Monday, July 29, 2019

European Corn Borer - Scouting & Monitoring

Adult European Corn Borers; Credit: University of Missouri
Since its introduction to the United States, the European Corn Borer (Ostrinia nubilalis) has gradually become a damaging pest to corn and other commercially valuable crops. They range from having 1-4 generations per year, which is heavily influenced by in-season weather and native predators/parasites. As the borers hatch out they feed on whorls and emerging tassels until those tassels open up. Once this occurs they proceed downward and, like their name suggests, bore into stalks eventually making their way to the ears through the side, base or tip.

There are two strains identified: New York (Z) and Iowa Strain (E). Each are present at varying levels in different areas, but it is not uncommon to have one or the other. Since corn borer larvae reside in stalks and other plant matter, they are highly adapted to overwinter in cold climates. Due to their preference for monocultured areas common in commercial cultivation, these borers present growers with a number of difficult tasks to achieve control. We will cover the first step growers should take here – trapping & monitoring.

European Corn Borer Larva; Credit: University of Missouri
Trapping needs to be done early in the season beginning prior to the first flight of adult moths. First flight will occur once temperatures warm in spring, but varies quite a bit from location to location. Thankfully, many agricultural extensions keep tabs on corn borer distribution, emergence time and population estimates where they have been identified. These extensions also track the strain(s) of corn borers present in your locale as well as generalized ratios that they are present in. For these reasons, it is highly recommended to consult with your local extension before the growing season starts.

Once you have done so, placement of pheromone baited traps is important to stay ahead of the borer population. If it is confirmed that both the New York and Iowa strains are present, two separate traps should be used. Bait one with a lure for the New York strain and the other with a lure for the Iowa strain. Place these traps at least 50 feet apart on the borders of corn fields or edges of the growing area. Traps should be placed so that the trap bottoms remain around the height of any weeds or other plants in the border area. Population estimates can be made based on the quantities captured, but scouting does not end then.

Scentry Wing Trap
Once trapped adults are spotted, scouting should be done weekly by tassel inspection of 50-100 plants in groups of 10. Keep a sharp eye out for any larvae, new feeding damage or frass. If corn is in the whorl stage, simply pull the developing tassel out and inspect it for larvae and frass. If tassels have already emerged, scouting can be done without removing the tassel. These weekly scouting ventures allow you to make timely decisions on pesticide usage to maximize their effectiveness and minimize costs in both controls and yield losses. Generally, if greater than 15% of plants in the area have larvae present a spray should be applied.

For additional information and control options for European Corn Borer control, visit our website at

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