About the Southern Cornstalk Borer
Reproduction and Life Cycle
The southern cornstalk borer will spend the winter as larvae in cornstalks near the base, or from within taproots. They will change to pupae around April. The adults emerge about 10 days later. They immediately begin mating and the females will lay their eggs during the evening on the upper surface of leaves. The eggs are first laid in clusters of about 20 with the eggs overlapping one another similar to that of shingles. As the female becomes older, she will lay clusters with fewer and fewer eggs until she is only laying them individually. The eggs take about 9 days to hatch. The newly hatched larvae will find their way to the plants whorl and begin feeding, spinning a silk thread wherever they go. They develop through 5 to 6 instars. Once they reach the third instar, they will work their way down the stalk to the base. It will take them an average of 30 days to complete all instars. They pupate in the stalk. This pest has a total of 2 generations each year.
Southern Cornstalk Borer Identification and Habitat
The adult southern cornstalk borer is a crambid snout moth. They are white to straw coloured with hind wings darker in colour than the forewings. The wingspan ranges from 15 to 40mm in length with the females having a slightly larger span than the males. The eggs are oval, flattened and are about 1.6mm in length and 1mm in width. They begin as a dull white, later changing to a yellow-orange with 3 orange-red lines that run crosswise. Upon hatching, the larvae are about 1.5mm, but will grow to be 25mm once they reach full maturity. They start out as a brownish colour with a head that is black and the body segments grow darker towards the rear. As they mature, their appearance will be dependent on what season they are in. The winter generation is pale yellow, still with a dark coloured head. They have very light spots that are hard to see on their back and tend to appear thicker than the summer generation. The larvae in the summer have a yellow-brown head, are a milky white, and have spots that are darker than the winter generation that run along their back. Each spot has a dark bristle attached to it. The puparium is 22mm in length and starts off as a similar colour to its larval form, but will eventually adjust to a red-brown.
This pest is most commonly found in the southeastern states, reaching as far as Ohio and Maryland in the northern direction and to New Mexico and Kansas in the western direction. They feed on corn, sugarcane, sorghum, broomcorn, grain, panic grass, and Johnson grass. The larvae will eat from inside the plant whorl. When the leaves of infested and plants begin to unfold, holes in uneven rows can be seen. Sometimes the caterpillars also eat the central vein of leaves and can destroy the growing point of the leaf whorls. Mature larvae will eat their way into the plants stalk, especially on the lower section of the plant directly above the soils surface. This can damage the root system and stunt the plant as it restricts water and nutrient intake from the ground. Unfortunately this pest is not often noticed until major damage to the stalk has already been caused.
Southern Cornstalk Borer Management and Control Methods
To help suppress the southern cornstalk borer’s population, during the fall plan to disc your corn fields to help kill any larvae that were hoping to overwinter in the stalks. This is effective because this pest will not be able to survive if the stalk is uprooted and exposed during the winter. Practice crop rotation so you do not have corn planted 2 years in a row in the same field as this can increase their population. However, it is important to note that having satisfactory control is often dependent on using an integrated management system that includes the use of both cultural and chemical methods.
To control this pest with insecticides, some chemicals that have had success in corn fields are cyhalothrin, esfenvalerate, and permethrin. Cyhalothrin and esfenvalerate should be applied at least 21 days before harvest. You can also use endrin, aldrin, heptachlor, and dieldrin. Whether it is a spray or granulated application, the effectiveness is quite similar. These chemicals do show better results if applied during corn emergence. Be sure to carefully read the label for cautions and proper application. It is extremely important to never spray on days that are windy. After applying insecticides, it is important to irrigate sprayed area to increase the insect control. That being said, a large rainfall or irrigation soon after the application can reduce the concentration insecticides.
Latin / Alternative Southern Cornstalk Borer Names