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Corn rootworm (Diabrotica virgifera (de l’ouest), Diabrotica barberi (du Nord))

Adult corn rootworm

Corn rootworm biology & life cycle

Two species of corn rootworm (CRW), Western and Northern, can impact both corn yield and harvestability. Both the larvae and adult stages of corn rootworm result in crop damage. Signs of infested fields include poor root formation, plants with curved stalks (goose necking) or a high proportion of lodged plants.

In the fall, adult CRW look for corn fields on which to feed and lay eggs. These small, white eggs overwinter in the soil and go through diapause (winter chilling) before they hatch. Once the soil temperatures reach 10°C, larvae emerge and feed on corn root hairs for three to four weeks. They also tunnel into the roots resulting in poor water and nutrient uptake, as well as a loss of structural support to the stalk.

Later in the season, adult rootworm feed on fresh corn silks. Severe feeding may affect pollination of sweet corn if the silks are clipped prior to seed set, resulting in a barren cob.

CRW complete only one generation per year.

Identifying Corn rootworm

Adult

Corn rootworm: Larvae

CRW larvae are cylindrical worms with a white body, brown head and 6 small legs behind the head. Fully grown larvae are 3 mm to 1.5 cm long. They emerge in late May to mid-June, and feeding continues until mid-July.

Corn rootworm: Pupae

Once larvae leave the roots, they form a small earthen cell and transform to the pupal stage, which takes one to two days. Pupae are white, delicate, resemble the beetle and are often found next to the plant base.

Adult

Corn rootworm: Adult

Adult CRW have hard shells and are roughly 6 mm long. The Western CRW is yellow with black stripes on the wing pad. The Northern CRW is pale green-yellow. First generation adults emerge in late July through early August.

Corn rootworm: Management

To effectively manage CRW, implement a multi-year plan that includes a variety of tactics, including:

  • Practice crop rotation – CRW larvae perish soon after hatching if a crop other than corn is planted in the field they inhabit.
  • In the absence of a good rotation, use a systemic insecticide seed treatment.
  • Late summer populations are usually kept under control by corn borer and earworm sprays.
  • Scout for adults during silking. Consider a foliar spray if adult populations feeding on silks exceed 10 per plant.
  • Plant seed with multiple CRW B.t. traits vs. seed with a single trait
  • Prescriptive use of soil-applied insecticides may be warranted based on field/trait history and CRW populations.
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Sources
http://www.omafra.gov.on.ca/IPM/english/sweet-corn/insects/corn-rootworm.html#advanced
https://corn.agronomy.wisc.edu/Management/pdfs/A3328.pdf

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