Which fumigants to use?

Generally, two types of fumigants are available for fumigation purposes in grain storage programme.

a) Methyl bromide: It has a quick action and the grains can be aerated after 12-24 hours of its application. However, it is highly toxic, colourless and odourless, has residual effect in the grain and accumulates in the human body. For this reason, methyl bromide should not be used as a fumigant in grain storage programme.

b) Magnesium or Aluminium phosphide : Gas released from this chemical is known as Phosphine. This fumigant has a small molecular weight (34.04) and thereby has excellent penetration capacity. The weight of phosphine gas is similar to that of air, so it easily gets mixed with air and spreads all along the stored grains. This eliminates the need to have re-circulating fans to circulate the air. This is very effective against most pests but does affect taste or smell of the fumigated grain. At the same time, it leaves no residues on the grain, so it can safely be used for food grains.

Moreover it does not affect the germinability of seeds and therefore, can safely be used for storage of seeds also. However, it is inflammable at normal temperature, so proper care should be taken at the time of its application. This has a delayed release and, therefore, requires longer period of fumigation than other fumigants.

Depending on weather methyl bromide or phosphine is used, the duration of fumigation should be 24–48 hours for methyl bromide, or a minimum of five days for phosphine. The latter product is more commonly used, since its application, in the form of pellets spread throughout the grain mass, is simpler. It is essential to recognize, however, that fumigants are very poisonous to people and therefore the staff that is to use them must be carefully trained in their application. For all these treatments, it is important to scrupulously observe the recommended protective and safety measures (masks, gloves, hand-washing, hermetic sealing of phosphine containers, etc.).