Sweet Corn IPM Newsletter No. 11 — September 8, 2023


Corn Earworm Larvae
Corn Earworm Larvae; photo by David Handley

Earworm and Fall Armyworm Threaten Remaining Corn

This will be the final issue of the Sweet Corn IPM Newsletter for the 2023 season. I would like to thank all the growers who participated in the program this year, and our team of IPM scouts, including Chantal Cyr, Ethan Handley and Sean McAuley. Thanks also to Stephanie Wright and Chris Howard for editing and mailing the newsletter, and updating our webpage and blog.


Despite warm temperatures and clear nights, pest activity has remained relatively moderate for this point in the season. Corn earworm remains the biggest threat to silking corn, although fall armyworm has been over threshold in a few fields. Continued warm weather will likely keep the moths active through the remainder of the season.

European corn borer: A second generation of moths appears to be underway in a couple of southern locations, but most fields are no longer seeing this insect as a threat. Moth counts were over the 5-moth/week threshold for silking corn only at one site in Dayton this week. As the season comes to an end, remember that plowing down corn stalks and stubble will destroy the overwintering sites of European corn borer, and can help reduce infestations next season.

Corn earworm: Moth counts were moderate for this late in the season, but still pose a threat to any fresh silking corn remaining in fields this week. Based on this week’s moth counts, a 4-day spray interval for silking corn was recommended for Biddeford, Bowdoinham, Cape Elizabeth, Corinth, Dayton, Monmouth, Wayne and one Wells site. A 5-day spray schedule was recommended for Auburn. A 6-day spray interval was recommended for New Gloucester and one Wells site. Under very high temperatures, moth activity may be higher, so growers should shorten spray intervals by one day if temperatures are over 80F for more than two days.

Fall Army Worm on Pre-tassel Corn Plant
Fall Army Worm on Pre-tassel Corn; photo by David Handley

Fall armyworm: Moth counts were a little higher at several locations, but remain lower than expected for this late in the season. Bowdoinham, Dayton, Monmouth and New Gloucester were over the three-moth threshold for silking corn. Sprays for corn earworm at these sites should also provide control of fall armyworm.

Maine Vegetable & Small Fruit Growers Twilight Meeting
Wednesday, Sept. 13, 5:30 pm, Chick’s Apple & Berry Farm, 571 Main Street, Monmouth, ME.
Join host Paul Peters for a tour of this PYO farm featuring apples, raspberries, blueberries and strawberries, and a discussion of pest issues, including invasive weeds. One pesticide applicator re-certification credit will be available.

University of Maine Highmoor Farm Open House
Thursday, Oct. 5, 5 pm, 52 Rt. 202, Monmouth ME.
Come and view the vegetable variety trials at Highmoor Farm, including artichokes, celery, eggplant, and pumpkins of all shapes, colors and sizes.


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259

UMaine Extension Diagnostic Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473

Sweet Corn IPM Weekly Scouting Summary

Location CEW Moths ECB Moths FAW Moths %Feeding Damage Recommendations / Comments
Auburn 6 0 0 5-day interval recommended for silking corn
Biddeford 10 0 1 4-day interval recommended for silking corn
Bowdoinham 8 1 3 4-day interval recommended for silking corn
Cape Elizabeth 10 0 0 4-day interval recommended for silking corn
Corinth 15 1 1 4-day interval recommended for silking corn
Dayton I 24 0 8 4-day interval recommended for silking corn
Dayton II 42 24 9 4-day interval recommended for silking corn
Lewiston 2 0 0 6-day interval recommended for silking corn
Monmouth 34 0 9 4-day interval recommended for silking corn
New Gloucester 2 0 10 6-day interval recommended for silking corn
Oxford 0 0 0 No spray recommended
Wayne 10 0 0 4-day interval recommended for silking corn
Wells I 2 0 0 6-day interval recommended for silking corn
Wells II 9 3 0 4-day interval recommended for silking corn

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm

Corn Earworm Spray Thresholds for Pheromone Traps

Moths caught per week Moths caught per night Spray Interval
0.0 to 1.4 0.0 to 0.2 No spray
1.5 to 3.5 0.3 to 0.5 Spray every 6 days
3.6 to 7.0 0.6 to 1.0 Spray every 5 days
7.1 to 91 1.1 to 13.0 Spray every 4 days
More than 91 More than 13 Spray every 3 days

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer Thresholds

Whorl stage: 30% or more of plants scouted show injury.
Pre-tassel-silk: 15% or more of plants scouted show injury.
Silk: 5 or more moths caught in pheromone traps in one week.

IPM Web Pages:

Explore Integrated Pest Management in Maine — UMaine

Integrated Pest Management Data Visualization Tool — Penn State

Integrated Pest Management — UMass Amherst

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

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