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ols insect and mite pests, andprevents mold growth. This residue-free control technique, applicable in gas-tight rigidstructures and exible enclosures, needs technical expertise to carry out the treatmentand is relatively costly when compared with conventional fumigations. The controlled atmospheres applied may be of either low-oxygen (0.5% oxygen and 9.5% nitrogen) or high-carbon dioxide atmosphere (4% carbon dioxide, balance air) or burner gas(0.5% oxygen, 1% carbon dioxide, balance mainly nitrogen). The choice between the three depends on local availability of the gases, suitability of the structures, and afford- ability. The required gases for producing the controlled atmospheres may be supplied fromindustrial or off-site sources, on it may also be generated on-site (4,. The technique of controlled atmosphere storage of grain is well advanced over the past 2 years mainly in the industrialized countries. Leaky storage structures and subse- quent costs are the major constraints for the adoption of the technique in other countries.Nevertheless, the application of technique is likely to expand in the near future owing tofactors such as development of insect resistance to conventional fumigants, and contactinsecticides and residue problems. Moreover, the system is considered as organic andis exempt from residues (. 4.2 Chemical Methods 4.2.1 FumigantsFumigants are chemicals available as gases, liquids, and in solid formulations, but act on the insect and other pests in gaseous state. Fumigation plays key role in grain preserva- tion as it controls insects developing inside and outside the grain and crawling and hidden pests. Unlike spray treatments with contact insecticides, fumigation is curative treatmentwith no lingering or residual effect. Fumigated stacks or bulk grains are readily reinfested,if not protected properly, or in the absence of an effective prophylaxis. Another advantagewith fumigants is that they can be applied in different types of storage si