Very large numbers of corn earworm moths have been detected in pheromone traps for the past few days.
Reports from South Charleston in southwestern Ohio are for 185 moths on 8/10 for just one night, after 560 moths total in the previous 3 nights. In Columbus, we had 343 moths in 2 nights, 8/9 and 8/10, after 106 moths the previous 2 nights. These moth numbers mean that sweet corn fields that are in the early silk stage will become heavily infested by corn earworm unless preventive measures are taken as soon as possible.
Now that most of Ohio’s grain corn is starting to dry out, any patches of sweet corn are likely to be attacked by this pest. 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:
Our testing of insecticides for corn earworm control over the past 12 years has shown that pyrethroids (Warrior, Asana, Pounce, Mustang Maxx, Brigade, Baythroid, Hero) are generally effective for earworm control in years when the population is low to moderate but generally not effective in years 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, Brigade). Alternatives to pyrethroids are Coragen, Radiant, and Blackhawk. 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 only fair control 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 sprays during the later part of the silking period are helpful to prevent earworm infestation in the transgenic hybrids.
-Celeste Welty & Jim Jasinski