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close this bookCERES No. 111 (FAO Ceres, 1986, 50 p.)
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View the documentDisease, pest ravages portray dark side of green revolution

Disease, pest ravages portray dark side of green revolution

Few green revolution success stories read better than that of India's Punjab. Only 20 years ago, the tall-standing local rice varieties yielded an average of one ton of grain per hectare and were impossible to cultivate across large areas of the state. All that changed, however, with the introduction in 1966 of T(N)1, a semi-dwarf, high yielding rice variety from Taiwan, followed two years later by the legendary IR-8, the first of many new varieties perfected in the laboratories of the International Rice Research Institute (IRRI) in the Philippines. Accompanied by "appropriate technology packages" dictating everything from land preparation procedures to the use of fertilizers and insecticides, the semi dwarf varieties produced an unprecedented boom for Punjab rice farmers. By 1983, the area under rice had more than quadrupled, average yields had tripled, and total production had risen from less than 300 000 tons a year in 1965 to more than 4 million. Now, however, farmers have discovered a dark side to the green revolution. Along with exponential growth in production, they have witnessed a dramatic increase in the range and intensity of insect and disease attacks on their crops. At last count, the new varieties were affected by 40 insect pests and a dozen diseases, many of them serious enough to cause appreciable economic losses.

"It's not an unusual case," explains Tran Van Dat, a rice agronomist at FAO. "Experience has shown that the introduction of high-yielding varieties produces marked changes in the pest and disease complex after a certain period of time. That is one reason why IRRI is constantly having to produce new, improved strains." The so-called second generation insect and disease problems affecting rice fields in Punjab have been documented in detail by a three-person research team at Punjab Agricultural University. Before the semi-dwarf varieties were imported, rice plants were affected by only five insect pests and three diseases, the team reported in the June 1985 issue of FAO's International Rice Commission Newsletter. Now, "several insect pests which were hitherto considered as minor have started appearing in serious proportions". In fact, the year after T(N)1 was first planted, leaf-folding caterpillars ravaged crops in one district and have since spread to all rice-growing regions of the state. In 1983, ear-cutting caterpillars caused serious damage in several places. Tiny whitebacked planthoppers and brown planthoppers have reached plague proportions in several districts (destroying more than half the crop in one case), and in 1983 an epidemic of the even tinier rice thrip "caused panic among farmers". Minor diseases have become major ones. Brown spot has spread from submountainous tracts to all of Punjab's rice-growing areas, while another fungal disease, false smut, has been spreading since 1975. In addition, the research team reported, several new insect and disease problems are reducing the new varieties' celebrated high yields. Rice fields now host hordes of cereal leaf flea beetles, horned caterpillars, yellow hairy caterpillars, small brown planthoppers, and sugar-cane pyrilla. "Even termites have been noticed occasionally causing minor damage in fields of paddy crop lacking standing water," the team noted.

What has caused these "second-generation" plagues? The research team explained: "The fields planted to modern varieties develop a distinctly different micro-climate.... The cultivation of dwarf varieties, therefore, seems to have brought relative changes in the status of insect pests and diseases." This is confirmed by the fact that several new pests appeared immediately after new varieties were introduced. Unwise farming practices are also to blame for increasing pest and disease problems. Many farmers have planted high-quality varieties not recommended for their areas, with consequent increased attacks by brown planthoppers, whitebacked planthoppers, sheath blight, sheath rot, and false smut. Other farmers, wishing to free their fields for wheat and Potato crops, begin sowing and transplanting rice too early in the season, which exposes the plants to bacterial blight.

Farmers also made the mistake of putting too much faith in PR-106, a rice variety introduced in 1976, when it was considered resistant to the voracious whitebacked planthoppers. As farmers switched to the new variety, the insects adapted. Today about 80 per cent of Punjab's rice fields carry PR-106 - along with large numbers of voracious whitebacked planthoppers. Finally, many farmers use too much fertilizer, producing large, succulent plants that are more susceptible to insect attack than those grown at lower nutritional levels. "Recent surveys have revealed that more than 50 per cent of farmers in Punjab apply more than the recommended dosage of nitrogenous fertilizers," the rice researchers reported. "In addition, farmers use green manure crops and farmyard manure.... Such an increased use of nitrogen has led to severe infestations and attack by various insect pests and diseases," including rice hispa, leaf folder, planthopper, stem borer, stem rot, and bacterial blight. Interestingly, the overuse of insecticides, which can lead to the resurgence of insect species as they develop tolerance, was not considered a factor in the pest problem. In fact, the use of insecticides and fungicides in Punjab is described as "minimal".

The challenge now is to turn back the rising tide of pests and disease in the rice fields. Several measures are recommended: first, new varieties should be thoroughly tested before release and incorporate resistance to major diseases and insects. Farmers should broaden the genetic base of their crops by diversifying away from PR-106; they should also reduce cultivation of unrecommended varieties, cut back on nitrogen applications, and plant according to recommended timetables. Outbreaks could also be prevented by the setting up of monitoring and surveillance programmes to identify the presence of pests or disease before they become serious. Finally, extreme care should be taken in the future as the use of insecticides increases. "Insect pest and disease problems should be handled through integrated management to avoid further worsening of the situation," the Indian research team said. "Sound pest management systems which integrate varietal resistance with other control measures such as judicious use of insecticides, biological control agents and cultural practices should be developed."

Graeme Thomas