"We first noticed it probably about 5 years ago," said Mike Tiedeman, an agronomist with Farmers Coop Society in Ireton, Iowa.
Tiedeman is talking about corn rootworm that is becoming resistant to the corn specifically designed to kill it.
Rootworm is why farmers have been planting what's called "BT" corn for more than a decade.
"The worm takes a bite of the root, and in theory, is supposed to die," said Tiedeman.
But that's happening less now.
Some species of rootworm in Siouxland are becoming resistant to "BT" corn. The stuff just isn't killing them as well anymore.
Tiedeman says this could be because some farmers grow corn year after year.
A continuous corn crop helps rootworm thrive.
It could also be due to a historical lack of refuge acres.
Farmers are supposed to be planting corn that the rootworms can eat, along with "BT" varieties, in an effort to stop resistance to the GMO.
But Tiedeman says some farmers have been lax about taking that step.
"I think there were a lot of scenarios where guys were assuming 'my neighbor's planting the refuge'," said Tiedeman.
While "BT" resistant rootworm has popped up in Northwest Iowa, farmers can do a few things to stop the pests.
Tiedeman says farmers should start by planting different varieties of "BT" corn to try and find something the rootworms aren't resistant to.
Farmers could also add insecticides when caring for their crop.
Tiedeman also suggests that, if possible, farmers who plan corn continuously in the same field should try a crop rotation schedule, putting soybeans in fields that have been continuous corn for years.
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