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June 14, 2007

Optimal pesticide use can save cotton farmers

by Neena Bhandari

A relatively low-tech approach to managing pesticides promises to help hundreds of thousands of cotton farmers across Asia raise yields and reduce environmental contamination. Scientists are collaborating with groups across Asia to combat the cotton bollworm (Helicoverpa armigera), a major pest that causes five billion US dollars worth of crop damage each year and serious distress to farmers in countries like India.

The bollworm is prevalent in 29 cotton producing countries across Asia, Australia, Africa and Southern Europe. Besides cotton, this moth attacks more than 100 different commercial crops including maize, wheat, sorghum, sunflower, chickpea, lupins, soybeans, tobacco, tomato, lettuce, sweet corn, capsicum and beans and flowers including chrysanthemums, gladioli and roses.

Derek Russell and Philip Batterham, professors at the 'Bio21 Institute' of Australia's University of Melbourne have been working closely with Keshav Kranthi of the Central Institute of Cotton Research in Nagpur (India) and a number of other groups in India, China and Pakistan, to develop technologies to aid farmers in their fight against this destructive moth.

About 40 percent of the annual cost of growing cotton is spent on insecticides by the eight million cotton farmers spread across 11 states in India, while still failing to control the caterpillars. Cotton bollworm has often caused total crop loss, driving hundreds of Indian farmers to suicide. According to official figures maintained by the provincial government of Maharashtra, close to 1,500 farmers, most cotton growers, committed suicide in 2006 and the trend has continued this year in spite of attempts at intervention by the government.

Besides making the pest resistant, indiscriminate spraying of insecticides has created ecological havoc. Russell says, "By the mid 1990s, Indian cotton farmers were spending 43 percent of the variable costs of cotton production on insecticides, around 80 percent of that being for cotton bollworm control. Insecticide use on cotton was 50 percent of all insecticide use in the country and it was increasing at seven percent per annum. For many, perhaps even most, cotton production was being rendered uneconomic."

"In 1998-99, 14.6 percent of Indian cotton production was lost to insect - mainly cotton bollworm - damage. The Green Revolution had increased the area of more susceptible cotton bollworm hosts and the intensification of cropping patterns meant that these hosts were available all year round." he adds.

Kranthi and his collaborators have implemented a control programme in thousands of Indian villages, slashing insecticide use by 50 percent, which has led to increase in yields by 11 percent and profitability by 75 percent. In the Wardha district of central Maharashtra, where the programme was introduced in 1997, common insecticides once again kill cotton bollworms easily.
Apart from higher yields, selective use of insecticides has major benefits for the environment and human health. A 2004 survey found that under the programme the number of farmers poisoned by insecticides had decreased roughly tenfold.

Russell says, "There were seven major groups of insecticides being used. Now farmers are using four groups and rotating them intelligently, keeping human and environmental health in mind." The strategy is implemented in an integrated pest management context, avoiding the use of insecticides that kill the bollworms' biological control agents or disrupting control of other pest species in the cotton. The group has had some major successes, recently identifying resistance genes for two important classes of insecticides, the neonicotinoids and the spinosyns.

The collaborators have developed a number of test kits, similar to home pregnancy test kits, which allow the farmer to determine if an insecticide will be effective against the moth. It is now possible to test the quality or identity of the insecticide, thereby allowing a farmer to check whether he is getting what he paid for. Another test detects whether a population of moth will be affected by a particular insecticide.

As farmers' spraying habits tend to be heavily influenced by their neighbours, the scheme is introduced to whole villages at a time. The programme tells farmers how to check whether insecticides are needed and if so which type of insecticide to use and when best to use it, so that during each of the four month-long "windows" of the growing season, only one type of insecticide is used. The life cycle of the Helicoverpa armigera is about one month, so the offspring of any resistant insects that survive one round of insecticide are killed by a different one the next month.

Some aspects of the programme have been introduced in China and Pakistan. In Uganda, they have taken a different approach says Russell. "There is no effective agricultural extension support structure in Uganda, so, with donor and national collaborator support we have been running 9,000 demonstrations per year. By the end of 2007 we would have contacted every cotton grower in Uganda."

A similar test has been developed by Kranthi to check the integrity of Bt cotton - a transgenic form of cotton that contains a bacterial insecticide. Seeds can be ground up and a dip-stick style test used to detect the presence of the toxin. Undoubtedly, Bt cotton has been a huge success with widespread adoption in a number of countries including Australia, China, India and the U.S, but public opposition to the genetic modification of food crops means that in the short-term genetically modified Bt plants are not a viable alternative for controlling the moth on the majority of the crop species it attacks.

The next crucial step is to sequence the moth's genome, to find its Achilles heel.

"We believe it will be possible in the future to manage or prevent resistance so that farmers can keep their produce in the market. To maximise control over insect pests, we are working towards next generation solutions - pest-specific insecticides," Batterham adds.


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