Corn earworm arrived early in sweet corn

Corn earworm has showed up unusually early this year and has been infesting early sweet corn that was not adequately protected. The earworm population as detected by moths caught in pheromone traps was very high in early June (161 moths in one trap in one week in Columbus), and again in late June at some sites (125 moths in one trap in one week). However, this past week, the number of moths caught dropped greatly (7 in one trap at Columbus). Similar trends have been reported from other parts of Ohio. As long as corn earworm moths are active, sweet corn fields that are in the early silk stage will become infested by corn earworm unless preventive measures are taken. The infestation will be less intense in sweet corn fields if the local fields of grain corn are in the silking stage, but due to the early summer rains causing delay in planting, grain corn in much of Ohio is not yet at the silking stage, thus sweet corn will be extra vulnerable to earworm attack. Once corn earworm is detected, silking sweet corn should be sprayed with insecticide every 2-6 days. The choice of an appropriate spray interval is as important as the choice of product to use. Details about the most appropriate spray interval based on pheromone traps are shown in the chart below.

Growers who do not yet have a trap can find information about buying a trap with this link: https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/07/TrapSpecsAndSources2019.pdf

and information about using the trap with this link:

https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2014/12/CornTrapInstructions2009-u47rp3.pdf

Our testing of insecticides for corn earworm control over the past 13 years has shown that pyrethroids (Warrior, Asana, Pounce, Mustang Maxx, Brigade, Baythroid, Hero) are generally effective for earworm control when the earworm population is low to moderate but generally not effective when the population is high. If pyrethroids are used, they should be used at the maximum labeled rate. Among pyrethroids, Hero is generally the most effective; it is a pre-mix of two different pyrethroids (Mustang Maxx and Brigade). Alternatives to pyrethroids are Coragen, Radiant, and Blackhawk, and the pre-mix Besiege, which was formerly called Voliam Xpress. Organic growers can use Entrust or a B.t. such as Javelin or Dipel.

For plantings of B.t. transgenic hybrids (the Attribute II series and the Seminis Performance series), we have found that the B.t. provides adequate control of corn earworm when populations are low, but not when earworm populations reach high density. These hybrids provide the best control when silks are fresh but less control when silks begin to dry. Thus insecticide sprays during the later part of the silking period are helpful to prevent earworm infestation in transgenic sweet corn.

-Celeste Welty & Jim Jasinski

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