4.7 Efficacy (including AI mixtures)
There are two approaches to the regulation of efficacy of plant protection products:
- A view that ‘the market will decide’ about efficacy and that the primary role of regulation is to ensure safety. This is considered appropriate in the USA and elsewhere, with farmers often benefiting from sophisticated agricultural extension support networks.
- More ‘interventionist’ policies (as in Europe): where toxicology studies are likewise emphasised, but companies must also demonstrate efficacy against key target pests in order to obtain registration.
A view taken in many cocoa growing countries is that farmers should be supported with advice on effective products, often via Government research and extension agencies. As described above, the list of pesticides that are suitable for use with cocoa has changed dramatically over the past decade, in light of changes to the regulatory environment in the EU, Japan and other importing countries.
With the recent controversy surrounding the neonicotinoids, currently a ‘strategic’ MoA for the crop, research and Registration Authorities must maintain an ongoing review of registered pesticide products appropriate to 21st century needs.
However, as with other crops, policymakers must also foster a strategy for ‘sustainable intensification’: in this case maintaining a diversity of appropriate and efficacious range of active substances, preferably belonging to 3 or more MoA, for control of key cocoa pests.
This objective has been a factor when compiling the list in Appendix 3A.
In many cocoa growing countries, the withdrawal of older (and sometimes not so old), neurotoxic compounds has not been accompanied with commensurate adoption of newer products: so insecticides currently available in cocoa growing areas belong to only 2-3 MoA, often dominated by pyrethroids. This has potentially deleterious consequences for both integrated pest and resistance management strategies, besides perpetuating outdated pest control perceptions amongst farmers.
In addition, chemical control against key insect pests was often established using compounds with fumigant action (e.g. HCH, endosulfan) that helped to compensate for poor application; this property is no longer acceptable to Regulatory Authorities.
Researchers must therefore adapt mid-20th century protocols for pesticide screening where the end-points of assays rarely exceeded 48 hours, thus excluding many IPM-compatible non-neurotoxic substances (and possibly biological agents) that constitute a majority of the known insecticidal MoA.
A further difficulty, illustrated below and a notorious problem with cocoa mirid experiments, is that control mortality increases over time to levels that exceed standard analytical assumptions.
Over recent years, the number of products (including those of research-based companies) that contain mixtures of insecticide AI has risen substantially.
Whereas there has long been a resistance management narrative for AI mixtures of fungicides with very specific target biochemistry, entomologists have generally discouraged insecticide mixtures because of the likely impact of insecticide mixtures on non-target organisms.
IRAC has now brought out a document on this issue [1] which includes the following statements:
- In the majority of settings, the rotation of insecticide modes of action is considered the most effective IRM approach.
- Most mixtures are not primarily used for purposes of IRM.
Mixtures of insecticides may provide commercial advantages for controlling pests in a broad range of settings, typically by increasing the level of target pest control and/or broadening the range of pests controlled.
There are cases when they help with combating a pest complex using a single spray (such as in cotton pest management) but broadening the spectrum of activity can quickly compromise IPM.
There is a risk that mixtures use more chemicals than are genuinely required and a number of regulatory agencies are essentially opposed to their use.
