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Northern Corn Rootworm Developing Resistance to Bt Traits in North Dakota

Apr 16, 2019

Agronomy, Crop Management, Grain, Market Update, Soybean, Technology

The USDA estimates that US farmers lose more than one billion dollars annually in the fight against corn rootworm (CRW), and because the insect is adapting to our current crop rotations, producers may need to make changes to their control strategies, as well. Upon seeing high levels of rootworm damage, Arthur Companies helped North Dakota State University (NDSU) line up plots in Arthur and Page, ND, to investigate. Knowing the insect and its biology, we can implement changes to more effectively prevent and control corn rootworm.

Lifecycle: Egg, Larva, Pupa, and Adult

  1. Egg: Eggs are laid on corn roots in late summer and spend the winter as eggs in the soil.
  2. Larvae: Hatching takes place late May through June. The larvae feed by pruning developing corn roots, affecting moisture and nutrient uptake as well as standability. Damage is more pronounced when soil conditions are dry.
  3. Pupa: During the pupal stage, larvae remain dormant as they transition into adult beetles.
  4. Adult: Secondary damage occurs as adult beetles emerge from the soil in mid-July. Foraging adults feed on leaves, pollen, and silks. High populations can hinder pollination.

Corn Roots with Rootworm Larvae

Know Your Enemy

If there is not a suitable host within inches of the larva when it hatches, starvation occurs. This is why crop rotation has allowed producers to effectively control CRW. In continuous corn production, Bt traits have been heavily relied on and thus far effective. However, because of their low-dosage, the CRW Bt protein models have been less resilient. The feeding larvae gets a low dosage that makes the rootworms sick rather than actively killing entire populations. Very similar to sublethal doses of herbicides speeding the weed-resistance building process.

The results of the research by Drs. Veronica Calles-Torrez and Jan Knodel at North Dakota State University found that rootworms examined on the Arthur and Page plots have developed resistance to the two most widely used Bt proteins (brand names Yieldgard® and Herculex®), and to a lesser extent, the combination of Bt proteins in SmartStax®, are also becoming less effective.

Corn Root with Rootworm damage

This is the first documentation of Northern Corn Rootworm protein resistance anywhere. Similar issues have been found in Western Corn Rootworm in Iowa and South Dakota.

Research conducted at the University of Minnesota has also found widespread instances of extended diapause (a delayed egg hatch that extends into the following summer) in Northern Corn Rootworm across Minnesota. This delay is a perfect adaptation to the popular corn – soy – corn rotation.

Monitor to Minimize Loss

Scouting remains the most effective tool in the fight against CRW. And because knowing what to look for and what economic threshold a farm can withstand can be difficult, especially in a continuous corn operation, Arthur’s agronomy team is only a phone call away.

Corn Field with Corn Rootworm

In most cases, no significant changes are needed, and an Arthur agronomist can help determine the economic and infestation thresholds a farm can withstand.

Arthur Companies will be doing plot work and trapping for corn rootworm and European Corn Borer this season and will share those results on the blog.

To read NDSU’s extensive corn rootworm research by Drs. Jan Knodel and Veronica Calles-Torrez, please visit the university’s website here.