Courtesy University of MinnesotaEven a few corn earworm moths can cause considerable damage if your sweet corn field is the only one around that's silking.For several decades, Midwestern sweet corn growers have followed the recommendation to only treat their corn if they pick up 10 or more corn earworm moths per night in a pheromone trap and if the corn is in the vulnerable green silk stage.
But Rick Weinzierl, Extension entomologist with the University of Illinois, is causing some of his fellow researchers to reconsider that treatment threshold, according to a grower newsletter.
During much of the growing season, female corn earworm moths have thousands up thousands of acres of corn—field and sweet—on which to lay their eggs.
But early spring sweet corn is a different story.
It starts silking long before neighboring field corn.
As a result, moths are attracted to the early sweet corn like a magnet.
If your sweet corn is silking earlier than any of the neighboring field corn, Purdue University entomologist Rick Foster recommends treating if you catch any corn earworm moths in pheromone traps.
And he recommends treating as long as green silk is present, with two to five days between sprays, depending on temperatures and moth catches.
Once neighboring fields start to silk, then go back to the 10 moths per night threshold.
Foster also recommends similar treatment of very late sweet corn that silks when neighboring field corn has dried down.
He and colleagues will be conducting trials this summer to test the new threshold.