Southwestern Corn Borer

Diatraea grandiosella

Southwestern corn borer on a corn leaf
Southwestern corn borer on a corn leaf. Photo courtesy of Frank Peairs. Licensed under CC BY 3.0.
The southwestern corn borer is similar in behavior to European Corn Borer and can cause significant yield loss in corn and sorghum. It has 2-3 generations per year. It's geographic range is limited to areas with average January temperatures of at least 19 degrees F.
Larvae are white or grey in color with a brown head. Summer generations have distinct dark spots, while winter generations may be nearly solid white. They range in length up to 1".
Summer generation southwestern corn borer on a corn leaf
Summer generation southwestern corn borer on a corn leaf. Photo courtesy of Alton N. Sparks, Jr. Licensed under CC BY 3.0.
Adult moths are white or tan in color with fine brown lines on the wings.
Southwestern corn borer adult moth
Southwestern corn borer adult moth. Photo courtesy of Frank Peairs. Licensed under CC BY 3.0.
First generation southwestern corn borers feed in the whorl for the first few instars, then bore into the stalk. The stalk boring reduces nutrient uptake into the plant, reducing yield. It may also damage the growing point of the plant, killing it. Later generations may feed directly on the ear before boring into the stalk. Mature southwestern corn borers will bore out a region at the base of the plant, greatly weakening it and making it prone to lodging and subsequent yield loss.
Southwestern corn borer larvae can be controlled by several insecticides. Timing is critical since the larvae cannot be controlled once they are protected in the stalk. Always read and follow all label instructions.
Many Bt traits provide protection against southwestern corn borer.