New York State IPM Program

Did You Notice More Worms in Your Sweet Corn This Fall?

Marion Zuefle, Vegetable IPM Extension Area Educator, authors today’s post. She works out of the NYSIPM Program office at Cornell AgriTech in  Geneva, NY.

Corn earworm, one of the major insect pests of sweet corn, had a banner year in 2018.

Every year sweet corn growers battle diseases, weeds, and insects that can make their crop unmarketable if they’re not controlled. This year is no exception. Considering everything a grower might face, producing a perfect ear of corn can be difficult. Fluctuations in weather, such as extreme droughts one year and excessive rain the next, directly impact corn and corn pest populations. In addition to increased pest pressure, growers also have to consider development of pest resistance to insecticides.

Such was the case for this year’s top sweet corn pest, the corn earworm (CEW for short). Here at NYS IPM we have monitored CEW flights along with three other common sweet corn pests (European corn borer, fall armyworm, and western bean cutworm) since 1994. Every year traps are placed at locations throughout NY to determine when the adult moths of these pests begin to fly. A rise in captures prompt growers to begin scouting their crops to see if pest levels are high enough to warrant control.  This monitoring and trap network is a critical component of practicing good IPM.

Corn earworm

This year we saw one of the highest flights of CEW since we began monitoring back in 1994. Only 2007 and 2010 have been higher. And this year boasted the single highest trap catch ever recorded for one site since we began: 341 CEW moths caught in a single week at one location om

CEW’s wide host range includes many other vegetable crops, field crops, fruit, ornamentals, and weeds. Its preferred host, of course, is corn. Adults lay single eggs on the silks of the corn ear. When the larvae emerge, they feed on the silks and then enter the ear to feed on kernels. Because eggs are deposited singly and are the size of a pinhead, it is very difficult to scout for corn earworm. Once hatched from these tiny eggs, larvae immediately enter the ear leaving almost no visible external damage until the husk is pulled back.

Corn earworm egg on silk

CEW are difficult to control with insecticides, because it takes precise timing to target larvae before they enter the corn ear and become protected from sprays. For this reason, growers rely heavily on trap catch data informing them when flight starts and how heavy the pest pressure is in a given year.

This year’s significant CEW flight likely resulted from several factors. They include weather patterns and storm fronts that bring moths north from their overwintering sites. There has also been an increase in the overwintering potential of this pest in NY. We have at least two known locations—one in Erie county and on in Onondaga county—that have earlier than usual CEW catches, an indication of successful overwintering populations. In addition to increased population pressure, CEW has developed resistance to some insecticides (pyrethroids) as well as field-evolved resistance to some types of Bt corn (corn that expresses Bacillus thuringiensis (Bt) proteins with insecticidal properties).

Marion Zuefle checks a trap used in the Sweet Corn Pheromone Trap Network.

What can you do?

As a consumer, reconsider your expectations for perfect produce. For the most part, CEW damage is limited to the tip of the ear. Rather than refuse to purchase anything resembling pest damage, simply cut off the tip of the cob.

As a grower, now is the time to sign up to follow our SWEET CORN Pheromone Trap Network Blog  where pest information and trap counts are posted weekly during the season. You’ll receive emails when a new post appears.

Learn more about vegetable production at our NYSIPM Program Vegetable Page

 

Author: Debra E. Marvin

Community IPM Program Assistant for Schools, Daycare and Horticulture. New York State Integrated Pest Management Program, Cornell University, New York State Agricultural Experiment Station, 630 W. North Street, Geneva, NY 14456 Email: dem35@cornell.edu

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