Threat Overview
- Bt-resistant Corn Rootworm (CRW) is a significant pest in Ontario, causing up to 50% yield loss in cornfields.
- Resistance to Bt hybrids has been identified in regions like Huron, Perth, and Durham counties.
- Ontario’s CRW situation mirrors early resistance trends observed in U.S. cornfields.
Identification
- Plant Symptoms:
- Goosenecked corn due to poor root systems from larval feeding.
- Small or clubbed roots with visible pruning, tunneling, and damage (June–August).
- Adult Beetles:
- Feeding on leaves, pollen, and silk.
- Presence of one beetle per plant during August–September signals high risk for the following year.
- Beetle Types:
- Northern CRW (green).
- Western CRW (black and yellow striped).
Conditions Favorable for CRW Proliferation
- Three or more years of continuous corn production.
- Repeated use of Bt-rootworm hybrids.
- Fields with volunteer corn growth from the previous year.
- Fine-textured soils have higher risk but all soil types are vulnerable.
Control Measures
- Crop Rotation:
- Rotate out of corn to disrupt the CRW lifecycle and prevent resistance.
- Non-Bt Hybrids:
- Use non-rootworm Bt hybrids with additional root protection (e.g., soil insecticides or seed treatments).
- Biological Control:
- Employ soil-applied bio-control nematodes (trialed in Ontario in 2021).
- Active Scouting:
- Monitor for root damage in July and adult beetles in late summer.
Important Notes
- Switching between Bt hybrids will not mitigate resistance.
- High-risk fields are those with three consecutive years of corn planting; two years presents moderate risk.
- Early action and integrated pest management are crucial to minimizing losses.
Next Steps for Farmers
- Regularly scout fields for signs of CRW activity and report damage to seed providers and authorities.
- Diversify crop rotation to reduce CRW populations and resistance risks.
- Stay informed about new control methods and resistance management practices.
By taking these measures, Ontario farmers can help safeguard yields and curb the spread of Bt-resistant Corn Rootworm.
