Control recommendations for LGB and other storage pests require farmers to dry and shell their maize, utilize appropriate and improved storage structures, and, to apply a dilute dust formulation directly to the grain before storage. Currently, the dust formulation recommended for use contains pirimiphos-methyl and permethrin, but any suitably registered and compatible organophosphorous plus synthetic pyrethroid insecticides could conceivably be used.
Dilute dust admixture has the advantages of low cost, simplicity and safety for the small-scale farmers, compared with other storage pest control measures. The problem in the past has been instability and consequently, short shelf life of many commercial dust formulations. This largely resulted from the use of unsuitable materials as diluents (fillers). The problem previously concerned malathion, hut it could be anticipated that newer insecticides or mixtures will face similar problems because, like malathion, they maybe incompatible with some of the cheaper, most readily available fillers.
It must he clearly recognised that higher standards of stability are generally required. In developing countries, the products can take longer to ship and deliver to the farmer, they are very likely to arrive too late in the season and have to be stored until the following year, and the climate is generally hotter. A two-year shelf life must he the minimum requirement. Pressure must come from both local and international regulatory authorities to ensure formulators analyse their products and guarantee content and shelf life. These needs have to be supported by national regulations, frequent government analyses and lawful action taken against unsuitable suppliers. The consequences of supplying poor quality dusts are loss of credibility of extension services when control failures become apparent; reversion to use of more toxic, chemically stable and perhaps unregistered dusts; outright rejection of the dusting technique; and potential development of resistance due to survival by under dosing. Suitable dust formulations may be more expensive hut they may nevertheless be more cost effective. Dusts should have a guaranteed shelf life and be date stamped. Making a stable dust is largely a question of choosing the right diluent and adding a sufficient overage to compensate for loss of insecticidal content over time. If, after proper investigation, a stable dust formulations cannot be locally produced, the product should not be registered and available on the market.
In Tanzania, ready.-to-use dust formulations of actellic super dust were imported to control LGB. More recently, the active ingredients have been imported, and the dusts formulated locally utilizing either finely divided coconut husk or cassava flour, as the diluent. It must be noted that farmers are quite perceptive; if they have become accustomed to a particular product and they are confident it works, any change (for example, the colour) may cause them to be suspicious and not use it, even if the change is beneficial. Extension services play a pivotal role in ensuring this sort of information is disseminated throughout rural communities. Finally, it is important that ready-to-use dust formulations are provided in plastic sachets, date-stamped, and in sizes that are compatible with the volume of farm-stored maize to be treated. Standardization to 100g sachets of actellic super dust capable of treating one 90 kg sack of maize, obviated many of the earlier problems associated with supplying permethrin (0.5%) dust in 25 kg sacks. This required subdividing into smaller lots for use by the individual farmer in Western Tanzania (GOLOB, 1988) which was achieved using locally available volumetric measures (a clean margarine can; or match box). The sort of problems associated with lack of attention to the farmers needs when selling ready-to-use dusts in this manner, are:
· Farmers will not buy any, because the smallest quantity available is too expensive;· Farmers will not buy any because they lack storage containers for dust excess to their immediate requirements;
· Farmers will not buy if there are not written (understandable) instructions on how to use the dust;
· If farmers do buy, there is the possibility of widespread over-or under-dosing, in the absence of written instructions;
· Farmers will not know what to do with the excess; some will over-dose, some will store it in inappropriate containers and probably under-dose in future treatments, or some will simply discard the excess.
These problem areas and farmers needs must he addressed in any future control programme for LGB. Countries that may be presently free of the pest, hut where the risks of its introduction are high, should already be aware of the reasons why LGB was such a devastating storage pest in Tanzania during the early stages of its introduction. Above all, they should he prepared to support their farming community through the availability of suitably packaged dust formulations when and where it is needed and clear instructions on how to use it properly.
· Farmers will not buy any because they lack storage containers for dust excess to their immediate requirements;· Farmers will not buy if there are not written (understandable) instructions on how to use the dust;
· If farmers do buy, there is the possibility of widespread over-or under-dosing, in the absence of written instructions;
· Farmers will not know what to do with the excess; some will over-dose, some will store it in inappropriate containers and probably under-dose in future treatments, or some will simply discard the excess.
These problem areas and farmers needs must be addressed in any future control programme for LGB. Countries that may be presently free of the pest, hut where the risks of its introduction are high, should already he aware of the reasons why LGB was such a devastating storage pest in Tanzania during the early stages of its introduction. Above all, they should he prepared to support their farming community through the availability of suitably packaged dust formulations when and where it is needed and clear instructions on how to use it properly.
