Field Guide     Pest Management     Southern Corn Rootworm

Southern Corn Rootworm

CROPS IMPACTED: cucumbers, corn, soy, alfalfa

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Family: Chrysomelidae

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About the Southern Corn Rootworm

Reproduction and Life Cycle

The southern corn rootworm overwinters as a beetle, often in a vegetative cover or in the ground by plants that have not yet been killed by the frost. In early spring, the adults will surface and begin laying eggs on the soils surface, typically at the base of plants. A female can lay up to 500 eggs in their lifetime, and will lay each egg individually or in clusters of about 20 to 30. The eggs take approximately 7 to 10 days to hatch. The larvae will then begin feeding, usually for about 3 to 6 weeks, going through 3 instars. At this point, they will pupate at a plants base under the soil. Within 14 days the adults will emerge; males often emerge before females. They will immediately begin mating, and continue to feed for another 14 days before they lay their eggs. Once a female lays her eggs, she will die soon after. Depending on climate, the southern corn rootworm can have up to 3 generations per year.

Southern Corn Rootworm Identification and Habitat

Identification

The adult southern corn rootworm is 5 to 9mm long. The beetle is a bright yellow-green and has a black head, antennae, and legs. They typically have 11 black spots on their back. The egg is a light yellow, oval in shape and a short 0.6mm in length. The larvae on average are about 8mm long, sometimes growing to be as long as 15mm when they are fully developed. Their body is pale yellow, slightly wrinkled and has 6 small brown legs. When they enter the pupa stage of development, they range from white to yellow, are partially translucent and are around 6mm in length.

Habitat

The corn rootworm is fairly common throughout North America east of the Rocky Mountains. It tends to populate the southern states the most. The larvae feed on plant roots, often corn, grass crops, cucumber, or other squash types. They have been recorded to feed off of more than 280 different plant types. This rootworm tends to prefer wet soil and will cause the most damage to corn during spring seasons that are cool and damp. They are likely to infest fields that are no-till, or after a crop of winter legumes that were turned under. The adults and larvae both feed off of the crops; however, the larvae are more harmful. The larvae will eat away at the growing points of the plant, usually making round holes that destroy the terminal blades. Once the roots mature further in the season, the larvae may continue feeding there, which allows the plant to be uprooted easily during wind or rain. Additionally, southern corn rootworms will spread the wilt bacteria to the plant it feeds on, which causes extensive damage to the plant. The adults eat every part of a corn plant, and also have the ability to spread the bacteria.

Southern Corn Rootworm Management and Control Methods

Cultural Control

To control southern corn rootworm populations, plan to plow or disk early, typically a month before planting your seed; this can discourage the rootworm from laying their eggs in the ground. Also, practice recommended agronomy steps to ensure plants have vigor and can tolerate some pest damage, or use resistant corn varieties that can also tolerate the rootworm. They also have numerous natural enemies that can assist with control, such as parasites, nematodes, and certain predators like birds. Crop rotation can be an additional aid. However, it is important to note that having satisfactory control over the rootworms population is dependent on using an integrated management system that includes the use of cultural and chemical methods.

Chemical Control

Granular pesticides applied at-planting have proven to be quite effective in controlling the southern corn rootworm. Active insecticide ingredients: carbofuran (Furadan 4F), chlorpyrifos (Lorsban 15G), Tebupirimfos plus cyfluthrin (Aztex 2.1G), Tefluthrin (Force 3G), and Terbufos (Counter 20CR). If you are looking to control the adults (in beetle form), use chemicals such as carbaryl, malathion, and methyl parathion. Be sure to carefully read the label for cautions and proper application. It is extremely important to never spray on days that are windy.

Latin / Alternative Southern Corn Rootworm Names

  • - Diabrotica undecimpunctata
  • - Spotted cucumber beetle

Sources

http://ipm.ncsu.edu/AG271/corn_sorghum/southern_corn_rootworm.html

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1029338910&topicorder=4&maxto=11