Managing Corn Rootworm Populations

Growers reduce risk from corn rootworm damage primarily through one of the following methods or a combination thereof:

  • Regular crop rotation to soybeans or another non-host crop to break the corn rootworm life cycle. Periodic rotation provides a number of benefits in addition to effective corn rootworm control;
  • Planting dual mode-of-action (pyramided) Bt-trait products, such as  Genuity® Smartstax® RIB Complete™ – that provides both above- and below-ground protection against corn rootworm;
  • Planting hybrids that do not provide Bt protection with soil- applied insecticides at planting to manage larvae; and
  • Use of crop scouting and thresholds for foliar applied insecticides to reduce adult corn rootworm population densities.

Crop Rotation to Soybeans or Another Non-Host Crop

Farmers widely use crop rotation to a non-host crop as a key management strategy for control of corn rootworm throughout the Corn Belt. Since corn rootworm larvae need to feed on corn roots to survive, crop rotation ensures that eggs laid in a corn field being rotated the next year will hatch in a field planted to a non-host that larvae cannot feed upon – breaking the pest’s life cycle and effectively eliminating corn rootworm in the field in most areas.

Crop rotation is a cultural practice that is widely recommended by academics and seed company agronomists for effective management of corn rootworm. However, in certain areas of the Corn Belt corn rootworm species have adapted to crop rotation through extended diapause, like the northern corn rootworm, or by egg laying in non-host crops such as soybean, like the soybean variant of the western corn rootworm. As a consequence, in some areas the first-year corn following a rotational crop may still be at risk from corn rootworm. Especially in geographies where “rotation resistant” western corn rootworm populations exist, crop rotation should be used as one component of an Integrated Pest Management (IPM) strategy to reduce plant damage from corn rootworm.

Dual Mode-of-Action Trait Products

Bt (Bacillus thuringiensis) proteins have long been used as topical sprays in conventional and organic agriculture because they are effective and can be used safely. Crops that carry the Bt trait allow farmers to protect their crops while eliminating or significantly decreasing the number of pesticides sprays.

Monsanto and other trait providers developed insect-protected plants using Bt in order to protect the yield potential of plants and significantly decrease the need for chemical pesticide applications. Today, many U.S. corn farmers use Bt trait technologies with dual modes of action to manage corn rootworm. 

Rootworm-protected crops utilize a Bt trait to protect the corn’s root system. Dual mode-of-action products such as Genuity Smartstax RIB Complete express two unique Bt proteins to manage corn rootworm.

Monsanto’s rootworm-protected corn products will sustain less damage from corn rootworm compared to corn without a Bt trait. However, they do not provide control for all insect pests that target the crop. Therefore, it is important to understand that, in some cases, infestations of economically important insects may occur and require additional control measures.

The best way for farmers to preserve the benefits and insect protection of Bt technology is to incorporate IPM practices and effectively implement required Insect Resistance Management (IRM) plans.  IRM practices are used to decrease the likelihood of insects developing the ability to survive the ingestion of insect-protected transgenic crops. Every farmer who utilizes Monsanto’s Bt corn products must comply with licensing terms and must follow IRM plan as required by the U.S. Environmental Protection Agency.

Learn more about refuge requirements.

Soil- or Foliar Applied Insecticide Treatments

In areas where acres are planted to continuous corn, soil-applied insecticides have served as important tools in combating corn rootworm. These insecticides are applied to the soil at planting to control larvae. or applied to the plant during the growing season to control adults and prevent them from laying eggs that turn into larvae that damage the corn roots the following season.

While insecticides are reasonably effective most years, their effectiveness varies depending on a number of factors, especially environmental conditions. Insecticide efficacy can be highly influenced by the weather. For example, properly timed rain is needed for the successful functioning of the active ingredients of a soil-applied insecticide applied at planting but too much rain can reduce their effectiveness. In fields with high adult corn rootworm pressure, farmers can minimize the potential for corn rootworm populations to develop resistance to common foliar insecticide treatments by rotating between insecticides with different modes of action. In extreme situations, combining two or more insecticide applications with different modes of action for corn rootworm control can be utilized to knock down the high populations. Especially for foliar insecticides applied for the purpose of managing adult beetles, applications should be based on established spray thresholds triggered by information obtained through regular crop scouting.  Prophylactic application of insecticides should be avoided whenever possible.