A Comparative Study of Low Input and High Input Taro Production in American Pacific with Special Reference to Pest Control

1989 Annual Report for LW89-011

Project Type: Research and Education
Funds awarded in 1989: $258,430.00
Projected End Date: 12/31/1991
Matching Non-Federal Funds: $316,600.00
Region: Western
State: Hawaii
Principal Investigator:
Agnes Vargo
American Samoa Community College

A Comparative Study of Low Input and High Input Taro Production in American Pacific with Special Reference to Pest Control


In the Pacific Islands, taro has always been richly woven into the fabric of life. In 1989 the USDA SARE (formerly called LISA) program funded a study of taro production systems in the American-affiliated Pacific Islands. The primary purpose of the study was to document and test traditional or current methods of crop protection, soil conservation and maintenance of soil fertility. The project surveys, called "Rapid Rural Appraisals" were completed during the first year of the study.

As a result of the surveys, the research teams from each of the islands submitted proposals to perform experiments or conduct ecological studies based on the traditional or modified low-input systems on their islands. Since there are unique circumstances found in each location, studies differ from island to island. This effort will verify the effectiveness of traditional practices in sustaining ever-evolving taro production systems. With a combination of historic indigenous practices and environmentally sensitive technological advancements, the continued expansion of the taro industry in the Pacific will contribute to the economic development and health of these islands.


(1) Document indigenous taro production systems in American Samoa, Yap, Palau, Saipan, Guam and Hawaii with emphasis on identifying sustainable crop production and soil fertility maintenance strategies.

(2) Compare pest and disease damage in taro production in selected low- and high-input farming systems.

(3) Compare economic returns of taro production in selected low-and high-input farming systems.

(4) Disseminate information to agricultural researchers, extension agents, teachers, farmers, government decision-makers and the general public on the advantages and disadvantages of low- and high-input taro farming systems.

Project Results

Objective 1: Documenting indigenous taro production systems:
The following traditional practices are now being encouraged by researchers and extension to achieve soil conservation, fertility maintenance, and crop protection from insects, diseases and weeds in the region.
-Soil Conservation:
Intercropping with fruit and multipurpose trees
Mulching with coconut, pandanus, banana, other leaves
Rows of grasses, shrubs, weeds, and rocks on contours
Cutting weeds instead of pulling
Establishment of terraces
Diversion ditches and berms
Planting on dikes
Tree trunks left when clearing
Triangular planting pattern
Contour planting
No-till with digging sticks
Minimum tillage

-Soil Fertility
Exploitation of different root zones/agroforestry
Rotations and fallows
Interplanting with nitrogen-fixing trees
Green manures
Fish guts, manures
Pasture rotations

-Weed Management
Hand weeding, laying weeds as mulch
Manipulation of water levels in wetlands
Azolla as shade
Cultivar selection for fast initial growth
Increased plant density
Intercropping with fast low-growing plants

-Insect Management
Confusion and barriers with intercrops
Coleus blumei as repellant
Smoking planthoppers
Smashing by hand
Chickens in fields to control armyworms
Soap solution for aphids

-Disease Management
Fallows from one to four years
Increase organic matter
Ash, corral lime and potassium applications
Clean and/or treated planting material
Removal of diseased leaves or plants
Removal of mature plants
Increased spacing
Decrease soil temperatures with mulch or water

Continuing with the survey work done in the first year, the Yap project has detailed descriptions of 12 different taro production systems on Yap alone. Sustainability of some of these systems is being threatened by development of roads and alteration of the hydrology of the island. The documented "Rapid Rural Appraisals" should help influence farmer opinion and concerns about further development on the island.

Objective 2: Compare pest and disease incidence in selected low- and high-input systems:

In Pohnpei a higher incidence of leaf blight and planthoppers were found on low versus high-input farms. Low-input practices were developed indigenously before the introduction of these problems. Farmers have not been able to respond effectively to these new pest and disease challenges due to a lack of knowledge and experience. The result has been a general decline in the abundance of taro and a decrease in the importance of the crop as a food source.

Contrary to previously published information, taro leaf blight was lower in the rainy season on Pohnpei. Recommendations formulated by island farmers to mitigate the problem were:
Use planting material from disease and pest-free plots only and dry storage for the material for two to three weeks to reduce leaf blight infection;
Apply small amounts of complete fertilizer early in the crop to increase vigor, which discourages disease and insect infestation;
Rotate taro with other crops or land fallow between crops;
Discourage overstory (shade) since it may increase incidence of leaf blight; and
Decrease the use of pesticides for planthoppers, which also effects populations of the natural pest manager, the predator, Cyrtorhinus fulvus. This predator has been successful in responding to planthopper outbreaks.

In the Northern Marianas higher inputs of hand labor for weeding resulted in considerably higher yields thatn the current practice or rototilling weeds. This may be due to rototiller damage to the developing taro roots. In Hawaii there was no significant difference in yields from high-input or herbicide treatments and rototilling. However, yields of No. 1 corms were slightly higher in the herbicided plots. In a separate experiment it was found that using a living mulch of Desmodium heterophyllum under the taro did not decrease yields of taro, although the number of suckers produced was lower.

In Guam taro planthoppers were more abundant on fertilized versus unfertilized plots. Feral pigs consumed significantly more plants in weeded than non-weeded plots. No increase in the size of the main corm was achieved by desuckering the plants twice. Late weedings (not a current practice) did increase yield by 870 kg/ha. The predator of taro planthoppers introduced to Guam in the 1950’s does not appear to have survived. In American Samoa results of intercropping Coleus blumei were inconclusive. Use of Erythrina subumbrans (a nitrogen-fixing tree) appears to warrant further study.

Economic Analysis
A comparison between the islands studied showed that the highest rates of return per acre for taro were achieved in Guam, which can be termed a "medium input" system of production. Commercial fertilizers were used in low amounts, weed control was mechanical (no herbicides used), and no pesticides were used, as predators seem to keep pest populations in balance. In contrast, Hawaii’s high-input system of using large amounts of commercial fertilizers, herbicides, and pesticides resulted in a lower rate of return (Guam=$5,873/acre and Hawaii=$3,730/acre). High labor costs and low farm-gate price also impacted Hawaii’s rate of return. In American Samoa, which has a lower fertilizer input than Guam, but a higher herbicide input, yields were lower and therefore rate of return was only $1,927/acre. However, American Samoa does have the highest acreage (1,836) in the region studied, so apparently this level of return is high enough to keep farmers growing taro.

Dissemination of Findings
A conference was held at the end of September, 1992 and a proceedings is in publication. A summary report of the survey, or "Rapid Rural Appraisal," is being reformatted for reprinting. A videotape and extension booklet has been completed and distributed covering traditional and current methods of soil conservation, fertility management, and crop protection. Farmers meetings were held to show the video and discuss project findings on each island where the project was based. A presentation was given and video shown at a Sustainable Agriculture conference in Kona, Hawaii (October 15, 1992) sponsored by the World Sustainable Agriculture Association and the University of Hawaii.

Potential Contributions and Practical Applications
If the findings of this study are adopted, more Pacific Islanders will successfully grow more taro. The social impact will be deeper pride in and understanding of locally-developed methods of taro production and people of the islands will gain a nutritional benefit from eating more taro, which is nutritionally superior to the western diets which taro and other staples are being replaced with. Specific finding show that in some cases low-input traditional methods result in a more stable system and should be maintained. In particular, pesticide use could be reduced and healthy populations of the planthopper parasite encouraged without lowering yields. Traditional practices have successfully prevented soil erosion and, if they are maintained, silting over of bays and reefs will be prevented. Use of mulches as a source of fertilizer as well as a weed suppressant will result in less potential damage to ground and surface water than if farmers apply chemical fertilizers and herbicides.

Evidence from the study of Pohnpei indicates that, contrary to common belief, leaf blight may not necessarily be associated with the rainy season. Low-input strategies that formerly insured a sustainable taro crop are sometimes inadequate when new insects and diseases are introduced from the outside world.