The extremely cold temperatures Iowa experienced this past winter reduced the overwintering population of some insect pests but had little impact on others. You still need to keep an eye on fields, scouting and managing yield-robbing pests.
For corn, black cutworm is the first pest to watch for as soon as the crop begins to emerge in the spring. This insect doesn't overwinter in Iowa, explains Iowa State University Extension entomologist Erin Hodgson. Instead, adult moths migrate on the wind, flying up from southern states in early spring. Upon arrival the moths mate and lay eggs. Eggs are laid in crop stubble, low spots in fields and in weedy areas. The eggs hatch and young larvae, the worm stage, injure corn plants by feeding on leaf tissue. The older, larger larvae can cut off young corn plants and reduce stands. Once corn reaches the V5 growth stage, it becomes harder for the pest to cut plants.
Start watching for black cutworm when corn emerges
Black cutworms can be confused with another insect that may be found in fields, the dingy cutworm. Dingy cutworm may feed on leaves of young corn seedlings, but dingys don't clip off plants. There are characteristics that can help you tell the difference between blacks and dingys, such as skin type and tubercle size, outlined in detail in an ISU Integrated Crop Management article Blacks and Dingys: Confusing Cutworms.
ISU field agronomists and agribusiness partners participate in the North Central ipmPIPE black cutworm monitoring effort. This network helps growers determine when to start scouting. Scouting fields is important in determining if cutting larvae are a problem in a specific field. "While the adult moth traps scattered across the state capture some moths to give us an idea of when they arrive in an area, that alone isn't enough to justify applying an insecticide treatment," says Hodgson. "You need to scout fields to see if black cutworms are present. If an infestation reaches the economic threshold, insecticide application can be justified."
Based on dates when moths arrive, scouting dates are predicted. When scouting dates have been estimated, they're posted in ISU's Integrated Crop Management newsletter. As with other insects the cutworm threat depends on accumulation of growing degree days and weather factors.
Another pest to watch out for is bean leaf beetle
Another pest to watch for is bean leaf beetle on soybeans. As a result of this past winter's bitter cold, predicted mortality of bean leaf beetle is high, she says. Most bean leaf beetle adults won't survive when air temperatures fall below 14 degrees, although they have adapted to winter by seeking cover under crop residue and in loose soil.
Central and northern Iowa experienced the coldest temperatures, so most bean leaf beetle adults aren't expected to survive. Beetle mortality in southern Iowa, however, wasn't quite as high. Although overwintering beetle populations are expected to be low this year, soybean growers are still advised to keep an eye out for this insect this spring, Hodgson advises.
It's important to scout soybean fields when the first plants emerge in the area. Pay particular attention to soybeans planted near alfalfa fields and fields with a history of bean leaf beetle problems. Overwintering adults seeking a food source will quickly move into fields with emerging soybeans and chew the leaves of young plants. For more information read the ICM news article.
What about corn rootworm this year?
The bitter cold also likely contributed to an increase in mortality of corn rootworm eggs overwintering in the soil. This is especially likely in areas that had little to no snow during those periods of extreme cold. However, no matter where you farm in Iowa, Hodgson recommends that you check corn roots for signs of rootworm damage later on in the 2014 growing season—to help you manage for rootworm in those fields next year.
The 2013 ISU research trial summary on corn rootworm and other soil insects is posted on the ISU Corn Rootworm website. The report is on the far right side of the page along with other reports going back to 2005.