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January 2008. A message from NARI (National Agricltural Research Institute), Papua New Guinea: there is a problem with Red flour beetle (Tribolium castaneum) and Rice moth (Coryra cephalonica) damaging maize and peanut seeds stored for planting. How can they be controlled?
Vietnam suggested fumigation with phosphine; it does not effected germination of the seed. Sealing is very important as the gas is toxic to humans and animals. In addition to fumigation, it is important to consider the control of insects in the storage facility. The fumigant has no residual activitiy and re-infestation may occur after treatment of the seeds. Treatment of the storage facility is probably best done using insecticidal sprays.
In Cambodia, a weevil problem in sweet corn was solved by drying the seed well and then storing it in old 4 litre powdered milk tins placed in the freezer for a few days. Freezing kills all the insects, but does not effect germination of the seed, if it is dry enough. The benefit of this method is that there is no risk of exposure to pesticides
Another way is to use neem. Obtain a few kernels or dried leaves of the neem tree (Azadirachta indica) and incorporate them in the storage containers. There is no harm to humans or domestic animals. But since A indica is a large tree which grows mainly in dry climates it may not be in PNG [Editor: it is present]. There is a related species A excelsa which is grown widely in Malaysia for timber, and seeds of this are equally effective. Check if this tree is present in PNG. Extensive studies on the efficacy of neem are reported in H Schmutterer’s book The Neem Tree. It is IMPORTANT that you do NOT use Indian beed tree, Persian lilac, Chinaberry (Melia azedarach) which is poisonous to humans.
The suggested rates for neem are: neem seed kernels 2 to 4% w/w of grain; and dried pulverised neem leaves at a higher rate (about 5% or so).
For neem, the kernals are removed from the seed capsule and then ground before mixing with the grain. Alternatively, as seed powder can inpart an odd smell to the grains, it can be put in small cloth bags inside the storage bins with the same result.
Note that Persian lilac is under test in Papua New Guinea as a mulch for the control of sweet potato weevil). Four to six sprayings of 2% Persian lilac aqueous extracts have been used in Cuba and reportedly reduced populations of C formicarius. But be careful it is toxic to humans.
In place of neem, Annona squamosa can be used.
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