General Information on Phosphine Fumigation
Phosphine gas moves readily through grain from the point of application. Phosphine leaks quickly through holes in silos or sheeting. Wind and large temperature changes accelerate phosphine loss. Most phosphine is lost within four days from fumigations in ordinary, unsealed storages. Insects are killed slowly by phosphine gas. The fumigant must be kept in contact with the insects for at least 7 days to kill all stages of the insect´s life cycle that usually exist in stored grains. Fumigation in ordinary, unsealed storages will kill some adults but most eggs, larvae and pupae will survive to continue the breeding cycle. A silo that is built to be sealed gas-tight is needed to contain sufficient phosphine concentration for long enough to kill all stages of the insects. Fumigation gives no residual protection to stored grain. In other words, insects will begin breeding, after the phosphine gas concentration has dropped to low levels. Phosphine fumigant itself leaves minimal residues, and is acceptable to most markets. However, the solid powdery residues left by phosphine generating tablets when they are mixed with the grain are a concern to some markets. It is against label recommendations to mix solid phosphine generating tablets directly into the grain. Phosphine is effective against insects in most types of grain. But some commodities (for example, oilseeds – linseed, cottonseed) soak up phosphine very quickly, leaving little to kill insects.