Selecting the right hybrids is key to minimizing yield lost to insects.
Hybrids differ in tolerance to corn borers (Bt) for several reasons. During reproduction, egg-laying moths are attracted to the largest corn plants. Hybrids with Late Health and Early Health Genetic Families have relatively aggressive early-season growth, especially during cool, wet weather, which makes them attractive to egg-laying moths. When using hybrids with fast-growing genetic families, plant them first and use Bt to reduce the risk of corn borer damage to protect the yield benefit of early planting.
Second-generation corn borers prefer the latest-planted, most-immature corn. The Eastern genetic type takes the largest yield hit from second-generation corn borers because it flowers late for its maturity and stays green later in the fall. For this reason, Eastern types provide the highest financial return on investment with Bt technology.
Southern-type genetics have unusually skinny shanks that quickly break when invaded by corn borers, causing dropped ears. This is aggravated by the fact that hybrids with the Southern Genetic Family make the largest, heaviest ears. Southern genetic types have a strong response to Bt with a large reduction in dropped ears. Western genetics have the best native tolerance to corn borers, with the fattest shank attachment for ear retention, but are the least responsive to Bt, making them the best choice for refuge acres.
The girthy-ear High Yield female crossed with the long-ear Southern male is the highest yielding of all genetic types, if nitrogen is applied aggressively. Protect the high-yield potential of this style hybrid and your nitrogen investment with Bt. Over the last five years and countless plots per year, Bt delivers additional bushels per acre across the entire Corn Belt.
With the registration of corn rootworm (CRW) technology to combat this serious insect pest, the use of dangerous corn rootworm insecticides can be avoided. When deciding to use this technology, consider your rotation, the corn rootworm pressure in your area, your soil type and the type of genetics you intend to plant.
Because rootworm adults lay their eggs in cornfields, rotation has traditionally controlled this pest. Corn-on-corn fields have historically been treated with a corn rootworm insecticide. CRW corn is a direct substitute for insecticide on these acres.
These destructive pests are now flying out of cornfields and laying their eggs in soybean fields. If the soybean field is rotated to corn the next season, a rootworm larvae population could be waiting in the field to attack the emerging corn crop. While this phenomenon is limited geographically, the area is expanding. First discovered in 1992, it is now a problem on approximately 10 million acres in Illinois, Indiana, Michigan, Ohio, southern Wisconsin and eastern Iowa. In these areas, CRW corn can reduce your risk of corn rootworm damage.
Populations of this pest in southern Minnesota, southern South Dakota and northwest Iowa have reacted to corn and soybean rotations by delaying egg hatch until two winters have passed. This strain of corn rootworm is called the diapause strain. By delaying hatch until corn is planted in the field again, larvae then have a suitable food source. You can avoid this risk by using CRW corn.
Root lodging problems are more likely with better water-holding-capacity soil types. The corn plant always takes the easiest route. If plenty of soil moisture is available, the plant makes top growth at the expense of root development, and therefore becomes prone to root lodging. The black, high-organic-matter soil types of South Dakota, Iowa, Minnesota and Illinois are the most prone to root lodging and have the best response to CRW corn.
There is also a pronounced genetic family influence on corn rootworm damage. The Northern, Late Health, Early Health, Eastern and Western Genetic Families all make hybrids with poor roots and show a significant response to CRW corn. Hybrids with the High Yield Genetic Family have the best roots and do not have the root lodging issues other genetic families experience.
- While soil-applied insecticides are effective most years, their effectiveness varies from year to year, depending on environmental conditions.
- Properly timed rain is needed for the chemistry to work successfully in the soil, and too much rain can reduce their effectiveness by leaching the insecticide below the rooting zone.
- If conditions are too dry, the efficacy of insecticides is diminished because some soil-applied insecticides need moisture for activation.
- With CRW corn, the active ingredient is in the root at the point where the rootworm is feeding. This leads to improved efficacy, which adds great value to corn-after-corn acres.