Food and Fertilizer Technology Center - publications

Jul. 01, 1999

Appropriate Pesticide Use, and Testing for Residues

Agricultural chemicals such as fertilizers and pesticides have made an important contribution to Asian agriculture. They have brought about large yield increases, and have helped ensure that the rise in Asia's food production has kept well ahead of its rise in population. However, there is growing concern about the safe use of these chemicals, and the potential dangers to farmers themselves, the environment, and consumers. There is particular concern about pesticides, since almost all chemicals which can kill insect pests are also potentially damaging to human health.

In the last two years, FFTC organized, first a regional survey and then an international seminar, to assess the use of chemical pesticides on Asian farms, and constraints to their safe and effective use. Misuse of pesticides can usually only be detected by laboratory tests. Great efforts have been made to develop the best possible testing procedures, and efforts are continuing.

Another important aspect of appropriate pesticide use is an education and monitoring program, that will inform farmers whether they are using pesticides properly, and will inform consumers whether food is safe. Policy makers also need to have reliable information on the levels of pesticide residues which are present in farm produce. This will enable them to identify problems quickly, and develop programs to solve them.

Accordingly, in 1999 FFTC organized an international training course where information was exchanged on pesticide residue monitoring programs being applied to agricultural products in various Asian and Pacific countries. It also discussed topics such as Integrated Pest Management (IPM), evaluating the safety of pesticides, assessing pesticide exposure, and the best way to train farmers to use pesticides safely. It included hands-on laboratory training on analytical methods to detect chemical residues.

Information Presented at the Training Course

The course opened with eight country reports, which showed how each country operated its residue monitoring program. Each report discussed the registration procedure for pesticides; the establishment of tolerance levels or maximum residue limits (MRLs); how agricultural products are being monitored for residues; and the current status of residue levels being found in food and the environment. Each report also showed what analytical methods are currently being used, and which pesticides are routinely being analyzed. In addition, each country report showed what programs are being followed to assess the risk of particular pesticides when accidentally applied to the skin or inhaled, and programs to educate farmers on the safe use of pesticides.

Industrialized and less industrialized countries had similar lists of banned chemicals, and similar registration procedures for new pesticides. However, the level of monitoring was less in the second group of countries, and the percentage of samples with residues about the permitted limit was generally higher. This was partly because farmers had less knowledge about applying chemicals and less efficient spraying equipment. It is also partly because a really thorough national monitoring system for pesticide residues is expensive, and takes a long time to establish.

The presentation of country reports was followed by a series of eight lectures which discussed general aspects of pesticide use and residue detection. These included pest status information used in practicing IPM; evaluating the impact of pesticides on human beings and animals; establishing tolerance levels for food safety; and multi-residue analysis of fruits and vegetables.

Hands-on laboratory training was an important part of the workshop. The trainees were divided into four groups and trained in various procedures, including field sampling and sample preparation.

Some Recommendations from the Training Course

Impact of Ipm

While it is true that so-called IPM program is an ideal strategy for keeping insect injury below the economic threshold, at present, it remains an ideal concept which is difficult to put into practice. More ecological information on pests, crops, weeds and climate needs to be gathered before IPM can be a really effective way of controlling pests. Farmers will have to depend on chemical measures for at least another decade if we are to maintain the quality and quantity of our food supply. Therefore, it is very important to educate farmers in how to use pesticides safely.


Legally admitted chemicals are not likely to create residue problems if farmers use them properly. Companies which are producing pesticides must provide farmers with information on how to do this. More attention should be paid to the quality of the information on labels. These should be written in local languages if necessary.

Monitoring of Standing Crops

For vegetables and fruits, for which freshness is a vital quality, residue analysis should be carried out on standing crops. This will discourage farmers from bringing suspect produce to market. It will also help farmers to time the harvest of their crops so as to avoid violations.

Residue monitoring program by governments should be based on the analytical results of both the toxicity and quantity of chemicals found to be common contaminants of produce. The percentage of violations in Taiwan is tending to become lower over time. This clearly shows the effectiveness of educating farmers.

Some Important Questions Raised at the Training Course, and Their Answers

What kinds of pesticides create the most serious residue problems in Taiwan?

These differ from crop to crop. Generally speaking, however, cheap generic compounds such as metheamedophose and monocrotophose, as well as some synthetic pyrethroids and some fungicides, tend to be the biggest problem.

In some cases, agricultural produce which violates maximum residue limits is brought to market. Is there a penalty for the farmers responsible? Is the contaminated produce destroyed?

Standing crops or produce on the market containing the residues of banned pesticides are burned. The farmer responsible is penalized (if he can be identified). If standing crops contain residues of registered pesticides over the maximum tolerated limit, the farmer will be informed of the fact and instructed to postpone harvesting his crop until it is safe.

As to the samples collected from markets and found to be violating the law, the only thing governments can do is to confiscate the produce and destroy it. It is very difficult to trace it back to the farmer who shipped it. Harvested vegetables which violate the limits are always destroyed. It is too risky to use them even as animal feed. In the long term, the best way of solving residue problems is to teach farmers how to use pesticides in a safe and responsible manner.

Which Ministry is in charge of investigating pesticide residues on farms or in markets?

The country reports show that the Department (or Ministry) of Agriculture is usually in charge of monitoring residue investigation on farms, for the purpose of educating farmers, supplying safe foods and enforcing the pesticide law. The Department of Health, on the other hand, is in charge of testing produce for sale in markets and enforcing the Food Hygiene Law.

Are all microbial pest control agents safe for the health?

All commercial products are safe, since they must pass safety checks before they are registered. Some agents submitted for registration are rejected, because of doubts about their health effects.


Education of farmers is the quickest way to solve the problem of pesticide residues. Governments, therefore, are recommended to pay more attention to this. Education should be based on reliable data concerning the violation of national pesticide laws.

Legally admitted chemicals are not likely to cause residue problems, provided farmers follow the manufacturer's instructions about when and how to apply the chemical. The label on the bottle or package should give application methods and precautions in clear, simple language which farmers are able to understand.

Index of Images

  • ac1999h1.jpg

    Figure 1 Taking Samples of Vegetables Growing in the Field to Test Them for Pesticides

  • ac1999h2.jpg

    Figure 2 Training Course in Testing Vegetables for Pesticide Residues

Read more

Postharvest Losses of Fruit and Vegetables in Asia
Postharvest Losses of Fruit and Vegetables in Asia
AgriculturalPolicy DragonFruitNetwork