Corn Rootworm Levels in the Central Corn Belt - 2022

• Objective: Assess CRW populations across Illinois, Indiana, Iowa, Minnesota, South Dakota and Wisconsin.
• Locations: 438 corn and soybean field locations across Illinois, Indiana, Wisconsin, Minnesota, Iowa, and South Dakota.
• Sampling Methods:
  • Six sticky traps placed per field starting at blister stage (R2) (Figure 1).
  • Northern and western CRW beetles were counted every seven days, with traps replaced every week (Figure 2).
  • Trapping continued for six consecutive weeks by Pioneer sales professionals and agronomists.
    
    

    

    Figure 1. Placement of a new Pherocon^® AM/NB sticky trap on a corn plant (left). Arrangement of six traps in the field (right).

  • 

    Figure 2. Western corn rootworm beetle (left); northern corn rootworm beetle (right).

• Weekly average trap counts ranged from zero to 269 beetles per trap.
• 86% of fields sampled showed some level of CRW pressure.
• The highest average weekly trap counts were found in Wisconsin and Northern Illinois.

• Corn rootworm populations were characterized at four different levels for each sampling location (Table 1).
  • Zero = no beetles collected
  • Low = traps averaged <21 beetles/week
  • Moderate = traps averaged 21-50 beetles/week
  • High = traps averaged >50 beetles/week

• Western CRW was found in nearly all sampling locations across all states in the sampling area.
• Northern CRW was prevalent across most of the sampling area except for Eastern Illinois and Indiana.

• Sticky traps were put in the field at R2 and the first week’s counts were taken seven days later and continued on a weekly basis. Since the traps were placed based on crop development rather than a calendar date, traps in the southern part of the study were placed in the field earlier than traps in the northern part of the study.
• Timing of peak beetle trapping (based on weeks following R2) varied depending on geography. Locations in Indiana, Illinois, and Iowa tended to have peak beetle counts during week 1 or 2 of trapping.
• Locations in Wisconsin and Minnesota tended to have peak beetle counts occur later in trapping.

• Farmers throughout the Central Corn Belt need to be aware of CRW pressure on their farms, especially in continuous corn rotations.
• Northern CRW, and the potential for its extended diapause variant, is a greater concern in Wisconsin, Minnesota, Iowa, and South Dakota than in Illinois or Indiana.
• Farmers who are monitoring CRW beetles using sticky traps may be able to make a good population estimate after 1 to 2 weeks of trapping in central Illinois and Indiana. Farmers in the northern and western portions of this study area should trap at least 4 to 5 weeks for more accurate counts.

When using CRW beetle trapping to monitor populations:

• If traps average <21 beetles per week:
  • Low rootworm populations are anticipated next year
    • Rotate acres to another crop.
    • Plant a corn rootworm Bt corn product.
    • Plant a non-Bt rootworm product with Lumisure^® 1250 insecticide treatment OR a soil insecticide for larvae.
• If traps average 21-50 beetles per week:
  • Moderate rootworm populations are anticipated next year
    • Rotate acres to another crop.
    • Plant a corn rootworm Bt corn product.
    • Apply a soil insecticide at planting for larvae.
• If traps average >50 beetles per week:
  • High rootworm populations are anticipated next year
    • Rotate acres to another crop.
    • Apply foliar insecticide in the current year to control beetles prior to egg-laying and use a corn rootworm Bt corn product or soil-applied insecticide the following year.
• Pioneer and university research suggests that continuous, uninterrupted use of the same corn rootworm Bt technology can lead to reduced product efficacy against these insects.
• To maintain efficacy of Bt corn rootworm products, it is essential to develop a rootworm management plan that:
  • Breaks the cycle
  • Manages populations
  • Protects the Bt trait
• Please contact your Pioneer sales professional for more information.