The most drastic difference in corn insect pressure from 2012 to 2013 was the insects' rate of development. While the exceptionally warm spring of last year accelerated their development, the cool weather this year pushed it back later in the season.
"Last year was a challenge because we had warm weather early and a lot of insects got ahead of our crop and they were waiting for it," says Rich Lee, agronomic service representative for Syngenta in eastern Iowa. "They were sitting at the table waiting for the crop to get dropped on their plate and in a lot of cases that caused problems."
According to Erin Hodgson, Iowa State University Extension entomologist, timing is important. "It depends on when you planted your corn," she points out. "In some situations you had corn rootworm larvae feeding on very small root systems. In a normal year, you have a normal planting date and the roots establish and they can tolerate a little bit more feeding."
Especially in northeast Iowa, more cornfields are showing up with damage from corn rootworm
In 2013, both Lee and Hodgson saw farmers' fields with unexpected damage from corn rootworm, especially in northeast Iowa, along with damage from secondary pests like cutworm. "One thing about insects is they tend to move quickly and some of them, like corn rootworm, you can't go back and fix," says Lee. "You can't always tell what kind of pressure you're going to have. Once you find out, you can't really do much about it in the year that it is occurring."~~~PAGE_BREAK_HERE~~~
Lee says a few days tied up spraying a soybean field in the spring is enough time for cutworms to damage 3,000 to 4,000 plants per acre in a neighboring cornfield. Similarly, a farmer might return from a one- or two-day trip to the state fair during tasseling time only to find rootworm beetles have clipped the silks and caused poor pollination. In preparation for 2014, the threat of such rapid devastation can be reduced with an effective insect management strategy.
"The rootworm pressure is really bad but the good news is we've recognized that. Farmers aren't saying 'I don't know what's going on,' or 'there's nothing I can do,'" says Lee. "They know there's increased rootworm pressure and they know that there are different tools out there, and we're taking advantage of those things."
Rootworm will continue to bug cornfields in 2014, so what can farmers do?
About one-third of Iowa's corn acreage this year is continuous corn. Maybe farmers will have to work more soybeans or other non-corn crops into their crop rotation. "For most of the state I think you would be able to use crop rotation as a fairly effective management strategy, because the corn rootworm larvae will not eat soybean roots or other non-host crop roots," says Hodgson. "You could also consider using a pyramid strategy when choosing a corn hybrid to plant that has the Bt corn rootworm trait. Plant a hybrid that has two or more modes of action against the rootworm larvae."
There is a new Bt corn rootworm trait product that will be available for farmers to plant beginning in 2014, called Duracade. That's good news because it will provide another alternative for farmers to rotate their use of rootworm traits in corn hybrids. "We've got to look at dual-traited rootworm products like the new Agrisure Duracade E-Z Refuge, which will be available on a limited basis in 2014," says Lee. "The rootworm pressure is not backing off; if anything, it just continues to grow, and it requires a bit more management."~~~PAGE_BREAK_HERE~~~
That's not to say rootworm control is as simple as rotate crops or use a corn hybrid that has stacked corn rootworm traits. There are other considerations too, such as location, pest pressure, scouting results and seed selection. "Seed selection is very important. You want to plant the background corn genetics that are a good fit for your farm, depending on some of the pest problems that you have dealt with," says Hodgson.
In addition to rootworm, secondary corn insect pests are another problem to consider
Secondary pests like to keep farmers guessing too, and not all of them are controlled by Bt traits in corn hybrids. "There are other insects besides rootworm out there and a soil-applied insecticide like Force will help pick up and control some of those pests," says Lee. Without a crystal ball, no one can guarantee which secondary pest will show up, or when, but farmers can certainly expect to see some type of insect pressure in the year ahead. "You just can't always trust these bugs," says Lee. "They're sitting out there and if the opportunity presents itself, they can really go to town. But they are always out there, they're never gone. Whose turn is it going to be next year? That's the thing you just can't predict."
Farmers don't have to guess blindly though. Historical pressure and proper scouting can help them prepare appropriately. "If you are scouting on a regular basis and you have done it for many years you can make an educated guess on what kind of pests may show up next year," says Hodgson. "It depends on where you are within the state; it's just kind of year-to-year which insects flare up."
"Every year, we get just a little smarter and things are always changing, but we've got so many more tools for insect control than we've had in the past, I think," says Lee. "These tiny insects have caused farmers big problems in the past, but as we try to help farmers grow more corn, we're starting to realize that together, maybe we just need to work a bit harder on controlling these bugs."