Rotation And Refuge Key Ways To Stave Off Rootworms

Rootworms that chew through GMO corn typically come from continuous corn fields.

Published on: Feb 20, 2012

A farmer stood on the back of a tour wagon at a seed corn company recently as the group toured plots, and bragged about how he got around the refuge rules. He claimed he had never planted refuge acres, never intended to, and that he didn't know of any neighbors who did either.

He lived in Indiana, so by all accounts, his fields haven't been attacked by rootworm larvae that can survive on roots bearing the Cry3Bb1 event toxin. So far the outbreaks have been in western states- Iowa, Minnesota, parts of Illinois, perhaps parts of Wisconsin. Needless to say, I won't know if his fields are ever infested with those variants, because after hearing him boast about thumbing his nose at resistance, he wasn't someone I wanted to get information from as a possible future source for a magazine or Web article.

Let's hope he lives in a pocket where farmers don't understand the need for refuge, and it's not widespread. Theories from so-called experts claim that while most farmers allow for refuge, compliance is not as high as it should be.

Ken Ostlie from the University of Minnesota suggests that failure to leave as much refuge as necessary may be one of the factors leading to breakthroughs in rootworm feeding on GMO corn for that one, single event in his part of the world. He has documented the case in many fields, and has even conducted research, trying to pinpoint exactly why the rootworm larvae are able to break through the control mechanisms.

Refuge helps in theory because if a mutation survives in the GMO acres that can attack roots even with the GMO toxin, it will likely mate with a susceptible rootworm if there are refuge acres nearby, since they will be the biggest share of the surviving population, and the offspring will also be susceptible to the event.

The other factor driving resistance is constant exposure to corn, and constant exposure to the same control mechanism year after year, Ostlie notes. The best advice in areas where it has already occurred is to rotate to soybeans if possible, use an event that is still effective e against rootworm larvae, and whichever way you choose, whenever you are planting GMO corn, follow the refuge requirements.

Companies are moving toward refuge-in-a-bag systems, but not all companies are totally there yet. Be sure you understand the refuge requirements of the hybrids that you will plant, and if necessary, ask a  seedsman for help in interpreting how much refuge you need, what type of refuge, and what options you have for laying it out in the field.