Surinder Sud: Nature to the rescue

FARM VIEW

The sugar industry in Maharashtra is in dire straits. It is unsure of getting adequate supply of cane this year. Many plants run the risk of closure because of the paucity of cane. The erratic and inadequate monsoon rainfall is a cause for the decreasing acreage under cane crop.

But that's not the only reason. Equally responsible is a pest called woolly aphid. Its population, and the consequential crop damage, has risen so much in recent years that many cane growers have switched over to cultivating other crops.

The problem is not confined to Maharashtra alone. In neighbouring Karnataka as well as several other sugar-producing states, cane cultivation is in jeopardy because of this growing menace.

However, cane growers and the sugar industry may not have to despair for long. A cost-effective and environment-friendly way to combat this menace has been found by scientists at the Indian Council of Agricultural Research (ICAR).

Significantly, the new method does not depend on pesticides to kill the pest. It deploys a natural enemy (insect predator) of the woolly aphids to kill them.

Experts at the Lucknow-based Indian Institute of Sugarcane Research (IISR), led by G M Tripathi and R B Jadhav, have discovered that an insect called Dipha (Dipha aphidivora) has a natural instinct to eat up woolly aphids. In its larval stage (the initial stage of the life cycle), Dipha is a voracious feeder and has the ability to devour the pest population under conducive conditions.

Of course, there are other natural enemies of woolly aphid as well, such as Micromus igorotus, spiders and some others. But the trials conducted by IISR scientists using Dipha in Maharashtra and Karnataka have given them enough confidence to recommend this as a bio-remedy for the problem.

In fact, some of the sugar factories located at Kolhapur, Sangli, Satara, Pune and Ahmednagar also cooperated with the scientists in trying out this method of biological pest control with good deal of success.

Woolly aphid (Ceratovacuna lanigera) is essentially a sucking pest found in about 20 countries. But it has been known as a major sugarcane pest only in some Asian countries, notably the Philippines, Indonesia, Taiwan, China, Japan, Korea and Pakistan.

In India, woolly aphid has until recently been classified as only a "minor pest" of sugarcane, confined mainly to Nagaland, Assam, Tripura, Sikkim and, to some extent, West Bengal.

The first major epidemic of woolly aphid on sugarcane was noticed in July 2002 in Sangli district of Maharashtra. It soon spread to other areas, including Kolhapur, Satara and Pune districts of Maharashtra and Belgaum in Karnataka.

It played havoc with sugarcane crops that are grown in different seasons "" adsali crop, pre-seasonal crop, suru crop and rattoon (perennial) crop. And almost all the popularly grown sugarcane varieties succumbed to it.

The fight against this pest has been a rather tough one because of the peculiar nature and life cycle of this insect. The larvae (nymphs) of this insect move fast and within hours settle on the lower surface of cane leaves. Soon the nymphs and the adults cover almost the whole surface of the leave, sucking the sap and rendering it dry.

Simultaneous, they keep excreting a sticking substance called honey dew that covers the upper surface of the leaves and serves as a convenient host on which the fungus can develop. The leaves start wearing a sooty look and become incapable of photosynthesis.

This causes loss of yield as well as sucrose content of canes. The leaves become unfit even for feeding to cattle. Worse still, under favourable circumstances, the adult insects develop wings and travel to other areas to disseminate the scourge to newer areas.

Several pesticides have been tried to control this pest, but they have failed to provide total protection. Besides, these have to be sprayed so many times that the farmers find the costs prohibitive.

The breakthrough in finding a cure for the pest came when, during a survey of woolly aphid-infected fields in Kolhapur and Satara districts, IISR scientists discovered the presence of some Dipha insects and observed them killing the woolly aphid.

They collected Dipha nymphs from these fields and bred them in the institute's biological control centre to increase their numbers. These were then released in the cane fields to take on the woolly aphid and keep the pest population under check without incurring heavy costs.

It is, indeed, now for the sugar industry, as also for the state agricultural departments, to organise multiplication of Dipha and other known predators of woolly aphid for releasing in cane-growing areas to revive sugarcane cultivation in the country's major sugar belts.