4.5.3 Herbicides and sprouting inhibitors

Herbicides, or weed killers, occupy the largest global share of the pesticide market, although their use by smallholders is limited in comparison with intensive farming, amenity weed control, etc. Perhaps their greatest use in cocoa is in larger-scale, commercial plantings. 

They are most typically applied at an early stage to prevent young plants from being choked by weeds. Control is rarely required once the canopy closes (although mistletoes may become a problem in poorly managed cocoa).

Herbicides have been classified in several ways and, as with other pesticides, a number of chemical families can be grouped by their modes of action (using letters in the HRAC nomenclature). 

In practice, herbicides are often grouped according to their mode of use:

• Contact herbicides, where only the part of the plant sprayed is killed, such as the photosynthesis inhibitors paraquat and diquat (MoA group D);
• Systemic - pre-emergent and post-emergent herbicides include compounds that:
  • disrupt amino acid synthesis in chloroplasts, e.g. various salts of glyphosate (group G);
  • disrupt cell division in broad-leaved weeds: including synthetic auxins such as 2,4-D, triclopyr and picloram (group O).

Triclopyr is used as stump arboricide which has a specialised use in cocoa swollen shoot virus disease (CSSVD) control campaigns: to prevent re-growth of old trees, before re-planting with improved cocoa varieties.

In registration lists and surveys, glyphosate and paraquat have been recorded as widely used on cocoa (sometimes under “plantation crops”). 

After its patents expired, glyphosate became the world’s top-ranking pesticide by sales, usually available as two salts (isopropylamine and trimesium), from a wide range of companies. 

Perhaps for this reason, it has received considerable criticism over the past decade, with claims about health risks (such a non- Hodgkin’s lymphoma) and, perhaps more convincingly, its impact on soils and the environment with continuous use. [1] 

For these reasons, Registration Authorities appear to be withdrawing glyphosate in favour of glufosinate- ammonium, which has a slightly different mode of action (see Appendix 3).

It is important to appreciate that herbicides such as these are:

• treated as pesticides - certainly for scientific and regulatory purposes - even though many commercial operations consider weed control functionally as part of agronomic practices (as opposed to “poisons” used for other pest control);
• permanent crops such a cocoa constitute only a tiny part of the world pesticide market and even there principally used for land clearance, rather than regular applications to established cocoa crops. In this respect, agrochemical companies are interested principally in their use in conjunction with (often genetically modified, e.g. “Roundup ready”) annual crops. The synthetic auxin herbicide
• The synthetic auxin herbicide, 2,4-D has caused considerable concern, appearing as residues in cocoa beans from more than one country. The active substances include a number of salts [2], acids and esters, some of which are moderately volatile (vp of acid = 1.9 x 10-2 mPa) and have a characteristic odour. In some cases, it transpired the residues originated from the ground on which the cocoa beans had been dried (roadsides, courtyards, etc.) had been previously treated with herbicides, or exposed to run-off after rain. The use of drying mats for cocoa beans, elevated off the ground, is therefore an important SPS recommendation and it is vital that exposure (including vapours) to cocoa beans is avoided at all stages in the supply chain, including storage and transportation.

In principle: 

• Approved herbicides present a low risk when used judiciously for weed management in establishing trees
• …which especially means care in application: avoiding the production and drift of small droplets onto non-target areas.
• Care and oversight is needed along the whole cocoa bean production and supply chain
• …herbicide residues may originate from outside the cocoa garden.

In African and Asian cocoa-growing countries, glyphosate-based registered herbicide products dominate, with the more acutely toxic group 22 compounds such as paraquat still available in South America (see Appendix 3). 

They may not be specifically registered for cocoa, but there is a general usage especially in "Plantations" for land clearance.