Yams are in Decline, Herbicides Can Help


yam (left); sweet potato (right)

The dominant zone for yam production in the world is in West Africa, where about 93% of the world’s production occurs. Yam is a major source of calories for millions of people. Yam produces the highest amount of food calories and protein annually per hectare. Currently, yam farming is very labor-intensive and the crop is in decline.

“Weeds pose an increasingly serious challenge in yam cultivation. Speargrass is a noxious rhizomatous perennial weed found especially in the lowland sub-humid zones of West and Central Africa where it severely constrains crop production. …Chemical control reduces speargrass density leading to higher yields.

As far back as 1982 several authors, as summarized by Diehl… predicted a future decline in yam production based on economic and agronomic considerations. The major issues were shortage of labor, in view of the labor intensive nature of yam cultivation… limited availability of seed yams; declining soil fertility associated with reduced fallow periods; and a reported shift in demand to cheaper commodities in some areas.

More recently a mathematical model, based on FAO data, predicted that yam production could decrease dramatically over the next 15 years. They attributed the predicted decline to a combination of high costs of production, inadequate yields, losses in storage and unfavorable prices to farmers.

The cost of labor in yam cultivation (about 40% of total variable cost) is high and increasing. Yam farmers are ageing and have increasing difficulty in coping with the challenges of cultivation. Increasing urbanization is leading to increased labor shortage and cost. Yam production systems will benefit from:

…increased use of mechanization and other labor-saving practices (e.g. use of herbicides).”

Authors: Asiedu, R., and A. Sartie.
Affiliation: International Institute of Tropical Agriculture, Nigeria.
Title: Crops that feed the world 1. yams.
Source: Food Security. 2010. 2:305-315.


40 Million People Protected from Blindness Thanks to Insecticides

Naked Africans Walking

Children leading blind adults in Africa

Onchocerciasis, also known as river blindness and Robles disease, is caused by infection with the parasitic worm Onchocerca volvulus. Symptoms include severe itching, bumps under the skin, and blindness.

The parasite worm is spread by the bites of a black fly of the Simulium type. Usually many bites are required before infection occurs. These flies live near rivers therefore the name of the disease. Once inside a person the worms create larva that make their way out to the skin.

“The control of onchocerciasis, or river blindness, in West Africa has been hailed worldwide as a public health and economic development success. The World Health Organization (WHO) and the World Bank estimate that because of The Onchocerciasis Control Programme (OCP) in West Africa 40 million people have been protected from river blindness and an estimated 600,000 cases of blindness have been prevented in the 11 participating countries, 25 million hectares of arable land in previously infected river valleys have been open to resettlement and cultivation, and food resources for an estimated 17 million people are now being produced.

OCP achieved its success by controlling the vector of this disease, a Simulium black fly that transmits the disease-causing filarial worm, through application of insecticides to vast stretches of rivers (>50,000km at the peak of control activities) spread over large geographical areas (1,235,000 km2). Applications were frequent (near-weekly during 10-12 months each year) and, in some cases, lasted for 20 years.”

Authors: Resh, V. H., et al.
Affiliation: Department of Environmental Science, University of California, Berkeley.
Title: Long-Term, Large-Scale Biomonitoring of the Unknown: Assessing the Effects of Insecticides to Control River Blindness (Onchocerciasis) in West Africa.
Source: Annu. Rev. Entomol. 2004. 49:115-139.

African Cocoa Farmers Need to Increase Fungicide Use

Black Pod

Black Pod

70% of the world’s supply of cocoa, a key crop for producing chocolate, comes from small farms in West Africa. In this hot, moist tropical environment, cocoa trees flourish but so do organisms that infect the cocoa pods causing diseases-particularly black pod disease. Fungicides are used to a limited extent by West African farmers, but they are not sprayed often enough to prevent the disease organisms from causing significant damage. As a result, African cocoa yields and farmer incomes are low. Research has shown that for optimal yields and income, West African cocoa farmers need to spray fungicides more frequently as a recent economic analysis determined…..

“Essentially fungicides were not overused – in most cases, it was shown that net returns could be increased by using more fungicide in the study area. Specifically farmers in Osun State would have to double their current use rate to optimize fungicide use while their counterparts in Ondo State would have to triple theirs to achieve the same goal.

Based on the results of this study, it is suggested that cocoa farmers increase the quantity of fungicide used per hectare as the ratio of the marginal productivity to unit cost of fungicide is greater than unity among the respondents.”

Author: A.A. Tijani
Affiliation: Department of Agricultural Economics, Obafemi Awolowo University, Nigeria
Title: Economic benefits of fungicide use among cocoa farmers in Osun and Ondo states of Nigeria
Source: J. Soc. Sci., 12(1):63-70 (2006)