DANGERS OF HERBICIDE MISUSE

With the increasing substitution of herbicides for manual labor in weed control, rice farmers need guidance on how to use chemicals, says Keith Moody, weed scientist and acting

head of the Agronomy, Physiology and Agroecology Division of the International Rice Research Institute (IRRI). "It becomes mind-boggling when you consider the huge number of chemicals they have to choose from," he said.

"In Central Luzon in the Philippines alone, 24 herbicides or herbicide combinations are being used byfarmers in wet seeded rice."

Herbicides with properly designed labels warn farmers to wear protective clothing and avoid skin and eye contact with chemicals. Yet Moody told of seeing a Malaysian farmer using a mist blower to apply one of the most dangerous of these chemicals (paraquat), thus allowing himself and others to be exposed to the spray. Paraquat is banned or its use is restricted in some countries.

Another farmer mixed herbicide with fertilizer and insecticide and applied the combination with a mist blower. Still others mixed herbicide with soil and broadcast it on the fields by hand.

On another occasion, Moody saw a farmer who was having trouble with his sprayer put the nozzle in his mouth to blow out an obstruction. Then he held the plunger uip above his face, where it could drip on his skin or eyes, to see if there were other problems.

Keith Moody says that, in many instances, there's nothing wrong with the use of herbicides, it's the misuse that's the problem.

How do farmers treat herbicide poisoning? "In the Muda area of Malaysia", says Moody, "the majority of people drink coconut water. I've had farmers say to me, 'Unless I feel sick, the compound won't do its work.'

The increasing use of herbicides also poses the problem of weeds developing resistance to them.

"It's not a matter of if weed resistance will occur, it's a matter of when it will occur," said Moody. "It's going to come, and in fact it has already occurred. In Malaysia, they have weeds resistant to 2,4-D and in China, to butachlor. In the Philippines, butachlor is widely used in rotation with pretilachlor, both of which have the same mode of action. Therefore the likelihood of herbicide resistance occurring in the Philippines is quite high.

"This is of concern," he said. "I think people need to take a close look at these compounds and make some hard decisions as to whether a single compound should be applied. I don't think they should. Mixtures of herbicides having different modes of action should be used."

An IRRI study shows that 24 percent of groundwater samples in the Philippines were contaminated with low levels of butachlor, said Moody. "Low levels don't remain low for long. I believe that this compound has been withdrawn recently from the market in Japan. This may have implications for other rice-growing countries throughout the word."

As water becomes scarce in Asia, the demand for herbicides will increase, Dr. Moody said, because they are cheap and there appears to be no alternative. I can pay for the most expensive herbicide in rice in the Philippines with the proceeds of the sale of 100 kilograms of rice," he said. "If you get a 4-ton yield, that's 2.5 percent of the cost of the crop. Handweeding is 5-10 times more expensive.

In addition to the need for increased farmer education about herbicide use, new products are needed that cause fewer environmental pollution will make herbicides increasingly unacceptable.

(IRRI news release)