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December 14, 2012

A New Pest Called "Cotton Worm" Found in Brazilian Soy Fields

Soybean farmers in several Brazilian states have discovered a new insect attacking their newly planted soybean fields. They are calling it the "cotton worm" since it is a common pest where cotton is grown, but rarely if ever seen attacking soybeans. This new pest has been found in the states of Mato Grosso, Mato Grosso do Sul, Goias, Minas Gerais, and Sao Paulo. If left unchecked, this leaf eating caterpillar has the capacity to defoliate the crop within five days.

The worm is being found in areas where cotton is not grown and agronomists are having a hard time explaining why this pest appeared in such numbers this growing season. It's possible that the insect is just migrating from one region to another, but that seems to be too simple of an explanation especially since the worm has been found in a wide geographic region.

An agronomist in the state of Sao Paulo theorizes that the increase of this pest is potentially connected to the increased use of Bt corn hybrids. Three quarters of the corn grown in Sao Paulo is Bt corn which does not require insecticide applications to control insects. The resulting decrease use of insecticides has allowed more rare species of insects to multiply freely and then to migrate into soybean fields. Scientists continue to examine the situation and additional possible explanations may be forthcoming.

Farmers with this problem are being forced to make one or possibly two additional insecticide applications at a cost of approximately R$ 60 per hectare for each application depending on the chemical used. The cost of each additional application is equivalent to approximately one sack of soybeans per hectare or about one bushel per acre.

One of the problems with this new pest is that farmers are not allowed to use insecticides that have successfully controlled the insect in cotton fields if the chemical is not registered for use in soybeans. Therefore, farmers are using insecticides registered for soybeans not knowing if it will do an adequate job in controlling the insect.

In severe cases may have to do 4-5 applications to control all the various insects.