Fungicide delivery systems for cacao
Centro Agronómico Tropical de Investigación y Enseñanza (CATIE) (Costa Rica), Mars Plc.
Problem/Issue. Fungal diseases are a principal constraint to world cocoa production and two of these - witches' broom and frosty pod rot - pose a special threat to livelihoods in Latin America. Chemical controls have been expensive and of limited efficacy in this complex ecosystem, so biological control agents, together with varietal improvement, probably offer the most sustainable long-term solution. Although widely liked by IPM protagonists, many microbial agents will remain scientific curiosities unless technical, commercial and conceptual issues of biopesticide development can be resolved. More biopesticide products must appear on shelves and farmers must want to use them. Amongst their perceived constraints are narrow target spectra, poor performance relative to cost, and inconsistent product quality. However a major problem with current use is the poor standard of application to crops, allied with a belief that horizontal transmission mitigates the need for good delivery systems. Various studies have shown that, as with chemical pesticides, formulation, spray droplet size and coverage can substantially affect the efficacy of biological agents. 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 cocoa, are often especially poor. In practice 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.
Project Activities. The primary aim of this project is to improve delivery systems (especially formulation and application techniques) for promising microbial agents such as hyperparasitic fungi in the genera Gliocladium and Trichoderma. The techniques developed may also be used in the application of conventional chemical fungicides, which will continue to be used as standards in the field-testing programme. The project is closely linked with the CABI Bioscience strategy for management of cocoa disease in Latin America using microbial biological control agents.
Achievements So Far
The project started with the preparation of a guide to biopesticide application given in a workshop manual (Eds. U. Krauss & P. Hebbar, 1999) (Download Workshop Manual PDF). This was followed by spray droplet size studies on potentially important nozzles for cacao disease control. Techniques are now being studied in a large factorial trial in La Lola, Costa Rica. The objective is to investigate delivery systems (application techniques and presence of an emulsified oil adjuvant) that may influence the effectiveness of agents to control Moniliophthora roreri and associated cacao pathogens.
The project will continue to carry out field testing options for delivery of biological and chemical agents in factorial field tests. These trials have triggered associated work that must be carried out on spore separation and biopesticide quality control.
The choice of control agents is also crucial, and the use of biopesticides appropriate for cocoa may provide ideal technical solutions, when efficacious products become available.
In the short term however, answers are needed to the question: 'What would we recommend if cocoa prices were to rise dramatically enough for farmers to want to use fungicides again?"
Unfortunately there is very little literature on impartial research into pesticidal control carried out in the past decade. It is probable that most farmers would resort to copper fungicides that are neither particularly efficacious nor environmentally sound. Since the days of high cocoa prices, much has happened to the pesticide market, including the introduction of whole new chemical classes of compounds. Perhaps of equal significance, the patents on useful molecules (such as triazole fungicides) have expired, raising the prospect of using products that were previously considered too expensive.
The short- to medium-term rational pesticide use (RPU) goal is therefore to assemble a 'tool kit' of practical, efficient and safe solutions to key problems, and encourage farmers to adopt them. This may include the preparation of resource materials (extension manuals, etc.) and training.
Roy Bateman (Co-ordinator) firstname.lastname@example.org
Start date: 1999
End date: 2001