Western and northern corn rootworms have a history of adapting to and overcoming control practices, which has increased the complexity and difficulty of successfully managing these pests. Insecticide resistance has been documented in populations of western corn rootworm, both to soil applications for larva control and foliar applications for adult control. Crop rotation was long an effective and widely used management strategy; however, both species have developed adaptations that have challenged the effectiveness of soybean crop rotation in many areas.
A population of western corn rootworm, dubbed the “eastern variant,” developed the ability to defeat 2-year corn-soybean rotations by laying its eggs in soybean fields rather than corn fields. Larvae hatch the following spring into the corn year of the rotation, allowing their survival. First discovered in eastern Illinois in 1987, this population quickly spread to Indiana and eventually moved across the entire state to Ohio and Michigan counties. It also moved north and west in Illinois (Cook et al., 2005) and can now be found in southern Wisconsin and eastern Iowa as well (Dunbar and Gassmann, 2013; Prasifka et al., 2006).
Northern corn rootworm populations defeated rotation by a different adaptive mechanism – extended diapause. Diapause is a winter dormancy stage of rootworm eggs. Eggs exhibiting extended diapause remain viable in the soil for 2 or more years before hatching, allowing the insect population to survive until corn returns to the rotation. First documented in the 1920s, rotation-resistant northern corn rootworms can now be found throughout much of the northern Corn Belt. Extended diapause can last up to 4 years and has shown adaptability to rotation patterns over time; i.e., fields with corn every other year have a relatively high percentage of eggs that hatch in the second year, and fields with corn every third year tend to have more eggs that hatch the third year, etc. (Levine et al., 1992).
The potential for insect pest populations to become resistant to Bt was recognized before Bt corn entered the market, with the first instance reported in 1985 (McGaughey, 1985). To reduce the probability of insects developing resistance to Bt corn, the Environmental Protection Agency (EPA) mandated certain provisions on the use of Bt corn products. One of the most important EPA requirements is that growers implement an IRM (insect resistance management) program, which includes planting an insect refuge.
The goal of a refuge is to ensure that susceptible insects are available in sufficient numbers to mate with any resistant survivors from Bt fields. Susceptible × resistant matings dilute resistance in the population and reduce the probability of building up resistant insect populations. To be effective, the refuge must be large enough and close enough to the Bt field and be planted with a similar hybrid under similar management practices.
There are 2 types of refuge products for Pioneer brand hybrids with Bt traits: integrated and structured. Some Bt products have an integrated refuge with refuge seed blended in the bag, while other Bt products require a structured refuge. A structured refuge requires a grower to plant a portion of a field with another product that does not contain the insect-control traits of the Bt product.
AM1 - Optimum® AcreMax® 1 Insect Protection System with an integrated corn rootworm refuge solution includes HXX, LL, RR2. Optimum AcreMax 1 products contain the LibertyLink® gene and can be sprayed with Liberty® herbicide. The required corn borer refuge can be planted up to half a mile away.
PIONEER ® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.