Corn growers in Nebraska and throughout the western Corn Belt might have noticed an uptick of western corn rootworm beetles emerging later into the season than normal this year — into August and September in some cases.
"Adult corn rootworm beetles generally emerge from early to mid-July and are found in cornfields throughout August and September," says Troy Bauer, BASF field technical representative. "It seems for whatever reason, corn rootworm beetles have been emerging a little later than usual this year. It's one generation per year with females laying eggs in cornfields that overwinter and hatch the following year. It's the larvae that cause a lot of damage. They cause lodging potential, which makes harvest difficult and doesn’t allow for maximum photosynthesis."
Different kinds of corn rootworm also have developed resistance to different sites of action — including cry3Bb1 and cry34/35Ab1 Bt traits — and have even undergone diapause to overwinter growing seasons waiting for corn to be planted.
That said, Bauer notes there's a likelihood of higher corn rootworm problems earlier next season — although the environmental conditions in the spring will play a role.
"You can get heavy rains when eggs are hatching, and as long as the soil turns anerobic, you can reduce the number of rootworm larvae in the soil," Bauer says. "But it takes an extended period of time of anerobic conditions to significantly reduce the level of larvae present. If you're starting out and every female is laying 1,000 or 1,800 eggs, you can still have a lot of mortality and have significant pressure in your fields. The best thing is to know what kind of pressure you have and develop a management strategy to protect the roots of your corn crop."
"Growers really need to get out and scout their fields early on to determine the amount of rootworm feeding they have in that July, August, September time frame," Bauer adds. "As growers think about multiple-year strategies, they need to get out in the field to really understand that. The rootworm female can lay 1,000 to 2,000 eggs per season depending on the season and the species themselves. They're very prolific."
Of course, the No. 1 control strategy for reducing corn rootworm pressure is crop rotation. However, it's also important to plant a hybrid with the right traits.
"Many corn hybrids have more than one Bt trait in them," Bauer says. "Make sure to work with your suppliers to plant a hybrid with a pyramided trait stack."
Bauer also recommends using an effective insecticide seed treatment with good, systemic activity to control corn rootworm larvae and complement Bt traits, such as Poncho 1250. He adds Poncho 1250 also includes Votivo, which provides nematode protection for young corn roots.
"Remember at the early stages, corn is very susceptible to those pests," he says.
While cultural practices such as tillage are sometimes recommended to control insect populations in corn residue, keep in mind research continually has shown that tillage doesn't have a significant effect on corn rootworm larval damage.
"The biggest thing is knowing how much pressure you have in the field, and rotation is the best protection you have," Bauer says. "Then you need to start layering everything you have to start managing populations in those fields. Corn rootworms are very difficult to control, and they've developed tolerance to a lot of different practices. We just need to be aware of that and plan our management strategies accordingly."