6.1 Application rate (the theory and the label)
Improving the efficiency of application has the potential to improve pest control, reducing both pesticide costs to the farmer and loading on the environment; spraying less to achieve at least equivalent efficacy may even reduce residues.
However, only in the most sophisticated spray operations is any attempt made to control the various factors that affect spray deposition on crops.
In practice, the smallholder cocoa farmer can best assess the number of trees per tank-full (see calibration sections below). It is rarely appreciated just how inefficient normal existing application practices are in crops.
Winteringham’s work [1] highlighted the inefficiency of dose transfer to the biological target; when lindane sprays were applied to cocoa mirids, only 0.02% of the total leaving the tank reached the biological target.
Exceptionally, efficiency may reach 30% for herbicide sprays on grass weeds; thus at best, perhaps only 70% of the pesticide mixture in the tank is wasted!
In general, experience has shown that for most spray operations, calibration is most effective when it focuses on the volume application rate (VAR). By mixing in a known quantity of pesticide formulation, an accurate dosage is applied to the target area (a group of trees, a field, etc.).
It is important to distinguish dosage from dose: which is an exact quantity of substance delivered to an individual organism (e.g. in a bioassay). VAR in itself makes little difference to the quality of deposit, which is dependent on the various interacting factors shown below.
From this, an appropriate formulation dilution rate is calculated to accurately achieve a certain dosage per tree or per hectare.
In practice, such calculations are only rarely made by operators. Attention to product labels is far from general practice, but labels remain the most available source of information to farmers and spray operators.
However, even label application rates can be flawed if more than one type of sprayer is used in an area, since typically they assume a given (often very high) VAR will be used.
For tree crops such as cocoa, the pesticide label will give application rate in the form of a recommended tank mix concentration; good labels may also give useful advice on application.
Unfortunately, this is displayed on a bottle containing a hazardous (Class I) insecticide that has now been superseded. Although the pictograms (at the bottom of the label) indicate the need for protective equipment, the operator illustrated just above is using a motorised mistblower, but wearing neither a face-visor nor ear defenders (see section 6.5).
The product label provides the means of communication between the producer, the regulator and the farmer (or his/her advisor). As such, labels are crucially important and therefore must be a key part of regulatory scrutiny.
National regulators have labelling policies and labels must always be written in the appropriate local language(s), but international advice is available on harmonising label formats, which will have similarities to those of standard pesticides.
An example is shown below. It is incumbent on regulators to establish whether the information on the label is compatible with GAP and that a mechanism is in place for checking the quality of the contents.
6.1.1 Consumer protection, operator safety and GAP
Before finishing this description on pesticide labels, it is important to stress the need for rigorous registration and label approval processes for permitted products.
National pesticide guides that focus on locally recommended plant protection products are increasingly being published and are an important source of information on trade names, recommended application rates for different crop uses, etc.
Where they are not available (or difficult for farmers to obtain), provision of such guidance, in a user-friendly form, is an important role for Government and NGO extension agencies.
