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Cultural Management of Corn Borer
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Masipag News & Views
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Dec 08, 2001 04:13 PST
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CULTURAL MANAGEMENT OF CORN BORER
(Why Farmers Don't Need Bt-Corn)
Giant agrochemical firms Monsanto and Pioneer always say in their
propaganda blitz that corn borer infestation is the very reason why they
want Bt-corn tested and eventually commercialized in the Philippines.
A high 20% to 80% losses in corn are attributed by these firms to corn
borer attacks in the country. However, little is known that these
figures were not based on actual field studies, but rather on mere
extrapolation of a 1971 research results.
Based on recent field studies, Masipag scientists say infestation of
corn borer is at a low 13% during the main cropping season and only 6.5%
during secondary cropping period.
This decreasing trend alone makes the gene-altered corn plants
irrelevant in the Philippines. But of course Monsanto and Pioneer will
not admit publicly they simply want to recoup their huge investment
losses with today's growing rejection of genetically engineered products
in the North.
For generations, small farmers have been practicing a more effective,
safe and ecologically sound methods of pest management in corn.
Below is a listing and brief explanation of the principles behind the
farmers’ practices in the cultural management of corn borer:
DETASSELING
How it’s done: Detasseling of 75% of the corn planted in the area. One
row of corn is to remain intact for every three rows detasseled.
The Principle: A Corn borer lays eggs on the underside of the corn
leaves. Once hatched, the 1st and 2nd instar larvae go up to the tassel
to feed on the pollen – which is a rich nutrient source for them. At
this stage, the larvae can also feed of the leaves and these are
manifested only as pin hole pricks but the tassel is primarily their
food source. Thus detasseling will reduce the mass of larvae even before
they reach the 3rd –5th instar, when they start boring holes into the
corn stem, which is considered most destructive to the corn.
FALLOW CROPPING OR CROP ROTATION
How it’s done: Leaving the land unplanted or planting a crop aside from
corn following a season (of corn).
The Principle: The practice will considerably reduce any pest population
as every crop provides a different food to which not all pests can eat.
The absence of plant host will also prevent the continuance of a pest’s
life cycle and thus its proliferation.
INTERCROPPING
How it’s done: Planting peanut in between rows of corn. The practice was
found to not only reduce infestation but also replenishes the soil
nutrients used up by the corn plant.
The Principle: Researches have found that planting peanut along with
corn can reduce the corn borer population due to the following reasons:
**It is believed that from the air, some colonizing insects like the
borer adults prefer landing on areas that are of a brownish hue, such as
that usually found in a cornfield. Areas inter-cropping peanut and corn
reduce the brownish view - because of the green foliage of the peanut
crop and consequently, discouraging potential egg layers to settle
**The peanut crop serves as a host to beneficial insects that feed on
borer eggs and larvae.
RESISTANT VARIETY
So far there are no varieties known which are widely resistant to corn
borer, however, the native “Tiniguib” has shown a low infestation rate
compared to hybrid varieties.
TIMELY PLANTING
How it’s done: Synchronized planting of adjacent fields or planting
corn as a dry season crop to avoid the “peak season” of corn borers
(seasonal corn planting).
The Principle: When planting is synchronized with the rest of the
adjacent fields, severe losses in a single field are avoided since the
damages are distributed among other corn farms. Seasonal corn planting
can significantly reduce corn borer damage since high infestation rate
occurs only during the rainy season. These differences were attributed
to the occurrence of intermittent heavy rainfall and strong hard winds,
which in many ways affected insect flight and migration. Therefore, it
is advisable to have corn as a second crop, during the dry season so as
to avoid corn borer damages. However in areas where there have been no
widespread infestations, corn can still be planted during the 1st
season.
WEED UTILIZATION
How it’s done: Deliberately planting Ipomoea sp. (yam and its relatives)
within corn rows or allowing Ipomoa triloba, a weed species, to grow in
a manageable level (i.e. will not cause significant yield loss) in the
field.
The Principle: Corn borer population was reduced in corn plots heavily
infested with Ipomoea Triloba. I. triloba, a common weed, can host
natural enemies which prey on the borer larvae thus, significantly
reducing the infestation and possible yield reduction. Color background
providing a deterrent factor, creation of diversified environment for
the habitat of natural enemies of the major pests and provision of
mechanical barriers for insect pests are some of the possible factors
responsible for the results obtained.
BIOLOGICAL CONTROL USING TRICHOGRAMMA
How it’s done: Trichogramma, which are parasites of corn borer eggs,
can be mass produced and released into a corn field by hanging on the
corn leaves approximately 25 paper strips (containing the insects) for
every hectare per week. The insects then fly and parasitize the corn
borer eggs. The trichogramma itself dies when the said food source is
already unavailable.
The Principle: Trichogramma is a hymenopteran (a group of insects),
which specifically feeds on the eggs of lepidopterous pests (such as
corn borers, army worms, stem borers etc.) by parasitizing them.
In northern Philippines, it was shown that the inoculation with
trichogramma resulted to 90% to 95% infestation of the corn borer eggs.
These die and therefore, the corn borers are stopped even at their early
stages. The cost is minimal. Each inoculation amounts to only P50 (a
little less than US$1) per hectare per week. (MNV)
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