Insecticides can increase pest damage
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CTA. 1992. Insecticides can increase pest damage. Spore 38. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/45718
Groundnut farmers in India apply so much insecticide that they end up inducing pest outbreaks. Their counterparts in Africa rarely use chemical sprays, and their crops suffer less damage from pests. Researchers at the International Crops Research...
Groundnut farmers in India apply so much insecticide that they end up inducing pest outbreaks. Their counterparts in Africa rarely use chemical sprays, and their crops suffer less damage from pests. Researchers at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India have been looking at why African groundnut crops suffer little from pest damage. It seems that because Indian farmers spray at least seven times in the season the natural enemies of the pests are just not able to recolonize the crops as quickly as the pest. When the groundnut crop is quite young it is attacked by jassids and thrips. These cause only superficial damage, which results in no crop loss. But the farmers are encouraged to spray against the pest because the crop begins to look untidy and yellow. However, the spray not only kills the jassids and thrips but also the parasites of the groundnut leaf miner, the next major pest to appear. When ICRISAT withheld sprays in their fields they found that 70-80% of the miners were parasitized and, in consequence they caused less crop damage. But if the parasites are killed, the miner can be very destructive. Later in the season the armyworm appears and starts to eat the leaves. Farmers do not realize that these pests can eat up to half the leaves without having any affect on yield. Even when farmers do spray, the costs incurred are not recovered by the increased yield. The last important pest of the season is Heliothis or pod borer. By this time any beneficial insects have been killed by all the previous spraying. ICRISAT plant breeders have now bred groundnut lines that are resistant to jassids and thrips. ICRISAT hopes that farmers using these new lines will not use sprays early in the season. If sprays are withheld at that time there is usually no need to spray later on, because the beneficial insects have been able to increase their populations. ICRISAT researchers hope that African farmers will be able to benefit from the results of these findings. ICRISAT Patancheru PO Andhra Pradesh 502 324 INDIA