6.2 Spraying equipment for field pests
The method of pesticide application is crucial, but it is often a more neglected aspect of pesticide use.
Applying less, by applying more efficiently, should be a fundamental maxim in IPM, yet practices have not improved over recent decades in many countries: in some, standards have actually gone down.
Together with attention to pre-harvest intervals (PHI) and number of sprays, careful application is one of the ways in which pesticide residues can be controlled, since it determines the dosage delivered to the crop.
Whether a chemical, biological or ‘biorational’ pesticide is to be applied, the performance of a good control agent will be severely reduced by poor delivery systems [1], so application is also a key factor to achieve efficacy.
In practice, there are a number of important considerations in pesticide application:
- Assessing the target and equipment selection
- Health & safety
- Nozzle selection and setting
- Calibration
- Application technique
- Maintenance and repair of equipment
Further detailed information is available in Pesticide Application Methods [2], with notes also available online at https://www.dropdata.net/
There are essentially two types of equipment commonly used for spraying cocoa trees: motorised knapsack mistblowers (or air-blast sprayers) and manual (hydraulic) sprayers.
- Almost all smallholder farmers use manual (hydraulic) sprayers, which are globally the main method of pesticide (especially fungicide) application to cocoa.
- Motorised mistblowers now have many uses, but they were originally developed for obtaining good droplet coverage in the tall cocoa trees of West Africa.
Chemical control of both mirids in Africa and cocoa pod borers in South-East Asia was initially validated using insecticides such as lindane and endosulfan, whose volatility helped overcome deficiencies in application.
Nevertheless, it was estimated that less than 0.02% of active ingredient reaches the biological target when applying control measures to cocoa using motorised mistblowers [3].
Newer chemical products may be substantially more expensive than the more familiar generic compounds used hitherto, and volatility is no longer an acceptable property for insecticides, so improving the quality of application has become most important.
FAO provides guidelines on the minimum requirements for agricultural pesticide application equipment [4], but unfortunately in any visit to sprayer stores or farmers in the many cocoa growing areas, it can be difficult to find equipment that complies with these requirements.
For portable equipment (as used by most farmers and especially smallholders), specifications are given for sprayer tanks, pumps, etc., with specific requirements on nozzles (see below).
FAO envisaged that member countries should put sprayer quality standards into law as with pesticides, but sadly, few countries have implemented this; however in 2008, Cameroon changed a statute to include the prohibition of import of sprayers that do not comply with FAO Minimum Requirements.
