8.5 Pesticide Selection
In the EU, fumigants, rodenticides and other pest-control products used in stores, are also legalised under Biocides regulation EU/528/2012, which entered into force on 1 September 2013 (replacing the Biocidal Product Directive: 98/8/EC). This environmental legislation [1] covers a very diverse group of products and aims “to provide a high level of protection for humans, animals and the environment”, and harmonise the European market for biocidal products and their active substances.
The following pesticides are known to have been used recently in cocoa warehouses:
| Pesticide | Info |
|---|---|
| Fumigants in IRAC MoA group 24: Mitochondrial complex IV electron transport inhibitors (i.e. insect energy metabolism) | Precursors of the fumigant gas phosphine (PH3 boiling point -87.4°C, v.p. 3465 kPa @ 20°C): aluminium phosphide and magnesium phosphide slowly release PH3 by reacting with moisture. |
| Fumigants in IRAC MoA group 8: Miscellaneous non- specific (multi-site) inhibitors including halogen-based compounds. | Methyl bromide (B.p. 3.6°C, v.p. 190 kPa): is no longer permitted in the EU and still in the process of being ‘phased out’ in N America and SE Asia. Sulfuryl fluoride (B.p. -55°C, v.p. 1700 kPa): a proposed alternative, is now permitted (Directive 2009/84/EC) |
| Surface treatments: These must be used with great care to avoid high residue levels. Note: approvals for certain products (including pirimiphos-methyl) for such treatments may soon be revoked in the EU. | Pyrethroids (IRAC group 3): natural pyrethrum, cypermethrin, deltamethrin |
Following the withdrawal of methyl bromide in the EU and concerns over residues of non-fumigant insecticides (e.g. admixtures and sack treatments described above), there were grave concerns about increased reliance on the use of phosphine with associated concerns about the onset of resistance.
An alternative fumigant currently available, also in IRAC group 8, is sulfuryl fluoride [2] which is now approved in the EU.
However, maintaining a diversity of MoA and approaches, including the use of modified atmospheres when feasible, is strongly recommended.
Pest managers also consider factors such as time to penetrate cocoa sacks - thereby the time needed for fumigation. Although phosphine has a higher v.p. than the group 8 fumigants, it is slowly released from phosphide sachets (which provide much safer delivery of toxic, flammable PH3 gas), so it is considered better for prevention than disinfestation.
The latter was reviewed by Chaudry [3], who recommended that phosphine fumigation should only be carried out by trained staff to ensure:
- Acceptable standard of gas-tightness of the area under fumigation
- Appropriately-timed application of optimal doses, and maintenance of the exposure over a minimum required length of time
- Regular monitoring of gas concentrations, to ensure maintenance of effective levels
- Post-fumigation assessment of the effectiveness of each treatment
- Integration with other methods (e.g. surface treatments with approved residual insecticides, or provision of a physical barrier) to reduce the risk of re-infestation during subsequent storage.
