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The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The views expressed are those of the author. The mention of any product does not constitute its recommendation.
This publication is based on the Manual of fumigation for insect control (FAO Agricultural Studies No. 79, FAO Plant Production and Protection Series No. 20), by H.A.U. Monro, which first appeared in 1961 and was reprinted in 1964. A second edition, revised by the author, was published in 1969 and was reprinted five times.
© FAO 1984
This manual deals with fumigation for the control of insects above the ground. Soil fumigation is not discussed because it is a separate field of endeavour. The manual is written for the practical fumigator and for the official who is required to conduct or supervise fumigation treatments. The book may also be of interest to senior planners and consultants in crop protection who need information on the scope and limitations of fumigation as an instrument for insect control.
Fumigation continues to play a valuable role in many pest control operations; however, both the concepts and the procedures for controlling insects and other organisms are changing. With increased public concern over the adverse effects of pesticidal chemicals on human health and the environment, greater emphasis is being given to methods that can circumvent the use of these materials. Nevertheless, the need for chemical pesticides, particularly the fumigants, is likely to continue for many years to come; fumigants have unique properties and capabilities that permit use in numerous situations where other forms of control are not feasible or practical.
In bringing the subject of fumigation up to date it has been considered important to put some emphasis on the concept of pest management and the integration of pest control procedures. Fumigation should be viewed as just one of a number of techniques that can be used to prevent or control insect infestations. Best results are likely to be obtained through comprehensive management of all aspects of food storage and preservation to give maximum protection against pest infestation.
The present work is based on the manual written by H.A.U. Monro (First Edition, 1961), which gave a comprehensive account of the basic principles and practices of fumigation. Much of this information is still valid and it has been retained, largely in its original form, with new information being added where appropriate and necessary. New chapters have been added to give some information and references on other measures of control closely related to fumigation and to put the subject into perspective with a total pest control programme.
In the preparation of the manual, valuable help and guidance affored by colleagues throughout the world is gratefully acknowledged. In addition, Jonathan Banks, Commonwealth Scientific and Industrial Research Organisation, Canberra, Australia, gave considerable assistance with the chapter on controlled atmosphere storage and Vern Walter, McAllen, Texas, US provided comments on training in fumigation. I am particularly grateful to H.V. Morley, Director of the Research Centre, Agriculture Canada, London, Ontario for valuable support and assistance in the preparation of this revision. The assistance given by the library service of Agriculture Canada and by our librarian, Dorothy Dew, is also gratefully acknowledged. T. Dumas, S.K. Hobbs, G. Lambert, F. Smeltzer and J. Witmer assisted in preparing and checking the manuscript and my daughters Judy and Eleanor provided invaluable help with the typing and final assembly of the manuscript. Photographs marked 'C British Crown Copyright' are reproduced by kind permission of the Slough Laboratory, Ministry of Agriculture, Fisheries and Food, UK.
In modern terminology a fumigant is a chemical which, at a required temperature and pressure, can exist in the gaseous state in sufficient concentration to be lethal to a given pest organism. This definition implies that a fumigant acts as a gas in the strictest sense of the word.
This definition excludes aerosols, which are particulate suspensions of liquids or solids dispersed in air, and which are popularly referred to as smokes, fogs or mists. It is important to make this distinction at the outset because it emphasizes one of the most important and useful properties of fumigants: as gases they diffuse as separate molecules. This enables them to penetrate into the material being fumigated and to diffuse away afterwards. On the other hand, aerosols are unable to penetrate even a short distance into materials because their particles are deposited at the outer surfaces.
Insecticides, which are sprayed on leaves or other surfaces so that insects coming in contact with them or eating them are poisoned, sometimes exert sufficient vapour pressure to give off gas. Under certain circumstances, this gas may account for some of the toxic action - the so-called "fumigation effect". This manual will not deal with this subject; the discussion here is confined to fumigants which are dispensed so that the poison is present as gas soon after application and reaches the insect only in this form.
Present Status of Fumigation
Fumigants are still widely used for the control of insects and other pest organisms. Because of their unique characteristics and the great adaptability of the fumigation technique, fumigants can often provide effective, economical control where other forms of pest control are not feasible. In many cases treatments can be carried out on infested material without disturbing it in any way. The development of lightweight plastic sheets to enclose spaces or materials requiring fumigation has extended the use of fumigants and made control procedures easier and much more adaptable. Several modern technological developments, including instrumentation for gas detection and analysis, improved formulations as well as increased demand for effective and economical pest control measures, have done much to improve fumigation procedures.
Modern technology and research have also brought to light certain problems with fumigants that were previously unknown. Numerous investigations made on both the acute and chronic effects of fumigants have shown that some of these materials are capable of producing serious effects on human health. In some cases fumigants with excessive hazard potential have been restricted or prohibited so that they are no longer widely used for pest control in some countries.
In this edition of the manual, all of the fumigants in the previous editions are included and the nature of hazards posed by any material outlined so that the fumigator will be aware of potential problems. Fumigant use is, more and more, being determined on a risk-benefit basis, where materials with unusual hazards are used only because no effective substitute is available. When such materials are used, the fumigator should take additional precautions to avoid any hazard. Misuse or accidents that generate adverse publicity can do much harm to the practice of fumigation and may jeopardize public acceptance of other fumigants not having such effects. Great care should be taken to ensure that fumigants are always used wisely and carefully.
The practice of pest control is becoming increasingly specialized and requires professional personnel who are familiar, not only with the pest and the pesticide, but who also have a good knowledge of the many factors related to pest infestation and control. Even in field applications, where much of the work may be done by relatively unskilled people working under a well-trained foreman, a working knowledge of the principles of fumigation can be an asset.
In addition, reasonable physical fitness, mental alertness and the ability to understand verbal and written instructions and to carry these out carefully are required. In this field, physical fitness includes absence of any respiratory trouble which might make the operator unduly susceptible to the effects of gases or protective equipment.
Personnel assigned to fumigation work should receive thorough instructions on the properties of fumigants and training in safe methods of handling. This manual can provide the basis for a suitable course in these aspects of the subject.
Scope and Use of the Manual
The manual deals primarily with the use of fumigants as insecticides. This aspect in itself is very broad. The control of bird and mammalian pests is also mentioned in connexion with certain fumigants.
There is no discussion of soil fumigation since this is a complete subject in itself. Because control of nematodes is mainly an aspect of soil fumigation, the effect of fumigants on this group is not considered fully here.
It is not possible, or even desirable, to describe here a large number of treatments in great detail. Instead, in order to make the manual as widely useful as possible, there will be a discussion of basic principles followed by a description of some of the more general applications which can be adapted to deal with specific problems. Emphasis will be placed on those techniques which can be readily employed without the use of elaborate equipment. Expensive equipment, where it exists, is operated by personnel already thoroughly trained in the work. Some recommendations for actual treatments will be given in the various schedules, but these will be representative rather than comprehensive. However, known exceptions and pitfalls will be stressed wherever applicable.
To avoid needless repetition, an attempt has been made to mention most subjects only once. The information required to carry out a certain technique may, therefore, have to be obtained from different chapters. For instance, if a certain fumigant is to be used in a certain type of application described in one chapter, it is essential that the section in Chapter 6 dealing with that fumigant be read to obtain additional information which may be applicable. Also, the section in Chapter 3 on precautions must be regularly consulted until a certain procedure is completely mastered.
Fumigation is just one of a number of methods that can be used for controlling pests in stored products. The best control is likely to be obtained when all appropriate measures are taken to eliminate pest organisms. In an effective pest management programme, methods of prevention and control are integrated to give maximum protection of goods at the lowest possible cost. Other ways that have been found effective in preventing and controlling infestations are as follows:
2. Exclusion of pests.
3. Low temperature - "freeze-outs", refrigeration, aeration.
4. High temperature - heating of mills.
5. Moisture control - grain drying.
6. Aeration - cooling, drying, elimination of temperature gradients.
7. Protectants - chemicals, inert dusts, natural compounds.
8. Residual or contact insecticides.
9. Atmospheric gases - carbon dioxide, nitrogen.
10. Gamma radiation, radio and sonic waves, microwaves, infra-red radiation.
12. Insect growth regulators.
13. Insect pathogens.
15. Insect resistant packaging.
16. Resistant varieties.
An effective integrated pest management system should begin with comprehensive planning to include all aspects of the problem, followed by the application of preventive and control methods. For example, the planning of pest management for a commodity like farm stored grain may be divided into five major categories:
- exclusion of the pest organism;
- inspection procedures;
- good housekeeping and sanitation;
- physical and mechanical control;
- chemical control
Infestation problems can often be reduced by careful planning so that the possibilities of pest organisms reaching the commodity will be kept to a minimum. Location of the storage relative to sources of infestation is important, as well as quality of the structure. Well-built storages, with a minimum of sites where debris can accumulate and insects develop, are desirable. Other features of the storage that should be considered include facilities for conditioning such as aeration systems or driers, provision for proper inspection and cleaning and appropriate facilities for pest control procedures.
Preventive and control methods may include the following:
1. Use of sound structures for storage of commodities.
2. Maintaining clean conditions around storages.
3. Removal of residues of grain or other material from the storage facility four to six weeks prior to storing newly harvested produce.
4. Spraying of storage with approved residual insecticide after removal of food residues.
5. Storage of commodity in a condition suitable for optimum storage, e.g. grain is best stored at low moisture levels.
6. Treatment with appropriate insecticide protect ant at the time of storage may be desirable.
7. Use of aeration or other procedures to cool grain and maintain uniform temperature below those favourable for insect development.
8. Regular inspection to determine
(a) evidence of insect activity
(b) accumulation of moisture
(c) changes in temperature
9. If insects are detected, grain should be fumigated; where field infestation occurs grain should be fumigated within six weeks after harvest.
Fumigants are a unique and particularly valuable group of pesticides that can kill insects where no other form of control is feasible. To a large extent they are irreplaceable. The use of certain fumigants has been restricted in some countries because of suspected adverse effects. Excessive use of fumigants or the misuse of them to cause accidents and produce adverse publicity is likely to bring about even greater restrictions in their use.
By careful planning and management, fumigation may be incorporated into food preservation systems so that fumigants can be used more effectively and safely than when used independently. They should never be used as a substitute for sound management and good sanitation procedures. The benefits derived can include reduced cost of storage with improved food quality, reduced residues in food materials, greater occupational safety and less environmental contamination. All of these benefits are of great concern to the general public and will be factors that have to be taken into consideration in the future use of fumigants.
The ultimate goal in the control of pests in stored products should be to so improve the methods of handling, storing and processing commodities, that the need for pesticides will decrease. Fumigants will then only be needed when unavoidable infestations are encountered.
There are many chemical compounds which are volatile at ordinary temperatures and sufficiently toxic to fall within the defintion of fumigants. In actual practice, however, most gases have been eliminated owing to unfavourable properties, the most important being chemical instability and destructive effects on materials. Damage to materials may take place in several ways, as follows:
1. Excessively corrosive compounds attack shipping containers or spoil the structure and fittings of fumigation chambers or other spaces undergoing treatment.
2. Reactive chemicals form irreversible compounds, which remain as undesirable residues in products. In foodstuffs such reactions may lead to taint or the formation of poisonous residues. Other materials may be rendered unfit by visible staining or by the production of unpleasant odours.
3. Physiologically active compounds may destroy or severely injure growing plants, fruit or vegetables, and may adversely affect seed germination.
Highly flammable compounds are not necessarily excluded if dangers of fire and explosion can be controlled by the addition of other suitable compounds, or if fumigation procedures are carefully designed to eliminate these hazards. Toxicity to human beings is not necessarily a cause for exclusion. All known fumigants are toxic to humans to a greater or lesser degree and ways can be devised for their safe handling under the required conditions of application. However, some commonly used compounds have been shown to be capable of producing long-term effects that were previously unknown. The use of such fumigants is becoming more restricted and some materials have already been eliminated from the list of fumigants approved for use in certain countries.
Table 1 lists a number of common insecticidal fumigants which have been used for many years. Although some of these fumigants may no longer be extensively used they have been included here and in other parts of the manual so that adverse effects as well as useful properties can be indicated.
The final selection of a fumigant for any particular pest control problem will be influenced by the various properties of the compound along with the type of pest organism and the nature of the commodity (Heuser, 1975). As the number of chemicals approved for use as fumigants is small, and is declining, this selection is being narrowed to a very few.
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