September 2, 2020
The severe corn lodging and structural damage that occurred in parts of the Midwest this month was unprecedented and extremely demoralizing.
Managing damaged fields for the 2021 growing season will require reviewing options for management of the existing crop, whether to harvest or not, as well as reviewing tactics for the 2021 production season.
One major concern will be management of the corn rootworm complex, when adult sampling in 2020 was disrupted.
I plan on planting soybeans in the damaged fields in 2021. Should I be concerned with corn rootworms?
Planting the field to soybeans will result in controlling the corn rootworm larvae in 2021. However, keep in mind that volunteer corn will most likely be quite common in these fields in 2021. Management steps should be taken to limit the volunteer corn as much as possible as it can serve as a host for developing larvae and can be attractive to adults in the late summer. For more information on managing volunteer corn, read the Spotlight Managing Volunteer Corn in Soybeans.
I plan on planting the damaged fields to corn in 2021 and I don’t have adult beetle counts from before the storm or plan on taking any before harvest. What are my options for 2021?
If the corn rootworm adult population is unknown and corn is to be planted in the field, consider selecting a corn product with below-ground traits for the control of corn rootworm, such as those that contain SmartStax® Technology. If selecting a corn product without below-ground traits, consider applying an insecticide at planting that is labeled to control corn rootworm and is applied at the full labeled rate.
I am considering planting winter wheat or a cover crop of winter rye. What is the potential for corn rootworm injury to either of those crops?
None. Corn is the only agronomic host, so planting either of these crops will not result in injury.
I don’t plan on harvesting the crop and will use tillage to incorporate the residue. Will the tillage have an impact on the corn rootworm eggs in the soil?
Tillage will not have any impact on egg survival.
I am considering applying an insecticide to the field to kill the adults I see still feeding on the silks. Will this reduce the risk of injury if I plant corn next year?
It is unlikely to influence next year’s population as females may have already deposited eggs at this point in the season.
If I plant corn next year, can I use larval sampling next year to determine if I have a damaging population of corn rootworms?
In some situations, larval sampling can be used to determine the potential for economic injury, with a working threshold of two or more larvae per plant based on a 10-plant sample per field. However, this is considered a rescue treatment and by the time the insecticide is applied (either at lay-by cultivation or through overhead irrigation) and reaches the target zone, significant injury may have already occurred.
I did not observe any corn rootworm adults in my damaged corn field prior to the storm, will they now move into the field and lay eggs resulting in injury next year?
If adults were not found in the field before the storm and the silks had browned and begun to dry down, it is unlikely that the corn would be attractive to egg laying females now, as they prefer green silks. However, if your field was planted later or a later maturity was used and the silks are still somewhat green after the storm, the field may attract egg laying females.
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