Pests are a contentious issue. Their fright and scare
are biblical, no doubt. Yet the emotions their very appearance stirs have
allowed the agro-chemical complex to introduce final solutions, whose impact on human health is ambiguous while
their economic benefits for the farmers have proved elusive.
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| A stem borer |
A common stance on pests situates them in a linear
relationship between a cause – the pest -, and an effect, - the plant disease -.
Pests cause diseases among trees, such as those in Luntian Farm, as well as
annual crops, such as the rice we grew in the past and we intend to grow again.
In the linear presentation of the problem, pests cause death of plants and loss
of crops. Hence, the solution is just to remove the cause: kill the pest, the
plant will thrive.
If we look at the stem borers burrowing through our
cacao trees or digging into our marang
(Artocarpus odoratissimus) saplings, we cannot but agree that here we have the agent
behind a plant disease. Indeed we do
So why we didn’t cure it with powerful biocides? Is a
green ideology blinding us to the harm inflicted by this “monster”?
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| Eulophonotus myrmeleon (cocoa stem borer) |
Hard to say:
ideologies and faiths play a role we cannot discount. Even in our own work in
the farm. And, for sure, those stem borers have harmed the cacao.
But the cacao tree, even if heavily infested, did not die.
So far it has resisted the invasion.
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| Cacao tree (Theobroma cacao) resisting a stem
borers' assault |
Borers have exacted their toll from marang saplings,
as well. They hollowed out completely the upper stems of a few marang’s – known
sometimes as Johey Oak -, leaving just the lower trunks and their roots.
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| This marang lost the whole
upper stem to the borers |
A few died. But several survived developing lateral
stems.
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| A lateral stem has grown to replace the portion
lost to the borers |
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| Recovering marang tree |
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| New shoots on a cashew |
The causal relationship between pest and plant disease
at least implicitly assumes a permanent and severe damage to the tree and its
functions: generally its death. But this assumptions is hardly evident walking
across the fields and working with trees and plants. On the contrary: trees have
a large arrays of strategies to fend off malicious pests.
And, even under the fiercest attack, we should not
take for granted the death of the plant.
The cashew in the pictures beside and below underwent a severe
aggression by a major pathogen, a fungus (Lasiodiplodia
theobromae) that generally leads to gummosis, a serious fruit tree disease.
We thought the tree was bound to die, as the gummy patches had spread and the
plant profusely discharged exudates from its wounds. It did not die, as these
pictures show
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| Recovering from gummosis |
So what? Are we here proposing an acquittal from
murder for lack of consistent evidence?
Not really. The idea instead is to question the linear
sequence pest-plant disease-death, and replace it with a model where pests
interplay with many other factors in determining the health of a tree. The
interplay among those factors explains why a marang might be killed by the borers
and another not, why a cashew may succumb to gummosis while another survives. Soil,
water, weather, tillage, harvesting practices and the tree’s own adjustment to
its surroundings are all contributing factors, in the interplay that causes
health and disease. Other living organisms, animals and plants that share the
same space, are factors too.
Thus, there is no final solution: a biocide to kill
off the individual, malevolent pest. Only strengthening the positive interplay
among multiple agents, some obvious others not, we can treat the tree. This
positive and complex synergy is probably a good way to present organic
agriculture.
