As Corn Harvest Progresses, Watch for Damage from Western Corn Rootworm
Figure 1. Heavy rootworm damage can cause corn plants to lodge because they do not have enough roots to stand well
With silage harvest starting, I thought it would be prudent to remind folks of the risk posed to continuous corn fields by western corn rootworm. In Pennsylvania, rootworms are not a problem that you are likely to encounter in corn fields that were rotated annually with soybeans or other crops; they are a pest of fields planted with corn year after year.Â
As you get into corn fields with harvest, it would be wise to take note of lodged and goosenecked corn plants (Figure 1). While rootworms emerged as beetles from the soil in late July and early August, these plants may indicate that your field hosted large rootworm populations. And even if you planted hybrids with the newest traits, you could still see damage. If you find lodged plants, consider digging up their roots to assess the situation. While roots can regrow along the lodged stem, damage from rootworms may still be evident (Figure 2).
A few weeks ago, I visited a continuous corn field in Centre County that had lots of lodging even though the grower appears to have planted a hybrid with three transgenic traits targeting rootworm (the traits appear to have included the most recently introduced one). We still have some work to do to confirm the situation in the field, but the risk and message should be clear: rootworms can evolve resistance to all transgenic traits targeting them.
Therefore, to effectively manage rootworms in the coming years, growers and their agronomists need to honestly evaluate the performance of the traits this year and then make an informed plan for 2027 to manage this pest species. If you would like help with this challenge, get in touch with your local agronomy educator from Penn State Extension, and we can provide unbiased guidance.
If you do encounter heavy lodging caused by rootworms, report the problem to your seed dealer; they have an obligation to investigate the situation. I also recommend contacting your local Extension educator or me because we can get involved to interpret the situation and provide advice for next year. To read more about this topic, please see our factsheet on managing potential rootworm resistance to Bt.
