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October 31, 2014

Corn Earworm Already Detected from North to South in Brazil

The insect pest that has generated the most concern for Brazilian farmers over the last two years is the corn earworm (Helicoverpa armigera). The insect has cost Brazilian farmers billions of reals in control costs and lost production since its surprise discovery in western Bahia during the 2012-13 growing season. In spite of its name, damage from the insect is not confined to just corn, it can also impact soybeans and cotton production as well.

Since its discovery in western Bahia, the insect has been found in all the major soybean producing regions of Brazil. In fact, Brazilian scientists announced this week that the insect has been found in emerging soybean fields from Mato Grosso all the way south to the state of Rio Grande do Sul in far southern Brazil.

In the municipality of Primavera do Leste in southeastern Mato Grosso the pest has already been found in newly planted soybean fields. Some of the soybeans that were planted at the end of September have already been sprayed three times in an attempt to control the pest. Farmers in the region expect to make up to six insecticide applications during the growing season to control not only the corn earworm, but also other insect pests as well.

The insect causes losses by defoliating the plant, but during early vegetative growth when the plant is growing vigorously, limited defoliation can occur without a major negative impact on yield. Insect feeding is much more important during pod formation and pod filling because it can attack the pods and the developing seeds.

In a tropical climate such as central Brazil, it is very difficult to control insect pests due to the lack of cold temperatures between growing seasons. In fact, if irrigation is available, crops can be grown year round offering a continuous food source for various insect pests. That is why researchers emphasize the importance of eliminating all volunteer plants including soybeans, corn, and cotton between growing seasons as a way to help control the insect.

Additionally, safrinha corn or even cover crops such as millet can be a food source for the pest. Researchers advise farmers to be sure and eliminate all volunteer corn as well as millet cover crops in advance of soybean planting as a way to limit the spread of the insect.

The corn earworm has also been confirmed in insect traps in the state of Rio Grande do Sul in far southern Brazil. Researchers in the state have warned farmers to be alert for the insect as soon as the soybeans emerge and to take preventative action as soon as the insect is discovered.