8 December 2001
WHY FARMERS DON'T NEED BT-CORN: CULTURAL MANAGEMENT OF CORN BORER
Masipag News & Views
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:
How itís 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 ñ 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 ñ5th instar, when they start boring holes into the corn
stem, which is considered most destructive to the corn.
*FALLOW CROPPING OR CROP ROTATION
How itís 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 pestís life cycle and thus its proliferation.
How itís 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.
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.
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.
How itís 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 itís 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)
[Masipag News & Views is an occasional information release of the Farmer Scientist Partnership for Development (MASIPAG). This report, in whole or in part, could be freely published.]
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Los Banos, Laguna
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