Sweet Corn IPM Newsletter No. 9 — August 25, 2023


Fresh Silking Corn Remaining Requires Protection

Corn in Silk Stage
Corn in Silk Stage, photo by David Handley


Last week’s storms appear to have brought up a wave of corn earworm moths, as numbers climbed in most locations this week. Other pest numbers have been lower in most fields, with the exception of four-legged species. Deer, raccoons, skunks and coyotes have been problematic at many sites.

European corn borer: Most fields are in silk or beyond at this point, so we have not been field scouting, unless a field is not under a spray schedule for corn earworm. Counts were over the 5-moth/week threshold for silking corn in Biddeford, Bowdoinham, Dayton, Oxford and one Wells site, where a partial second generation appears to be underway.

Corn earworm: Moth counts were again higher in nearly all locations this week. Based on this week’s moth counts, a 3-day spray interval for silking corn was recommended for Cape Elizabeth, A 4-day spray schedule was recommended for Auburn, Biddeford, Bowdoinham, Dayton, Garland, Lewiston, Monmouth, New Gloucester, Oxford and Wells. A 6-day spray interval was recommended for Palmyra.

Fall armyworm: Moth counts were low at most sites this week. Biddeford, Garland, Monmouth, and New Gloucester were over the three-moth threshold for silking corn.

Western Bean Cutworm: Moth numbers were generally low this week, suggesting that this pest may no longer be a threat in most locations for the remainder of the season. Populations of this pest tend to drop off very rapidly toward the end of August.

Cucurbit downy mildew alert: With ongoing moist weather there continues to be a high risk for cucurbit downy mildew. The strains presently being found in Maine primarily infect cucumber, cantaloupe, and cabbage family crops. Producers of these crops should apply protectant fungicides prior to any future storms. These are listed in the New England Vegetable Management Guide. Chlorothalonil or copper products are protectant fungicides that most growers probably already have on-hand. It may be worth switching to fungicides with specific activity against CDM. They can also be found in the New England Vegetable Management Guide. There have not yet been reports of the strain of downy mildew that affects pumpkins and winter squash in Maine. However, it is important to monitor your crops regularly, and keep an eye out for symptoms of CDM. Excellent photos and more information about this disease can be found here: Cornell Vegetables — Cucurbit Downy Mildew.


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 32 0 0 4-day interval recommended for silking corn
Biddeford 54 13 8 4-day interval recommended for silking corn
Bowdoinham 28 8 1 4-day interval recommended for silking corn
Cape Elizabeth 100 3 0 3-day interval recommended for silking corn
Dayton 86 42 1 4-day interval recommended for silking corn
Farmington 0 0 1 No spray recommended
Garland 51 0 7 1% 4-day interval recommended for silking corn
Hollis 0 0 0 No spray recommended
Lewiston 32 0 1 4-day interval recommended for silking corn
Monmouth 49 4 10 4-day interval recommended for silking corn
New Gloucester 58 0 13 4-day interval recommended for silking corn
Oxford 25 6 2 4-day interval recommended for silking corn
Palmyra 2 0 0 6-day interval recommended for silking corn
Wayne 1 4 0 No spray recommended
Wells I 42 0 0 4-day interval recommended for silking corn
Wells II 62 8 1 7% 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.

In complying with the letter and spirit of applicable laws and pursuing its own goals of diversity, the University of Maine System does not discriminate on the grounds of race, color, religion, sex, sexual orientation, transgender status, gender, gender identity or expression, ethnicity, national origin, citizenship status, familial status, ancestry, age, disability physical or mental, genetic information, or veterans or military status in employment, education, and all other programs and activities. The University provides reasonable accommodations to qualified individuals with disabilities upon request. The following person has been designated to handle inquiries regarding non-discrimination policies: Director of Equal Opportunity, 5713 Chadbourne Hall, Room 412, University of Maine, Orono, ME 04469-5713, 207.581.1226, TTY 711 (Maine Relay System).