3.4.1. Supplementary treatment on surfaces of bags, storage structures, and transport:
3.4.2. Admixture of maize with grain protectant insecticide
3.4.3. General safety in use of insecticides
3.4.1.1. Summary:
LGB is not equally susceptible to all the insecticides which are approved for use in grain stores and on grain. The commonly used group of organophosphorus insecticides (e.g. malathion, fenitrothion, pirimiphos methyl) are less effective against LGB than are the synthetic pyrethroids (permethrin, deltamethrin, fenvalerate, phenothrin, etc). It is therefore important, where there is a specific requirement to control LGB using insecticide, that a synthetic pyrethroid is used. Where there is need to control LGB along with other storage insects then a mixture of an organophosphorus insecticide and a synthetic pyrethroid is required. Suitable combinations may be available commercially in some countries. Alternatively, an appropriate mixture may be formulated locally, observing both manufacturer's guidance on compatibility and suitability, and national regulations restricting the use of only approved and registered pesticides on grain. For spray applications to surfaces of bag stacks and storages, dilution with water according to the manufacturer's recommendations should be made. Spraying may be done using either a pneumatic, an hydraulic hand-held sprayer, a motorised knapsack sprayer, or a pumping unit with spray lines. It is recommended that the outside of the bagged stack(s) must be sprayed before sheeting and, after sheeting for fumigation, the base of the fumigation sheet must also be sprayed. This is a precaution against subsequent reinfestation of the stack. Spraying will reduce the likelihood of any LGB or other storage pests surviving the fumigation by remaining hidden in the folds of the sheet during fumigation, whilst also providing further protection against reinfestation once the fumigation sheet has been removed. It is also recommended that all trucks and wagons used for transporting maize must first be cleaned to remove grain residues and then sprayed with an appropriate, approved insecticide. The serious risk to fumigated stocks awaiting despatch by insects migrating from infested grain residues kept nearby, is to be avoided.
3.4.1.2. Store preparation: (Refer Section 3.1)
· Warehouses must be completely disinfested before the intake of stocks.· The buildings should be thoroughly cleaned and brushed out, and all loose material in cracks and crevices and behind girders, doors and railings should be removed.
· The warehouse should be brought to a good state of repair, and a regular programme of storage inspection and sanitation maintained. To reduce insect and rodent infestations rodent plates on doors and bird netting on ventilators should he fitted or repaired, if necessary.
3.4.1.3. Choice of insecticide:
The effectiveness of a particular insecticide will depend on the surface to be treated, the nature of the pest, the speed of action of the insecticide and whether the insecticide is short lived or persistent. Many organophosphade insecticides may break down within less than one week on some concrete surfaces and may have very short persistence on rough wood or fibre hoard. However, the effect may last much longer than the actual persistence of the residue because of the time it will take for the infestation to become re-established. On smooth surfaces, such as plywood, metal, or paintwork, insecticides may persist for several months.
For the specific control of LGB (and Rhyzopertha dominica, the "lesser grain borer", a very closely related bostrichid beetle pest of stored cereals), and other stored products pests likely to be encountered, structural and bag surface treatments must employ a combination including an approved and registered synthetic pyrethroid insecticide. The organophosphorus insecticides are more active against the non-bostrichid storage pests, such as Tribolium castaneum, Sitophilus spp., Oryzaephilus spp. and Cryptolestes sp., whilst the pyrethroids are more active and persistent against LGB. Using this combination enables broad spectrum control and protection at least cost, by minimizing applied dosages, as well as contributing to maintain residues below established Maximum Residue Limits (MRL's)¹. Synergized natural pyrethrum is also effective against LGB, and maybe considered as a replacement for the synthetic pyrethroid component of the spray combination, in situations where it is more locally available, and longer term persistence not being sought (ie., intransit or short term storage)2.
1 Pyrethroids usually consist of several isomers. In general the cis-isomers are more toxic to mammals than the trans, and it is therefore important to know the isomeric composition of each product; the cis: trans ratio of the insecticide should be kept as low as possible, without decreasing its efficacy. The hazards associated with significant deviations from established ratios should he estimated from acute toxicity studies, and manufacturers should provide such data whenever a pyrethroid is produced with altered isomeric ratios.2 Pyrethrum is mainly used as a space spray and gives rapid knockdown of flies or months It may be applied as an admixture treatment and is effective against bruchids on pulses and against Rhyzopertha dominica on grain. However, it is less effective than the organophosphates against
3.4.1.4. Formulations to be used:
The choice of pesticide formulation depends largely on the nature of the surface to he sprayed. Three formulations are available for mixing with water; the emulsifiable concentrate (ec) and the water dispersible powder (wdp), also called wettable powder (wp), and the suspension (or flowable) concentrate. For porous surfaces a suspension of wettable powder is better, but on non-porous surfaces, such as metal or paintwork, an emulsion may be less effective but is generally more convenient to use and is less conspicuous once it has dried. Emulsions are preferred on cardboard boxes. For treating a store by fogging or misting, oil solutions are used. Parts of the store may also be treated by dusting. (Refer TDS # 17)
3.4.1.4.1 Emulsifiable concentrates (ec):
This formulation consists of insecticides, emulsifiers, stabilizers and solvent oils. The concentration of insecticide varies from 2 to 80 percent of the formulation. Dilution with water produces a stable emulsion in which very small oil droplets containing the insecticide are dispersed throughout the water. Some emulsifiable concentrates can also be diluted with oil (miscible concentrates), Emulsifiable concentrates may be used both for surface applications and for grain treatment.
Sitophilus and Tribolium spp. on grain. Pyrethrum is rapidly broken down by sunlight and, therefore, is not used as a residual spray on walls. Pyrethrum is usually formulated with a synergist (Piperonyl butoxide) at a 1:2, 1:5 or 1:10 ratio. This increases the potency and reduces the dosage needed by blocking the insect detoxification mechanism. The most suitable ratio of synergist to pyrethrum depends on the insect to be controlled.The principal formulation is a 0.3% pyrethrins, 3.0% piperonyl butoxide solution in odourless kerosene or technical white oil for fogging or misting. Other formulations include dusts, aerosols and sprays.
3.4.1.4.2. Water dispersible (wettable) powders:
The formulation consists of a mineral powder impregnated with a high concentration of the insecticide, 25 to 80 percent active ingredient, plus emulsifying agents and stabilizers. Dilution with water produces an even, uniform suspension, but the powder slowly settles out and needs to be reagitated continuously or, at least, intermittently. The use of wettable powders is generally recommended for spraying on absorbent surfaces, such as concrete and unpainted wood, brick or fibreboard, while the use of emulsifiable concentrates is recommended for smooth surfaces. In fact, wettable powders may be much more effective on most surfaces. This appears to be particularly true for the synthetic. pyrethroid insecticides. However some disadvantages of wettable powders are that they are more difficult to apply evenly, harder on spraying machinery and give a more visible deposit than emulsifiable concentrates.
3.4.1.4.3. Oil solutions:
These are solutions of insecticide in mineral oil, which may be either concentrates requiring dilution or dilute ready-to spray formulations. Most foggers and mechanical aerosol generators use oil solutions.
3.4.1.4.4. Insecticide dusts: (Refer TDS # 17)
Insecticide dusts may be sprinkled around stacks or in corners or putted into crevices or between bags. Dusts are more easily picked up by insects than sprays and have a long active life. They can applied by sprinkling or by a hand-operated or motorized knapsa duster. For application to bags, only approved insecticide dusts may he used. Dusts usually contain 1 to 5 percent of insecticide active ingredient and should be applied to give the same application rate of insecticide as recommended for sprays.
Figure 3.6 Motorized knapsack sprayer
3.4.1.5. Concentrations to use:
The manufacturers' recommended application rates given on the formulation label should ALWAYS he consulted. The dilution rates given are generally within a range of 0.5% to 2%, and selection of the lower or higher concentrations may depend upon several factors such as the type of surface, whether a knapsack or a motorised sprayer is used, what particular pests are present, and the time/duration of residual effectiveness that is being sought. In hot humid tropical environments, persistence may be so short on some surfaces, that control may only he achieved by the initial knockdown effects on exposed insects, and confers little, or only very short-term residual protection.
3.4.1.6. Rates of application:
For water-based sprays the dosage rate is normally 5 litres/100m2 (1 gallon/1000 ft2). For adequate cover of very porous surfaces, rates of 10 or even 20 litres/100m2 may be necessary. To avoid excessive run-off on metal, paintwork, etc., the application rate may be reduced to 2.5 litre/100m². This low volume rate is also appropriate for commodities in polypropylene hags. It should be emphasized that the amount of active ingredient (a.i.) deposited must remain the same whatever surface is being treated. It is only the volume of diluent (water) that is varied.
The volume applied will also depend on the type of sprayer being used. The aim is to attain complete coverage without excess run- off, and it may sometimes be useful to determine the optimum rate needed to achieve this by a preliminary practice spraying.
3.4.1.7. What machine to use:
A 4.5 litre (one gallon) pressurized knapsack hand operated sprayer is adequate for small stores, but the 2-18 litre hydraulic type sprayer which must be pumped continuously is often more convenient. For large installations a motorised knapsack sprayer with a capacity of 10 litres is preferable. Spray teams applying large quantities of spray may find a tractor, or vehicle-mounted sprayer with multiple extension hoses and lances most suitable.
3.4.1.7.1. Pneumatic knapsack sprayers:
These are generally of 5- to 15-litre capacity. After adding the spray liquid sprayer is pressurized, by a hand pump, enough to complete discharge of the contents. The sprayer should he fitted with a safety valve and a pressure regulating valve. The output of these sprayers varies from 1 l/min down to 300 ml/min when a size 000 fan jet (for emulsions) is fitted.
3.4.1.7.2. Hydraulic knapsack sprayers:
These are generally up to 20-litre capacity, with outputs up to 2.5 l/min, hut probably generally about 0.3 to 1 l/min, depending on the nozzle fitted. The diaphragm pumps are suitable for all suspensions and extension telescopic lances may extend up to 5 metres. The sprayers should be fitted with pressure regulating valves for even spraying.
3.4.1.7.3. Nozzles:
Hand-operated knapsack sprayers should be fitted with fan spray jets, although a swirl nozzle of similar output can he used. The nozzle should have an output rate of 0.85 l/min at a pressure of 2.1 kg/cm2 (30 psi). When spraying wettable powders, the filter behind the nozzle should be removed. When applying suspensions, the most suitable ceramic fan jet is size 0 and for emulsions size 000 should be used. This reduces the output at 2.1 kg/cm2 (30 psi) to
280 ml/min.
3.4.1.7.4. Motorized knapsack sprayers:
Motorized knapsack sprayers commonly have a 3 hp engine and a capacity of about 10 litres of spray liquid. The output may be up to 3 l/min, hut this is reduced when the nozzle is raised. The vertical throw is 6 to 8 metres. The sprayers weigh about 12 kg and are worn on the back. The operator has to take care to avoid being burnt when lifting the hot sprayer off the back after use.
3.4.1.7.5. Portable spraying pumps:
Portable spraying pumps usually have a 3 to 5 hp petrol engine, although they can also be obtained with electric motors, and for convenience and mobility they are usually mounted on a trolley. The output may he 10 to 30 l/min. There may be an integral tank or sunction lines may be run to a convenient tank, such as a 200 litre drum.
3.4.1.8. Mixing the spray fluid:
For the greatest accuracy the quantity of concentrate should be made up to the required total of 5 litres of spray fluid and not added to 5 litres of water. Only clean, cold water, free from any foreign particles should be used for diluting insecticide concentrates. All mixing containers and spray tanks should also he clean since contamination of spray with other chemicals may lead to rapid breakdown of the insecticide or taint of foodstuffs receiving the treatment. A solvent-resistant, waterproof apron and gauntlet gloves must he worn when insecticide concentrates are handled. Any splashes on the skin must be washed off immediately. Water dispersible powders must be thoroughly mixed in a small quantity of water to a creamy consistency before the remainder of the water is added. The powder will not disperse easily if added directly to the total volume of water used for dilution.
Water dispersible powders vary considerably in the rate at which the powder settles to the bottom of the container. Some settling will begin from the moment that stirring ceases. Consequently, these suspensions must be used immediately after mixing and the sprayer should he shaken at intervals during the spraying to ensure even dispersion of the powder throughout the spray fluid unless the sprayer is fitted with constant agitation device. The mixed spray should he poured into the sprayer through a funnel containing a filter mesh. This will reduce spillage during filling and prevent nozzle blockage during spraying.
3.4.1.9. Spraying procedure:
3.4.1.9.1. Prior notice of the spraying will have been given to warehouse staff whose work is likely to be disrupted and appropriate cleaning measures will have been completed.
3.4.1.9.2. Care should he taken to ensure that all screw threads or unions are tight and free from leakage and that liquid does not seep over the clothing of the operator.
Suitable protection clothing should he worn.
3.4.1.9.3. Diluted wettable powders should be used immediately after preparation, and the sprayer must be shaken at intervals during the spraying to endure even distribution of the powder throughout the spray fluid and to prevent settling out. The shaking of the sprayer may not he necessary if it is fitted with a constant agitation device.
3.4.1.9.4. The area to be sprayed (including wall surfaces, floor, accessible roof, stacks of commodities) will have been calculated and provision of sufficient insecticide, water and sprayers ensured. Protective clothing, washing water and soap should be provided.
3.4.1.9.5. Clear instructions as to the parts of the store to be treated will be given and an estimate of the area to be covered with one tankful of spray will be given to spray men.
3.4.1.9.6. Special instructions should he given to apply heavier- than-normal dosages of spray to known insect harbourages (cracks and crevices in walls, rough wooden panelling, holes, etc.). Hazards such as electrical equipment, dimly lit areas, slippery floors, steep stairways and low roof beams should be known to spraymen.
3.4.1.9.7. When using hand sprayers the nozzle should be held about 30cm from the surface to he sprayed and it should be moved at about 60cm per second to give the desired deposit. Successive vertical bands of spray should overlap slightly. Additional lengths of hose and extension tubes may be fitted to hand sprayers so that the sprayman's reach may be extended.
3.4.1.9.8. Motorized knapsack sprayers must also be correctly maintained. Particular attention should be paid to ensuring that the air filter and sparking plug are regularly cleaned and that only clean petrol and oil mixed in the correct proportions are used for the engine.
3.4.1.9.9. On completion of spraying the petrol supply should be switched off and the engine allowed to run until the carburettor is empty. If this is not done the carburettor may become clogged with oil. When spraying with a motorized knapsack sprayer care should be taken not to use more revolutions per minute (r.p.m.) of the engine than are required to distribute the spray on surfaces. High engine speeds produce excessive airflow which causes spray bounce and will contaminate the sprayman. In the still air conditions within a store, it is practicable to treat roofs and wall up to 6m high.
3.4.1.9.10. Care should he taken to avoid over balancing when climbing on bagged stacks or up ladders in order to treat high places.
3.4.1.10. After treatment:
Immediately spraying is completed a check should be made that all areas have been treated (they will be damp) and that the correct amount of spray has been applied. Any surplus spray remaining in the sprayers may he applied to walls to use it up. The sprayers should be emptied and washed through with clean water. Nozzles should he dismantled and cleaned hut not 'in no case blown through' by mouth. Spray tanks, hoses and lances should he drained and dried. Diluted water-based sprays should not be retained in the sprayer for longer than one day since the insecticide may deteriorate rapidly. Empty insecticide containers should be disposed of safely and party-used containers securely closed. All insecticide concentrates should be kept under lock and key and apart from foodstuffs. Finally, a later visit should be made to confirm that the treatment has been effective and that insects are not surviving in isolated places.
3.4.1.11. Spray application to transport conveyances:
For spraying transportation (railway wagons, trucks and tarpaulin covers) a spray mixture of pirimiphos-methyl and permethrin, or other suitably available and nationally approved organosphosphate and synthetic pyrethroid insecticides (chlorophyrifos-methyl, fenitrothion; fenvalerate, deltamethrin) can be used.
To minimise the risk of shipments becoming infested intransit by LGB, certain pest control operations should he initiated:
· All rail wagons and road trucks to be used to convey maize to countries of consignment should be sprayed with insecticide prior to loading.· All tarpaulins used to cover the loaded wagons and trucks should be sprayed with insecticide.
· All pallets and dunnage used in the stores should he sprayed with insecticide, prior to stacking.
· Stacks should be sprayed and fumigated if stored in excess of tour weeks or if an infestation becomes evident, whichever occurs first.
The following dosage rates for structural treatments can he used:-
Spraying: 250 ml pirimiphos methyl and permethrin 50% active ingredient (a.i.) emulsifiable concentrate plus 20 ml permethrin 5% (a.i) emulsifiable concentrate diluted to 10 litres with water, to treat 200 m2 of surface area.
These dosage rates produce a deposit containing 1 g active ingredient (a.i.) of pirimiphos-methyl, and 80 mg active ingredient (a.i.) of permethrin per m2 of treated surface.
When grain is stored in bulk the admixture of a suitable insecticide may he the most effective means of providing control of insect pests.
A range of insecticides are approved internationally for admixture with grain but, before they can he considered, local registration requirements must be met. Treatment of export grain should only be done after an assurance has been obtained that such grain will be accepted in the receiving country. Appropriately labelled formulations for grain protection are required. An organophosphorus insecticide such as pirimiphos-methyl, chlorphyrifos methyl, methacrifos, fenitrothion or malathion is normally used to control the complex of storage insects other than LGB and other bostrichid beetles. If the infestation includes LGB. the addition of a synthetic pyrethroid is essential. Suitable synthetic pyrethroids include permethrin, deltamethrin, fenvalerate, and phenothrin. The application rate given on the label must be observed; this normally is not more than 10 mg/kg of organophosphorus insecticide and 2 mg/kg or less of synthetic pyrethroid.
3.4.2.1. On-farm storage;
One of the recommendations for farmers is that they shell their maize before storage. This practice facilitates the application of insecticide dusts, and diminishes the potential damage as a result of LGB attack. Laboratory work (Howard, 1983) and field trials and observations (Golob et al., 1985) have clearly demonstrated that LGB develops more successfully on maize stored as cobs than when stored as loose grain. However, storing grain predisposes towards infestation by Sitophilus species which does not normally pose problems when maize is stored on the cob. In order to negate the problems of Sitophilus species, an insecticide dust containing both permethrin and pirimiphos-methyl has bee made available to farmers.
The original insecticide dust used by farmers contained 0.5% permethrin as the active ingredient which applied at the recommended rate of 50 g/90 kg of maize provided a nominal dosage of 2.8 mg/kg. The dust currently available contains 0.3% permethrin and 1.6% pirimiphos-methyl and when applied at 100 g/90 kg of grain produces 3.3 mg/kg permethrin and 17.7 mg/kg pirimiphos-methyl. These dosages provide initial nominal residues which are in excess of the levels recommended by the FAO/WHO Joint Meeting on Pesticide Residues which are, for raw cereals, 2 mg/kg for permethrin and 10 mg/kg for pirimiphos-methyl. (So much active ingredient is lost during application and subsequent decay during storage, however, that these levels do not present a hazard at the time of consumption).
If deltamethrin is used instead of permethrin, it not only controls LGB but, unlike permethrin, it also controls other storage pests including Sitophilus zeamais. Thus, this compound can he used as a general storage insecticide and in Togo it is available as a 0.05% dilute dust for use by farmers. It has not been used in Tanzania, because it cannot he readily formulated locally.
In Kenya spray application of pirimiphos-methyl have been used comprehensively for control. These applications were undertaken in an area where the outbreak of LGB was restricted to a few hundred farmers. In Tanzania, in similar areas of localized infestations, spraying has also been undertaken in conjunction with insecticide dust application in attempts to entirely eliminate the pest from those areas.
It has been estimated that treatment costs for using dilute insecticidal dust formulations of actellic super dust in on-farm storage, are approximately 5% of the value of a 100 kg hag of maize.
3.4.2.2. Large-scale hulk and bagged storage:
When silo bins and bulk warehouses cannot be made gas tight, fumigation is difficult and the admixture of a suitable residual insecticide may be the most effective means of control. The insecticide can be evenly distributed and measured exactly to correlate with the amount of grain needing treatment. Unlike application of a fumigant, it does not matter if the bin is only partly filled or if filling is slow. Insecticides can also provide persistent protection, although residual insecticides can only be used where the resultant residues are permitted on the cereal grain, and recognized MRL's are not exceeded.
The condition of the grain will determine the length of time than an insecticidal treatment remains effective. Insecticide will persist much longer on cool, dry, clean grain than on warm, moist grain, that also contains excessive foreign matter.
It is important that only formulations labelled for grain protection he used. One of the following organophosphorus insecticides, (ie., pirimiphos methyl, clorpyrifos-methyl, or fenitrothion) is normally used and may he mixed with pyrethrum or a synthetic pyrethroid where control of tolerant insects, such as Rhyzopertha dominica and LGB is necessary. Organophosphorus insecticides should he applied at the rate given on the label but, as a general rule, the application rate should be not more than 10 mg/kg. Pyrethroids are applied at a rate of 1-3 mg/kg.
Dust or spray formulations labelled for grain protection are available, but sprays are easier to apply and generally preferable. Dust application is more difficult, is a greater risk to health and safety and alters the grain bulk density. Dilute dusts containing 1 percent insecticide are the least stable formulations and should not be kept long before use. A well-formulated dust from a reliable manufacturer may be fully active for two years, hut poorly formulated dusts may become inactive within a few weeks (Refer TDS # 17).
The usual application rate for organophosphorus sprays is 0.5 - 1 litre spray per tonne. The application of this volume of water does not significantly alter the moisture content of the grain.
Grain sprayers should be set up to give a continuously measured spray of insecticide to all grain passing into the bin or flat-hulk storage. A commercial grain sprayer consists of a pump, suction hose and filter to be placed in a tank or drum of dilute insecticide emulsion, by-pass hose to provide agitation in the tank, spray hose leading to a pressure regulator, pressure gauge, lance and nozzle. A reserve insecticide tank is needed to allow for continuous use. The sprayer should he fixed to the conveyor as close as possible to the point where the grain is discharged into the bin or bulk warehouse. The grain should be treated after drying and cleaning but not while it is still warm from the drier. The equipment must be placed where it can be easily inspected and serviced. Considerable quantities of water may be needed and the water source should he close to the spray tank. If there is only one sprayer for several bins, it must he portable. The nozzle should he mounted about 20 cm above the grain band. The sprayer should he connected and controlled to start spraying when the grain begins to flow and, equally important, to stop spraying when the conveyor stops. The application rate should he set according to the grain flow rate and adjusted if the grain flow is changed. It is, therefore, necessary to, know the rate of flow of the grain, and from this to calculate the required rate of spray flow. The required rate of flow for insecticide spray is obtained by choosing appropriate nozzles and spraying pressures, which should he given in the manufacturer's instructions.
Frequent checks are necessary to ensure there is sufficient dilute insecticide emulsion in the spray tank, to adjust the spraying pressure when necessary, to obtain the correct application rate, and to maintain nozzles and filters clean and undamaged. Constant attention may be needed to prevent blockage when treating dusty grain. The sprayer should be checked and filters cleaned daily.
3.4.2.2.1. Results of recent trials:
Field verification trials with a number of organophosphorus/pyrethroid mixtures of emulsifiable concentrate formulations, were undertaken in Tanzania during 1993. The combinations were applied to both hulk maize stored in metal bins and to maize subsequently bagged and kept in bagged stacks within a typical warehouse/godown in Dar es Salaam. The insecticide treatments investigated were the following combinations of emulsifiable concentrate formulations:
|
2 mg/kg permethrin |
+ |
8 mg/kg pirimiphos-methyl |
|
0.5 mg/kg deltamethrin |
+ |
8 mg/kg pirimiphos-methyl |
|
0.5 mg/kg deltamethrin |
+ |
8 mg/kg chlorphyrifos-methyl |
The results showed that the residues of all the insecticide combinations followed a declining trend with time, such that between 20 and 50% of the initial dose remained after seven months. The deltamethrin+ pirimiphos-methyl combination appeared to he the most stable and declined the least over the nine months. There appeared to he little difference in the decay observed during storage in bins and hag stacks.
The bioassay results also showed that the deltamethrin combinations produced 100% mortality of adult P. truncatus and Sitophilus spp. for a period of nine months, whilst permethrin + pirimiphos-methyl treatments in bins began declining in effectiveness after four months. In addition, the deltamethrin combinations completely prevented F1 adult production for both species, throughout the nine-month study period.
Samples treated with these chemical combinations did not exceed the recommended maximum residue limits established by the Codex Alimentarius Commission for whole grains, which are:
|
permethrin |
2 mg/kg |
|
deltamethrin |
1 mg/kg |
|
pirimiphos-methyl |
10 mg/kg |
|
chlorpyrifos-methyl |
10 mg/kg |
Maize to be stored tree of live insect pests should, after initial fumigation, he treated with any of the insecticide mixtures noted above by the application of dilute sprays. Grain to he stored in a silo should he sprayed on entry. The following rates are recommended for insecticide application to stored maize destined for transport and long-term storage in areas affected or threatened by Larger Grain Borer:
|
2.0 mg/kg permethrin |
+ |
8.0 mg/kg pirimiphos-methyl |
|
0.5 mg/kg deltamethrin |
+ |
8.0 mg/kg pirimiphos-methyl |
|
0.5 mg/kg deltamethrin |
+ |
8.0 mg/kg chlorpyrifos-methyl |
Grain properly treated with the deltamethrin mixtures should remain free of pests for at least nine months storage, whilst treatment with the permethrin + pirimiphos-methyl combination should provide effective protection for at least five months.
The estimated costings for the application of an insecticide combination of permethrin 25% EC and pirimiphos-methyl 50% EC to maize 0.4% of the market price of the commodity when sold in Dar es Salaam. (0.07 US$ per 100 kg).
The figures presented in Table 3.4.1 are estimates of the cost spraying maize with contact insecticides prior to transportation by rail The cost-estimates for the combination of permethrin and pirimiphos methyl are based on local values. The control strategy relies on the phases: initially, on the admixture of insecticide with the maize on conveyor belt during loading into the silo, and secondly, on the rail wagons being sprayed with a residual deposit of insecticide on the interior and exterior surfaces immediately before loading from the silo. The tarpaulin cover is sprayed in situ, when the wagons are full loaded. The costs illustrated are only the estimated marginal costing of the quantities of insecticide required to treat the maize:
Table 3.4.1. Estimated marginal cost of spraying hulk maize for subsequent transport by rail
|
Insecticide |
Cost per US.$ |
|
Permethrin 25% EC |
11.4 |
|
Pirimiphos-methyl 50% EC |
24 |
|
Admixture treatment to maize | |
|
Silo containing 1,200 tonnes | |
|
Admixture rate: permethrin 2 mg/kg + pirimiphos-methyl 8 mg/kg | |
|
Quantity of permethrin a.i. required to treat silo |
2,400 g |
|
Quantity of pirimiphos-methyl a. i. Required to treat silo |
9,600 g |
|
Quantity of permethrin solution required to treat silo contents |
9,600 g |
|
Quantity of pirimiphos-methyl solution required to treat silo contents |
9,203 g |
|
Marginal cost of treating 1,200 tonnes with permethrin |
109.44 $ |
|
Marginal cost of treating 1,200 tonnes with pirimiphos-methyl |
460.08 $ |
|
Marginal cost of insecticide admixture treatment |
570.00$ |
|
Cost per tonne of treatment |
0.475 $ |
|
Surface treatment of wagons | |
|
Load of each wagon |
50 tonnes |
|
Wagon surface treated + interior, exterior and tarpaulin |
170 sq m |
|
Spray rate = insecticide spray per wagon |
5 l/wagon |
|
Application rate: permethrin 0.5 g/sq m + Pirimiphos-methyl 1 g/sqm 1,200 tonnes contained within 24 wagons | |
|
Total area treated 4,080 sq m |
4,080 sq m |
|
Permethrin treatment 2,040g of a.i. |
8,160g of EC |
|
Pirimiphos-methyl treatment 4080g of a. i. |
8,160g of EC |
|
Marginal cost of spray treatment |
290.28 $ |
|
Marginal cost of combined insecticide treatment |
860.0 $ |
|
Other costs not included are staff time and equipment | |
|
Marginal cost of insecticide treatment per 100 kg of maize |
0.07$ |
|
Market price of 100 kg of maize |
19.0 $ |
|
Marginal cost of treatment as percentage of cost of 100 kg of | |
|
Market price of 100 kg of maize |
19.0 $ |
|
Marginal cost of treatment as percentage of cost of 100 kg of maize |
0.40% |
Exchange rate: 1 US$=371 TSH - 1 £=1.5 US$
3.4.3.1. All pesticides must he considered in some way potentially harmful to man and should only be used by trained personnel. In particular, concentrated insecticide must he handled with extreme caution and washing water must he available to operators.
3.4.3.2. Protective clothing should be available and rubber gauntlet gloves should be worn whenever concentrated insecticides are handled. Respirator must always he worn whenever insecticide dusts and sprays are mixed or applied. When mixing concentrated insecticides with water or other diluents, a spoon or other stirring implement should be used rather than the hand. During this operation, especially if the store room is small, the door should be left open to prevent a hazardous build-up of dust or fumes. Lids should be replaced on containers of concentrates immediately after use.
3.4.3.3. Before using any insecticide the label on the containers should be read and the instructions of the manufacturers should be followed. The correct rate of application should always be used, especially where the insecticide is being added directly to food commodities. Equipment to be used for applying insecticides should be checked before the treatment is started.
3.4.3.4. All insecticides should be stored in clearly labelled containers in a sate place under lock and key. Storage should not be in the main warehouse where food is stored, but in a separately designated room. Insecticides should not be stored in or adjacent to living quarters. Storekeepers in charge of insecticides must he properly trained. They must not eat, drink or smoke in pesticide stores. All insecticides must be checked into and out of stores and a record, with full details, kept. Large stocks of insecticides are best avoided since they can deteriorate quickly at high temperatures and humidities. Efforts should he made to ensure that sufficient insecticides for one season only are stored wherever possible.
3.4.3.5. Further information on this subject is provided in the specific technical guideline supporting the international code of conduct on the Safe Distribution and use of Pesticides or the GIFAP guidelines for the safe handling of pesticides during their formulation, packing, storage and transport. (Refer to References).
