Pesticides used in rice cultivation are having just the reverse effect than the one intended -instead of decimating pests, extensive studies reveal that they are, in fact, destroying precisely …

-- (Credit: Urvashi Narain / cse)INDIA'S Green Revolution in the'60s had a baneful side to it too- the use of high-yielding seed varieties led to a spurt in fertiliser and pesticide application. This was especially true of rice, the staple food of a majority of Indians and other Asian people. The continent accounts for over 90 per cent of the worlds rice production. But Asia's warm and humid climate, the intensive use of fertilisers, and the practice of multiple cropping created conditions favourable for pest growth. Also, the high-yielding rice varieties being promoted were susceptible to pests. The pests became a menace and the scientific community's only answer to the problem was to encourage farmers to use more pesticides.

But far from being an answer to the pest menace facing rice farmers, pesticides are today becoming a part of the problem. Scientist, who in the '60s had promoted pesticides, are now asking farmers to reduce pesticide use. Besides adversely affecting the health of the farmers, pesticides can kill the natural enemies of the pests, instead of the pests, and thereby cause, rather than prevent, a pest outbreak. Having finally recognised the drawbacks of pesticides, several Asian nations are implementing integrated pest management (IPM) programmes to reduce pesticide use in rice, the region's largest crop.

More than 100 species of insects attack the rice crop, but most of the damage is caused by 3 pests - brown planthoppers, stemborers and leafhoppers. Even though plant breeders have developed several varieties that are resistant to the major rice pests, farmers have not decreased pesticide use. There are 2 main reasons for continued high pesticide use: varietal resistance has not lasted - for example, in 1977, in Indonesia the resistance Of IR26 to brown planthopper broke down in 3 months - and often a given variety is resistant to few but not all rice pests.
Pestilential response Paradoxically, in many South and Southeast Asian countries, the increased application of pesticides has been accompanied by an outbreak of the brown planthopper (Nilaparvata lugens)- the most harmful of the 3 major rice pests. In 1977, Indonesia lost over a million tonnes of rice to the planthopper. Again, in 1986, despite the introduction of rice varieties resistant to the brown planthopper and the heavy use of pesticides, about 200,000 ha of rice fields were infested by the pest. Thailand had the largest brown planthopper outbreak in its history in 1989-90, with over 400,000 ha being affected. Similarly, in Malaysia the area infested by the planthopper increased to over 9,000 ha in 1990, from less than 500 ha in 1989.

Says Peter Kenmore, the regional programme coordinator for Food and Agricultural Organisation's (FAO) integrated pest control programme in rice in South and Southeast Asia, "Nearly every recorded outbreak of the planthopper in the tropics has been associated with use of insecticides."

A study conducted by the International Rice Research Institute (IRRI) at Los Banos in the Philippines has shown that of the 39 commonly used insecticides by the Filipino farmers can cause brown planthopper resurgence.

In order to understand how the excessive use of pesticides can cause pest outbreaks, one has to understand the ecology of the rice field.

Every rice field has an abundance of insects but only some of these are pests. A majority of the other insects are predators and parasites that target rice pests, thereby keeping the pest population under control. Pesticides can potentially disrupt the natural control process by killing the natural enemies, not the pests, and thereby permitting the pests to multiply unchallenged. This argument presumes that the natural enemies of rice pest are more vulnerable to pesticides than the pests, a fact that is borne out in the case of the brown planthopper.

The brown planthopper has 3 predators, each of which attacks the pest at a different stage of its development. The plant bug Cyrtorlhinus lividipennis) feeds on the planthopper eggs, devouring up to 200 eggs a day; the water strider bugs (Microvelia douglasi atrolineata) kill newly hatched brown planthoppers and wolf spiders (Lycosa pseudoannulata) concentrate on older planthoppers, consuming upto 45 adults every day.

So what goes wrong? Explains K L Heong, entomologist and coordinator of the IPM programme at IRRI, "The brown planthopper eggs are embedded in the stem of the rice plant and, therefore, are protected against pesticides, unlike their predators', the plant bug." Similarly, adult planthoppers are protected by a hard abdomen unlike their predators - spiders, who have soft abdomens and are, therefore, easily wiped out by pesticides. Besides, when the plant canopy becomes thick, which is after about 45 days, penetration of pesticides is difficult and they become less effective. Heong draws an analogy between the use of pesticides against the brown planthopper larvae and the use of bombs by the Americans against the Vietnamese soldiers. Like the Vietnamese soldiers safe in underground tunnels, the pests hide inside the protective cover and are unharmed by the pesticides.

The disruption of the natural balance between the pests and its enemies can also accelerate the process by which the resistance of rice varieties to major pests is broken. Biological variations among the pests permit some strains of the pests to feed on a pest-resistant variety. Without pesticides, natural enemies are able to control the population of pests that can feed on the resistant variety. But with the natural enemies killed, as happens when pesticides are used, the pesticide-resistant strains can multiply unchecked and ravage the crop.

Besides playing havoc with the paddy ecosystem, pesticides can adversely affect the health of rice farmers and those who spray pesticides. The use and unsafe handling of hazardous pesticides can lead to pesticide poisoning while prolonged exposure to pesticides can produce ' chronic ailments such as cardiopulmonary, neurological and skin disorders .

In the Philippines, of the 4,031 acute pesticide poisoning reported by the Department of Health hospitals between .1980 and 1987, 603 proved fatal. Says IRRI agricultural economist P L Pingali, "The number of poisoning is likely to be underestimated, since most Ases do not reach the hospital, and rural health officers may not always correctly diagnose pesticide poisoning."

According to Heong, farmers tend to overuse pesticide because they are unable to differentiate between pests and friendly insects. A study of pest management practice of 45 farmers from the province of Laguna, conducted by IRRR and the University of the Philippines at Los Banos (UPLB) found that 31 per cent farmers thought that all insects were enemies of rice. Only a few farmers were able to identift spiders, dragonflies, and grasshoppers as natural enemies of rice pests. Most farmers (80 per cent) resorted to pesticides when they saw "any" type of insect because they believed that could damage the rice plant.

Sometimes even when farmers are able to differentiate between pests and predators they overuse pesticides because they overestimate the damage caused by a particular pest. The rice leaffolder (Cnaphalocrocis medinalis) is one such pest. Farmers believe that the rice leaffolder causes substantial yield reductions by feeding on the leaves of young rice plants. However, research at IRW has shown that it takes as many as 15 rice leaffolders per rice plant to affect the yield and the pest population rarely grows to that level. In fact, the rice plant can compensate for any early leaf damage by these insects by later growth.

Standing up to a pests
Resistance of a few International Rice Research Institute (IRRI) varieties to inspect pests
Variety Year of release Brown planthopper Yellow September leafhopper
IR5 1967 Susceptible Susceptible Susceptible
IR26 1973 Resistant Susceptible Susceptible
IR36 1976 Resistant Mildly resistant Susceptible
IR64 1985 Resistant Susceptible No data available
IR74 1988 Resistant Mildly resistant No data available

Sick on pesticide
Hypothesised health effects of chronic exposour to pesticides
System Effects Symptoms
Eye Pterygium Vascular membrane on eye
Skin Eczema Lichenification and fissuring
  Nail destruction


Respiratory Bronchial asthma Wheezing cough
Cardiovascular High blood pressure


Gastrointenstinal tract Chronic gastrities Nausea and vomiting
Kidneys Urinary abnormalities Creatinine

Heong also blames the pesticide companies for encouraging overuse of the chemicals. "Pesticide sales representatives brainwash farmers into believing that unless they spray their field frequently and at the first sight of any pest, they face a great risk of losing their crop," says Heong. Travelling through rural Philippines one comes across more advertisements for pesticides than any other commodity.

Despite the adverse effects of pesticide over use, most governments are reluctant to implement IPM, which relies on alternative pest control methods to reduce dependence on harmful chemicals (see box: Nature's guerrilla tactics). Of all the South and Southeast Asian countries facing the pesticide threat in rice, Indonesia alone has taken concrete policy measures to eradicate the menace. In 1986, the Indonesian government banned 57 of the 63-trade formulations of insecticides used on rice and eliminated 85 per cent of insecticide subsidy. The funds thus saved were used, with assistance from FAO, to organise farmers field schools to improve their pest management practices and thereby reduce the use of pesticides.

So far, 300,000 Indonesian farmers have graduated from farmers field schools. A FAO study reveals that at the farm level the number of insecticide applications per field has decreased from over 4 per season to 0.8 per season. Rice production has infested by more than 12 per cent while formulated pesticide peoduction has decreased by more than 50 per cent. The area infested by brown planthopper has decreased from 200,000 ha in 1986 to about 15,000 ha in 1990.

The success of the Indonesian IPM programme can be judged by the fact that it has survived a major pest outbreak. In 1990, the white stemborer infested 13,000 ha of rice fields in West Java. Despite desperate calls from the villages for a massive distribution of banned pesticides, local governments stuck by the integrated pest management programme. That summer, field trainers rallied 300,000 people to pick the stemborer s pinhead-sized white eggs off the rice plants. In 1991, less than 1,000 ha were damaged by the stemborer. Furthermore, FAO scientists maintain that the rice fields most damaged by the stemborers were in areas where the farmers had panicked and used insecticides.

But other countries have been slow to respond to IPM. Says Kenmore, "It has taken the FAO 11 years to convince the Indian government to implement an IPM programme." As a first step, in 1993, then government eliminated pesticide subsidies and imposed a 10 per cent across the board excise tax on pesticides. However, the bulk of the pesticide subsidy, given by the state governments, remains because these governments lack the courage to implement a policy that at first seems A unpopular with the farmers. This year FAO is helping the Indian government organise farmers field schools across the country. Similar efforts are now-being made in Vietnam, Malaysia, Thailand, Sri Lanka and Bangladesh.

Poison's end
So far the argument has implied that farmers need to reduce pesticide use in rice cultivation. But can farmers do without pesticides altogether? The scientific community is clearly divided on this question. Scientists at the IRRI say no and refer to a 1981 study that had shown that in the Philippines, the average yield from plots protected with insecticides was about 2 tonnes higher per ha as compared to unprotected plots. Heong adds that "although pesticide use is unnecessary in the first 30 days, it may be needed later depending on the severity of the pest infestation".

However, there are those like Jose R Medina, director of the National Crop Protection Centre, in the Philippines who believe that pesticidefree rice farming is not only feasible but lucrative too. "It is a matter of giving the predator population time to catch up with the pests," says Nicanor Perlas, a Filipino farmer, who is an ardent advocate of pesticide-free farming. Their contention is in part supported by the experience of Sesinando Masajo, a Filipino farmer, who has successfully -free farming for the last 12 years (see practiced insecticide box: Pitting nature against pests).

But what if the farmers are faced with a major pest out-break, say, a locust infestation? Should the farmers wait for the natural enemy population to catch up or should they use pesticides? The recent outbreak of locusts in 3 provinces of northern Philippines, in the aftermath of the eruption of Mt Pinatubo, has opened up this controversy.

Officials at the department of agriculture believe that the locust can only be controlled by using a "combination" of natural and chemical controls. Consequently, the department has bought huge quantities of chemical pesticides and has organised power sprayers while it is also advising farmers to bait the locusts with rice hull laced with salt or molasses and to collect the locusts for food. However, Masajo believes that the problem can be solved by simply reintroducing the natural enemies of the locust to the affected areas. There is no one answer.

In conclusion, it is clear that after being promoters of pesticides, scientists and policy makers are today questioning the efficacy of chemical pesticides. However, it is still a matter of debate whether pesticides should be used rationally or done away with completely. Hopefully, the scientific community will reach a consensus soon.

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