While there are traits and products to help you protect your corn crop against rootworm, you still need to manage against the pest and that means knowing about the larvae and adult beetle populations in your fields. Scouting to keep tabs on those populations is essential to protecting your corn crop against rootworm damage.
"Wet soils and cooler temperatures challenged the growth of corn early this year. These conditions may have also controlled early-hatching larvae by reducing their food source and saturating the soils," says Clint Pilcher, a DuPont Pioneer insect resistance management expert. "Regardless, growers should still scout their fields to check on the effectiveness of their control program and plan accordingly if they have severe problems."
The goal is to break the rootworm cycle and manage the population. Options for corn rootworm include rotating crops, alternating traits or stacks within planted corn hybrids, enhancing control with insecticide seed treatments and soil-applied insecticides, or spraying adult beetles during silking.
In-season scouting--check fields for adult corn rootworm beetles in July and August
Adult corn rootworm beetles impact grain fill by chewing off the green silks, causing spotty pollination later in the season. The larval stage, however, is the most damaging and impacts yield by feeding on corn roots. One way to determine the current level of rootworm pressure and the potential for future threats is to scout your fields for adult beetles in July and August. Scouting helps determine whether to spray the current crop and limit the potential for population outbreaks the next crop season. When scouting, look for lodged plants with heavy damage on the root system.
To ensure that spraying rootworm beetles will pay off, determine that the critical population threshold has been met before using an insecticide. This guideline is location specific, so consult your local agronomist or seed sales professional for corn rootworm beetle threshold levels in your area. If the threshold is met, you can apply a timely foliar insecticide to control the egg-laying adult population.
Planning for next year—think ahead about controlling corn rootworm for next crop
After following these recommendations, it's important to begin thinking ahead about controlling corn rootworm for the next crop, which includes following programs that preserve the rootworm control traits in corn hybrids for the long term.~~~PAGE_BREAK_HERE~~~
"The best thing growers can do to help eliminate rootworm pressure is to rotate the field to another crop, such as soybeans," Pilcher states. "Corn rootworms love corn-on-corn, so anything growers can do to break that cycle is best."
If there is no opportunity to rotate a field to another crop, consider a product with multiple modes of action in corn rootworm-resistant traits, such as Optimum AcreMax XTreme insect protection, says Pilcher. Research has shown that an integrated refuge, which is offered in Optimum AcreMax seed corn products, is best for insect resistance management of corn rootworms. If the same mode of action has been continually used to manage rootworm pressure, consider using another trait or using pyramid products to help break the cycle.
Should you use a soil-applied insecticide on corn that has a rootworm resistance trait?
Another preseason management option, if you are planting continuous corn-on-corn in regions where there is extremely heavy rootworm pressure, is to use a soil-applied insecticide in combination with a corn hybrid that has the genetic resistance trait. Optimum AcreMax corn hybrids have the trait, but Pioneer does not make this a standard recommendation.
"Corn rootworms are becoming more and more difficult to manage, so we as an industry need to be very aware of the practices we use," says Pilcher. "If we want to use these practices and products long-term, they need to be managed properly." To keep insect control solutions effective for years to come, rotating corn hybrids that have different Bt events or rotating crops such as corn with soybeans are the best options.
To keep insect control tools effective for the future, rotating corn hybrids that have different Bt rootworm events, and rotating corn with soybeans, are best bets
If using a blended, in-bag refuge product is not an option for you, using a structured refuge is required in combination with certain Bt-rootworm corn hybrids. Practicing good stewardship like planting a refuge is vital in helping maintain a population of corn pests that are susceptible to resistance traits. In the long-term this will help preserve the viability of insect protection for in-plant traits.
"When it comes to keeping insect control solutions for years to come, rotating products or crops are the best options," sums up Pilcher. "You can also work with your local seed company sales professional or local agronomist to develop a long-term corn rootworm management plan that fits your acres."