Almost every year at this time, we see a surge in activity of corn earworm, mostly from large numbers of corn earworm moths that blow up on weather fronts from the southern USA. This year has been unusual so far, in that we are seeing only a slight increase in corn earworm moths, and not yet seeing a large surge. This could change at any point, but it means that for now, growers should be able to get good control of worms in silking corn using insecticide at a less intense schedule than usual for August. At our Ohio sites that reported trap catch this past week, there were 0 to 9 moths in the Scentry type of pheromone trap. The recommended spray interval during hot weather (high >80 F) is every 4 days when traps are catching 3.5 to 7 moths per week, or every 3 days when traps are catching 7 to 91 moths per week, as shown in the table below.
Spray schedule for silking sweet corn.
More information about trap-based spray schedules is available using this link: http://u.osu.edu/pestmanagement/crops/swcorn/ .
We have observed in our Ohio insecticide trials that in years when corn earworm moths are abundant, pyrethroid insecticides such as Warrior, Brigade, Mustang Maxx, Baythroid, and permethrin do not provide very good control even when used at the maximum labelled rate, however in years when corn earworm moths are not very abundant, pyrethroids can provide very good control, if used at the maximum labelled rate.
The other worm pest that is very important during August of most years is the European corn borer. Although this pest has been less abundant during the past 10-15 years than previously, throughout the Midwest, it still can be a key pest of peppers and sweet corn in late summer. We usually see its first generation larvae in June, and its second generation larvae in August. We expect to see larvae once we see the adult moths present, as can be detected by pheromone traps and blacklight traps. The first moths are usually found in traps in the last week of July. However, this year, we are seeing very few moths through mid-August. They are still likely to appear, but they are running a few weeks later than usual.
Trap reports for corn earworm and European corn borer from several Ohio locations can be found using this link: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=0
-Celeste Welty, Extension Entomologist