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April 2, 2014

Corn Earworm Damage in Bahia less than Feared

At the start of the 2013/14 growing season many farmers in western Bahia were almost in a panic concerning the corn earworm. Bahia was the Brazilian state where the worms were first identified during the 2012/13 growing season and many soybean and cotton farmers in the state suffered significant losses due to the pest. Nearly everyone was predicting that the 2013/14 growing season would be worse and numerous articles and special reports predicted dire consequences due to the corn earworm.

At the same time that the popular press was predicting a disaster, many entomologists tried to calm farmer’s fears by stating that they were confident that the pest could be controlled in Brazil just like it had been controlled successfully in other countries. In the end, the entomologists were correct and the damage caused by the corn earworm (Helicoverpa armigera) in Brazil ended up being much less than what farmers had feared.

By most accounts, the attacks from the corn earworm in western Bahia were estimated to be 60% less than last year. Scientists attribute the lower insect pressure to a variety of factors including: more suitable weather, biological control, more targeted insecticide usage, and the use of integrated pest management on the part of the farmers.

During the first year the worm was identified in the fields of Bahia, farmers panicked and they applied nearly any insecticide they could get their hands on not knowing if it would work or not. It turned out that a lot of chemicals did not work and farmers were just spending money needlessly.

This growing season everyone was much more focused on monitoring the insect levels and only apply chemicals known to be effective after the insect populations reached an economic threshold. These monitoring programs were in in place last growing season due to the newness of the pest.

Many farmers also used integrated pest management techniques to help control the insect. At the heart of integrated pest management is the use natural enemies to control pests. Some farmers applied a virus instead of chemicals which allowed more natural enemies such as spiders and wasps to flourish and feast on the moth’s eggs. In fact the damage from the corn earworm was less in areas where fewer chemicals were applied.

In Bahia, where the worm was first identified last growing season, producers spent R$ 600 million on insecticides for their cotton and soybean crops during the 2013/14 growing season, which was 50% less than last year. Even though they used fewer insecticides this growing season, they had better success in controlling the pest.

Scientists from Embrapa are first to acknowledge that there is a lot about the pest that they cannot explain. Even though the insect has been identified in nearly every region of Brazil where row crops are grown, they cannot explain why insect numbers remained below the economic threshold in most areas. They also cautioned that farmers and scientists should not get over confident just because they appear to have been successful in controlling the pest this growing season.