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© ver. 9/4/2012

A Guide to Safe and Efficient Application for Chemical and Biological Pest Management in Commodity Crops

Commodity crops such as cocoa and coffee are attacked by a number of pest species including fungal diseases, insects and rodents - some of which (e.g. coffee rust, frosty pod rot and cocoa pod borer) have increased their geographical range dramatically, and are sometimes described as "invasive species".

 

Farmers - most of whom are smallholders - when faced with these problems seek effective solutions, and many (but not all) turn to the use of pesticides to provide remedies. Such practices often do not sit comfortably with the concepts such as sustainabililty and environmental well-being.

Most scientists now agree that pest control is best achieved within a framework of "Integrated Pest Management" (IPM) - or more generally "Integrated Crop Management" (ICM). These are terms used to describe the best mix of pest management techniques including:

  • Cultural methods, such as removal and burning of diseased plant parts, pruning, removal of infected/infested pods/berries and regular complete harvesting.
  • Clonal selection and other genetic methods as long-term measures (much of the research currently taking place is unlikely to be implemented until well after 2010).
  • The preservation and/or manipulation of biological agents (e.g. biopesticides and insect predators such ants).
  • The use of chemical pesticides.

Cocoa: the background to these issues and our current activities with this crop, including:

Photo (right):
honey and cocoa production in Ghana
(in a farm where pesticides are used).


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Issues with chemical control:

Chemical controls have been expensive and of limited efficacy in such this complex ecosystem, so biological control techniques, together with varietal improvement, may offer sustainable long-term solutions. Nevertheless, pesticide spraying is a commonly practised by cocoa farmers in various parts of the world, and we explore ways in which safety and efficiency can be maximised. Rational Pesticide Use (RPU) is about identifying and mitigating the real problems (as opposed to popular fears) in pest management. These include cost effectiveness, safety and "sustainability" issues including:

  • Efficacy: especially identifying agents for the control of invasive insects and diseases.
  • Cost of pesticides: perhaps of greatest interest to many farmers.
  • Safety: especially with certain neuro-toxic insecticides.
  • Residues: this problem especially brought to public attention with former gamma HCH (lindane, gammalin) sprays against insects. More recently, the European Union has decided to extend regulations on pesticide residues to imported commodity crops.
  • Resistance: especially with fungicides for control of Phytophthora spp. and insecticides used against cocoa mirids and CPB.
  • Concerns about the long-term use of copper for disease control (although not yet from regulatory authorities).

 

Pesticide Selection

Insect pest and disease control strategies that rely on the application of a limited number of pesticides are almost certainly not sustainable. A research and extension "vacuum" in appropriate pesticide research since the late 1980s, combined with years of poor returns for cocoa crops, means that most smallholder farmers often apply older, often more hazardous, products and are unaware of recent control agents and techniques for pest management. There is now an urgent need for programmes that transfer RPU techniques from laboratory to field to marketplace, and in each of the major cocoa growing regions, address questions such as:

  • What are the true levels of control and operational costs (over large areas)?
  • Can we replace all the hazardous (WHO/EPA class I and II) currently-used products in the near future?
  • Are there effective control agents that also have a minimal environmental impact?

High pest pressure, infrastructure, even crop, and most of all: organisation and enthusiasm: the elements for performing successful field trials.

Technical issues include:

  • What are the most appropriate ways of screening control agents, before going to the expense of carrying out field trials?
  • How best to design trials on a variable crop such as cocoa?
  • Most cocoa farmers are smallholders, but will trials on their farms produce answers quickly enough?


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Application

We believe that some of these problems, and therefore possible solutions, start at the point of pesticide application. Spray application of pesticides (be they biological or chemical) is usually highly inefficient, and the techniques used by smallholder farmers for tree crops, such as cacao, are often especially poor. It is common to encounter knapsack sprayers, fitted with cone nozzles, being used to "squirt" the tank mixture onto higher branches; most of the liquid then falls back onto the ground and is wasted. We provide a simple 10-panel guide giving, what we think are, the most important points smallholder farmers should consider when applying pesticides to cocoa. The benefit/cost of applying pesticides may be further increased by improved timing of application: but these studies are still at an early stage with cocoa.

After application, how much pesticide in a sprayer tank (be it chemical or biological) ends up on the ground?

"Spray to run-off" may mean "spray and pray"...

  • What is the best nozzle setting for maximising treatment of pods?
  • Scientific supporting data (droplet size spectra)
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