The choice of insecticide concentration, type, and frequency of application depends on various factors, such as the pest species present, storage facility type, storage duration, and local insecticide regulations.
Therefore, only generalized recommendations can be made. Pest control strategies must combine techniques that are effective, economical, and prioritize preventing food product contamination.
These strategies must address immediate pest issues, prevent future infestationsthe judicious use of pesticides.
Unsatisfactory pest control results in contaminated products, causing health, financial, legal, and aesthetic issues. Financial losses may arise from
- live or dead insects in products and containers
- odors, webbing, and frass in products and containers
- loss of consumer confidence in the company due to these conditions; and
- direct weight loss from insect feeding.
Control of stored-product pests is essential to prevent contamination/adulteration of human foods. Individuals involved in commodity/food storage, handling, or processing are responsible for preventing food adulteration. Failure to do so may result in human illness or death, legal violations, loss of goodwill, and revenue decline.
Read Also: Pests of Stored Products and Damages Caused
Methods of Pesticide Application for Stored-Product Pest Control
1. Residual (Structural) Treatments for Storage Facilities
Residual sprays are typically applied to the inside surfaces of warehouses, storage bins, transport vehicles, or other structural surfaces. An effective residual spray kills insects on contact and deposits on treated surfaces to eliminate crawling insects.
Applications may occur during storage facility cleaning before new stock intake or in coordination with fumigation or stock spraying.
Corners, ledges, cracks, and hard-to-reach areas must be treated. The residual deposit’s effectiveness diminishes over time, depending on the insecticide, climatic conditions, and surface type.
Examples include fenitrothion, malathion, synthetic pyrethroids, and chlorpyrifos-methyl. Wettable Powders (WP) are more persistent than Emulsifiable Concentrates (EC) but harder to apply.
WP formulations are preferable for absorbent surfaces like cement, brick, stone, or whitewashed surfaces, while EC suits non-absorbent surfaces like metal or painted wood.
Insecticides persist longer on wood. Malathion is less effective on alkaline surfaces (e.g., whitewash, bare concrete, or cement) but remains active for over 20 weeks on plywood and fiberboard, and 16 to 52 weeks on other surfaces.
Treatment frequency depends on the insecticide and infestation type. For instance, lindane and malathion treatments require reapplication every three weeks in tropical climates.
Pyrethroids and carbaryl outperform organophosphates (OP) against Rhyzopertha dominica, while OP are more effective against Sitophilus spp.
2. Space Treatments for Flying Insect Control
Space spraying or fogging in warehouses targets flying insects uncontrolled by residual treatments or those migrating from outside. It requires frequent application, typically at dusk when pests are most active.
Insecticides with knockdown action, such as pyrethrin sprays, aerosols (with or without synergists), synthetic pyrethroids, lindane smoke, fog, or dichlorvos aerosols and strips, are used.
Aerosols are dispensed from canisters containing liquefied gas and insecticide, which “blasts” the mixture into aerosol-sized droplets via nozzles. Slow-release dichlorvos plastic strips, hung at one strip per 30 cubic meters, effectively kill flying moths.
3. Grain Protectants for Direct Grain Treatment
Grain protectants are pesticides incorporated directly into grain to protect against insect and mite attacks, also known as admixture treatment. These insecticides, of low mammalian toxicity, are safe and require simple application equipment.
They are applied as sprays into the grain stream during movement or at the start of long-term storage. Suitable equipment includes electrically operated pumps with precision nozzles or pressure-retaining knapsack sprayers for areas without power.
EC are typically used, with volumes not exceeding 2.5 liters per 1000 kilos of grain to avoid moisture increase. Precision apparatus is most efficient for bulk handling but viable for bag systems.
Small pumps with coarse nozzles and low pressure produce large droplets, minimizing drift. In drip-feed systems, tiny quantities of concentrate are dripped into the grain stream via micro-capillary tubes.
For small-scale bulk or bagged grain, dusts are mixed using mechanical aids (e.g., rotating drums, shoveling), though adequate mixing is challenging.
Read Also: Collection, Handling, Storage and Pre-Treatment of Seeds
4. Fumigation for Comprehensive Pest Control
Fumigation is widely used for stored-product insects, as fumigants penetrate areas inaccessible to other methods. A fumigant is a chemical existing as a gas at specific temperatures and pressures for a prescribed period.
Fumigation involves applying gas under conditions to control target organisms. Fumigants vary in composition, formulations, handling, analysis, and use. Selection depends on effective, economical control without harming the commodity.
All fumigants are toxic to humans, potentially flammable, corrosive, odorous, phytotoxic, or residue-leaving. Some are suspected carcinogens, requiring precautions to avoid exposure.
Fumigation must control insects without damaging commodities or endangering personnel. Effective detection and analysis methods are critical to prevent accidents.
Common fumigants include pirimiphos-methyl (Actellic EC), aluminum phosphide (Phostoxin), and dichlorvos, used for bag stacks under gas-proof sheets or bulk with air recirculation.
Phosphine is efficient for horizontal grain bulks and vertical storage where methyl bromide is unsuitable. Exposure must ensure adequate duration and gas concentration.
For cereals in international trade, a tolerance of 0.1 ppm (expressed as PH3) is recommended.
5. Surface Sprays for Grain and Bag Protection
Surface sprays treat bulk grain surfaces or outer bag surfaces, using insecticides like pyrethrum with piperonyl butoxide, dichlorvos, malathion, pirimiphos-methyl, chlorpyrifos-methyl, and tetrachlorvinphos.
Bag stack treatments include the “sandwich” method (layer-by-layer spraying during stack construction) or external stack spraying to prevent reinfestation, typically post-fumigation or pre-sheeting.
Common insecticides include malathion, pirimiphos-methyl, and fenitrothion at 1–2%.
6. Sack Treatments for Long-Term Protection
Sacks are sprayed (50 ml/m²) or dipped in insecticide solution before filling with grain and air-dried post-treatment. Malathion, pirimiphos-methyl, and chlorpyrifos-methyl at 2–4% are effective.
At 2%, malathion lasts 2–4 months, while pirimiphos-methyl and chlorpyrifos-methyl last 4–6 months. At 4%, these compounds control infestations for 9–12 months.
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Frequently Asked Questions
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