While walking through a sweet corn plot this morning looking at how many plants were tasseling, I saw a few interesting things to quickly comment on in case growers are seeing these things in their fields.
I saw some rough chewing damage on the leaf and immediately thought, wow, it looks like we have some Fall armyworm in this plot (despite having a FAW pheromone trap nearby that has caught zero moths for weeks). Upon closer inspection, it was a grasshopper inside the rolled up leaf. As I looked at the grasshopper, I noticed the frass around the leaf damage was not wet and messy typical of the pest but rather thinner, pelletized and fairly cylindrical. So even if the grasshopper had left the leaf, the “frass” would be a good clue it wasn’t a caterpillar.
As I began inspecting the tassels, I saw a lot of corn leaf aphid on just about each tassel. This sucking pest can be a problem if it exudes too much honey dew (sugary liquid waste excretion) on the tassel and it interferes with pollen shed and possibly pollination. While you can spray insecticides to knock down the aphids, be sure to take a look for natural enemies such as ladybug adults and larvae, green lacewing larvae, and hover fly larvae.
One of the biggest pests of sweet corn has been a little quiet for the past few months according to our trapping network, but we expect it to pick up in the next few weeks so be sure to have your corn earworm trap out near fresh silking corn with a fresh lure. See the nice summary below by Celeste Welty a few weeks ago with reference to spray frequency of CEW.
The corn earworm moths will be laying their eggs on (fresh) silks of sweet corn. Sweet corn can be protected from corn earworm infestation by insecticide sprays during silking. When the number of CEW moths caught in traps is moderate (1 to 13 moths per day, or 7 to 90 moths per week), then sprays should be applied every 4 days if the daily maximum temperatures is below 80 degrees F, or every 3 days if the daily maximum temperatures is above 80 degrees F. More information about CEW, traps, and trap-based spray schedules is available using this link: http://u.osu.edu/pestmanagement/crops/swcorn/ .