Pick Those Podborers

Pod borer larvae, in the genus Helicoverpa, can decimate a pigeon pea crop. However, an indigenous practice that was abandoned in the past in favor of chemical treatments is once again being used. We read about it in the December 2000 issue of Spore and also on ICRISAT’s web site (www.icrisat.org). The technique is surprisingly simple. Pigeon pea plants are shaken gently so that the pod borer larvae fall off. As the larvae fall, they are collected on a sheet that is pulled along the ground between the rows of plants. A few hens follow and eat the protein-rich larvae.

The use of chemicals to treat the larvae increased gradually throughout the 1970s and 1980s, but by 1993, 100% chemical control was used in India for pod borers. Three to six sprays were done per season. When the insects began to build up resistance and spraying was no longer very effective, local people started using the traditional method again.

The technique was obviously effective, but researchers at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) decided to find out just how effective and economical it really was. The technique is more laborious than using chemicals; three people work at once, one pulling the sheet between the rows and the others shaking the plants on either side. In India where the trials were done, three people could cover 0.4 ha in a day. Yet even so, the technique was cheaper than chemical control. Shaking the plants (which required seven people) cost Rs 280/ha. Chemical treatment, including labor, cost Rs 500-700/ha.

In ICRISAT’s tests, plants were shaken at 160 days after sowing, when there were an average of seven larvae per plant. Shaking resulted in an 85% reduction in insect populations, which was better control than with chemical sprays. Whether or not a technology is being adopted says much about its value. This particular shaking technique was used at a few locations in 1997. Within two years, more than 100 villages used the technique. Several thousand farmers in three states of southern India were using the method. The report we read stated that all of those farmers continue with the method. Additional benefits of the technique are the lack of chemical residues and the fact that natural predators (birds, for example) are likely to settle in the area.