Some cocoa pests
and diseases respond to a classical approach, while others call for an inundative/biopesticide
solution. The interactions between biological and chemical control agents may
also have to be investigated, as part of an ICM strategy. The term "biopesticide"
is most useful when applied strictly to living organisms which are (a) specific
as individual products and thus confer some environmental advantage (unlike
many but not all chemicals), and (b) have a limited ability to persist in the
environment, and are therefore usually released using pesticide application
techniques (although, more persistent, classical agents may be utilised as biopesticides).
In practice, biopesticides often are most acceptable to policy makers and the
public when indigenous isolates of control agents are used.
Trichoderma spp. are present in substantial numbers in most soils and in environments
such as decaying wood. They are being increasingly exploited
as disease control agents against plant diseases in a wide range of field and
tree crops, and promising candidates for tackling cocoa diseases include: T.
asperellum, T. koningiopsis, T. ovalisporum and T. stromaticum.
The USDA provides a very helpful key
to these species. Mechanisms of action may include direct anti-fungal activity
through mycoparasitism of hyphae and antibiotic production, and indirect effects
such as inducing host plant resistance and competing for nutrients and space.
as a strain of Trichoderma viride on cocoa witches' broom, in Brazil's
Amazon basin, T. stromaticum (Samuels et al., 2000) has proved to be
an effective mycoparasite of witches'
broom disease: Moniliophthora perniciosa. Initial small-scale field
and lab trials conducted at CEPLAC showed that it could reduce formation of
basidiocarps (fruiting bodies) by 99% when brooms were in contact with the soil,
and by 56% in brooms remaining on trees. It also reduced pod infection by 31%.
A commercial formulation 'Tricovab' was developed by CEPLAC in Brazil and is
now available for control of witches' broom, with improved formulations under
unimpaired sporulation of Trichoderma stromaticum on a witches' broom
in a plot that has clearly been treated with a copper fungicide
a cocoa weevil Pantorhytes plutus infected with Beauveria bassiana
Over recent years
there has been the development of biologically based methods against insect
pests including the development of mycoinsecticides, use of botanicals, natural
enemies and pheromones (sometimes called "biorational" agents). The potential
of using oil-based formulations to enhance the infectivity of potential mycoinsecticidal
agents such as Beauveria bassiana was first identified with the cocoa
weevil in Papua New Guinea by Dr. Chris Prior. Based on this work, a technology
was subsequently developed for control of locusts and grasshoppers, with the
development of the Metarhizium-based 'Green Muscle' mycoinsecticide. Unfortunately,
this remains a "latent technology" for a number of potential insect pests, including
cocoa insect targets, partly because of development costs. For example, in order
to turn 'Green Muscle' from an idea into a commercial product, approximately
€15 million were spent by the international LUBILOSA
Programme. Although much of this technology could be adapted for other pests,
a considerable investment would still be required for efficacy trials, optimising
production, adapting formulations, safety testing, registration etc.
Nevertheless, there are examples where biopesticide approaches might be effective
against major cocoa pests such as cocoa capsids
(various species of Miridae) and cocoa pod borer: Conopomorpha cramerella. These show promise in the laboratory, but
require further verification in the field.
Research & Development Activities
of delivery systems for Trichoderma stromaticum. A 'MycoHarvester' Mk 3 has been installed and is operational at the biological
control unit in CEPLAC.
It has completely replaced previous 'Tricovab' product handling equipment and
can therefore be considered a considerable success (having also been subject
to attention in the local media), but optimisation can be considered a continuing
Reducing the 'Tricovab' product to a pure single-spore powder creates
a number of opportunities:
dosage control is now possible: 'Tricovab'
is a reliable product, akin to its chemical rivals, which will not block filters
- Packaging and
formulation are considerably easier: with a sachet system for mixing individual
sprayer tank loads under development;
- Shelf-life of
the product should be enhanced by improved control of product moisture content
(by reducing the bulk of the product, control of ambient temperature is easier).
to achieve optimise delivery systems for biological agents:
production issues, including:
* selection of suitable isolates
* spore separation from substrate
(e.g. using the MycoHarvester)
* optimisation of storage and packaging
options under investigation/development:
* water miscible suspension
* spores in adjuvant oil
* oil based formulation for ULV application
Application (special issues with particulate suspensions)
activity of 'Tricovab' has been assessed, but more work is needed on its persistence in the
environment. It may be compatible with chemicals such as copper fungicides;
improved formulation will aid tank mixing with chemical fungicides (e.g.
for pod protection).
Medeirosa FHV, Pomella AWV, de Souza JT, Niella GR, Valle R, Bateman RP, Fravel D, Vinyard B, Hebbar PK (2010) A novel, integrated method for management of witches' broom disease in Cacao in Bahia, Brazil. Crop Protection, 29(7): 704–711.
key to Trichoderma spp. (Dr. Gary Samuels et al.)