months of March and April 2007. Nematode, plant and soil nutrient samples were collected from all treatment plots during key dates of the experiment. During the study, cucumber plant stands and subsequent yields were recorded. Numbers of melon fly damaged fruits were also recorded from each treatment habitat.
We have started promoting the use of sunn hemp as an alternative to chemical nematicides for nematode control. Farm visits are ongoing to familiarize growers with the use of sunn hemp and other cover crops as part of an integrated disease management program. We have noticed a significant jump in the number of growers interested in using sunn hemp on their farm. We are now in the early stages of evaluating sunn hemp as part of a double cropping strip-till system that includes cucumber and eggplant. Both of these crops are susceptible to root -knot nematodes, and are the specialty crops of Khamphout Farm. The belief is that after the sunn hemp-cucumber intercrop is complete (i.e. cucumber harvest period is complete); the producer can intercrop eggplant into the mature sunn hemp and harvest the seeds from sunn hemp rows during the eggplant growth and harvest period. This strategy will allow growers to continuously produce their own sunn hemp seeds without taking the complete field out of vegetable production.