Post green-revolution, pest problem assumes different hues

The pesticide umbrella that helped in increasing food grain production, when the green revolution began to unfold its socio-economic benefits, has now begun to leak.

It is causing wide spread damage to the environment, making agro-ecosystem vulnerable to a new host of pests and insects and causing pesticide-residue effects in a variety of food stuffs and even human milk.

Consequently, Punjab Agricultural University (PAU) has to deal with a slew of new problems. The insects and pests have developed resistance to many plant protection chemicals.

Scientists have encountered the problem of resurgence of new pests, of pesticide-residues, outbreak of secondary pests and toxicity to natural enemies. Since agriculture is now in the cusp of change, so is the control of new pests and insects with new technologies.

Excessive use of pesticides or misuse of pesticides has caused pesticide-residue problem in all sorts of agricultural commodities and including human milk in the state. Entomologists at PAU say that approximately 55 per cent of food commodities in Punjab were found to be contaminated with pesticide-residues in 1997-2004.

The percentage of contamination in cereals due to use of DDT, HCH was observed to be eight per cent and six per cent, respectively, and percentage contamination due to DDT and Lindane in milk was two and 53, respectively. Pesticide residues were also found in vegetables. Various pesticides were reportedly responsible for contamination of up to 71 per cent in vegetables and 85 per cent in fruits.

Since major emphasis in the initial years had remained on increasing food grain production to meet the country's needs, the use of pesticides also increased from 2,353 million tones in 1955-56 to 41,020 million tones in 2003-04. The percentage share of pesticide consumption in Punjab was 17.9 in 2002-03. This decreased from 7,200 metric tones in 1995-96 to 6,900 metric tones in 2004-05.

According to entomologist A K Dhawan, a new "chemistry" is in the offing to overcome problems posed by old insects and pests. This chemistry relates to application of smaller doses of pesticides that are cost-effective and have long-term effect.

Even spray technology is different, as the new pesticides have different "modes of action" on pests or killing these pests in ways different than the traditional pesticides. These "novel pesticides" have been registered for control of "sucking" pests and also for American bollworm and pink bollworm.

Today, with the adoption of Integrated Pest Management practices, insecticide usage has been reduced by 55 per cent on cotton crop, cutting the cost of sprays by 38 per cent. The presence of BT cotton is likely to cause a dip of 70 per cent in pesticide consumption in the Malwa belt. Similarly, in sugarcane, with the adoption of bio-control strategies, pest incidence was reduced by 60 per cent and pesticide use by 90 per cent.

Dhawan said even in vegetables several pests have developed multiple resistance to nearly all commonly used insecticides.

"We have regularly recorded several pests on a variety of plants and crops. For instance, armyworm has emerged as a pest of wheat, maize and sorghum. Stalk-borer is a new pest in sugarcane. Also, a new species of 'weevil' and 'toka' are serious pests of wheat in rain-fed areas. However, as more area comes under assured irrigation, aphid will become a major problem."