FEATURE
where appearance and lack of pesticide
residues are important criteria. For growers of
major field crops, where rapid and effective
pest control and the cost of inputs are more
important, biological control just doesn’t get
a look in.
The problem with using biological control on
field crops was highlighted in a study carried
out in 2004 by two environmental scientists,
Timothy Collier and Robert Van Steenwyk,
from the University of California, Berkeley,
US. They reviewed the effectiveness of 140
biological control projects on crops such as
maize, cotton and hops. This revealed that
biological control agents failed to reduce pest
populations to target levels in 64% of cases,
only succeeding 15% of the time.
This finding led the researchers to conclude
that “biological control is not currently in a
position to replace broad-spectrum pesticides
Photo: Ward Stepman, BCP Ltd
residues that led to the recent rapid rise in the select few species, whereas a chemical
There are definitely obstacles
use of biological control in Almeria. insecticide is able to kill a much wider range
to market growth in terms of
of pest species.
Specifically, this was in response to moves
formulation and application
made by a number of German and British Biological control agents are also not as
methodology.” But these
supermarkets to stop purchasing fruit and convenient to store or apply. As living
vegetable produce from growers in Almeria, organisms, biological control agents usually
obstacles are now beginning to be
following the discovery of high levels of need to be released by a grower within
addressed, with the development
pesticide residues. “This led the association a few days of receipt. They also need to
of a range of new products and
of co-operatives in Almeria to instruct their be distributed by hand, either by actually
growers – and I think I can put it that strongly sprinkling the biological agents around the
technologies
– that they will be using integrated crop crop or depositing containers at suitable
management [including biological control] this locations. Finally, biological control agents
season,” explains GreatRex. tend to be more expensive than standard in agricultural food production”. However,
chemical pesticides, simply because they there were a number of important caveats to
But despite this growth, biological control
are more costly to manufacture and aren’t this conclusion. These included that further
still tends to be restricted to a few niche
produced at such large scales. research into new biological control agents,
crops, especially salad and vegetables crops
production technologies and distribution
such as tomatoes, cucumbers, peppers and This explains why biological control has only
systems could well increase the effectiveness
aubergines. It is hardly used at all to control really been taken up by growers of crops
of biological control, as should combining it
pests on the main field crops, such as maize
and wheat, and this is because chemical
pesticides tend to be far more effective at
controlling crop pests than biological control
agents.
For a start, biological control agents are much
slower acting: insecticides start killing insect
pests immediately, whereas biological control
agents can take days to weeks. Chemical
insecticides will also reduce pest levels
down to practically zero, while biological
control agents can only reduce them to a
certain threshold, beyond which there will
not be enough pest organisms to sustain
the population of biological control agents.
Biological control agents are also usually quite
Photo: Ward Stepman, BCP Ltd
pest specific, only eating or parasitising a
 November 2007  •  www.agrow.com
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