Sweet Corn IPM Newsletter No. 5 — August 1, 2025
PEST PRESSURE MODERATE THIS WEEK
Most Silking Corn Remains On A Protective Spray Schedule
SITUATION
Early sweet corn harvest is under way in much of southern and central Maine this week. Quality continues to be reported as very good. Dry conditions continue to dominate, so growers are irrigating wherever possible. Pest pressure was moderate this week, as the weather has not been favorable for migrations of moths into the state.
European corn borer: Moth counts remain very low this week. Trap captures of moths exceeded the control threshold (5) for silking corn in Palmyra and Garland. Larvae are still feeding in fields, and scouting for damage should continue. However, none of the fields scouted this week were over the damage threshold of 15%.
Corn earworm: Moth numbers were lower at most locations this week, although nearly all sites require protection of fresh silking corn to prevent infestation. A four-day spray interval for silking corn was recommended for Dayton and Gray; a five-day interval was recommended for Cape Elizabeth, Durham and one Wells site; a six-day spray interval was recommended for Biddeford, Bowdoinham, Garland, Lewiston, Monmouth and Oxford. Fields not yet in silk do not need to be protected from corn earworm.
Fall armyworm: Moths counts in pheromone traps exceeded the control threshold (3) for silking corn in Biddeford, Cape Elizabeth, Gray, Lewiston, Monmouth, Oxford, Wayne and one Wells site this week. Single sprays for silking corn were recommended for the Wayne and Wells sites, which are not presently under a spray interval for earworm. Armyworm feeding damage was low this week. None of the sites scouted exceeded the control threshold of 15% injury.
Western Bean Cutworm: Depending on location, moth counts ranged from 1 to 80 in our pheromone traps this week, indicating a peak in the flight of this pest. Nearly all sites were over our suggested threshold of three moths per week, but most fields are presently under a spray interval for corn earworm or fall armyworm. A spray for silking corn was recommended at the Farmington site.
Corn leaf aphids have been observed in several fields. Aphids often infest corn fields that have not recently been sprayed for other pests. These small, bluish-green insects can cover the tassels, stalks and husks. The waste produced by the aphids, called “honeydew” stimulates the development of sooty mold, a slimy fungus that coats the surface of the husks, reducing the marketability of the ears. Sprays applied for corn earworm usually control aphids. Sprays specifically for aphids would only be recommended if sooty mold is becoming a problem.
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- Aphids on Corn Tassel; photo by Kaytlin Woodman
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- Aphids on Corn; photo by Kaytlin Woodman
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- Aphids on Corn; Photo by D. Handley
Squash vine borer: No sites were over the five moth per week threshold, indicating that the first generation of squash vine borer may be at an end for this season.
Cucurbit Downy Mildew Alert: This important disease of cucumbers, melons and squash has been confirmed in Massachusetts and New Hampshire. For more information, you may view the alert with additional resources and photos visit the Highmoor homepage.
Sincerely,
David T. Handley
UMaine Extension Vegetable & Small Fruit Specialist
Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259
207.933.2100
UMaine Extension Diagnostic Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279
| Location | CEW Moths | ECB Moths | FAW Moths | %Feeding Damage | Recommendations / Comments |
|---|---|---|---|---|---|
| Biddeford | 3 | 0 | 49 | 0% | 6-day spray interval recommended for silking corn |
| Bowdoinham | 3 | 0 | 0 | 6-day spray interval recommended for silking corn | |
| Cape Elizabeth | 5 | 0 | 17 | 2% | 5-day spray interval recommended for silking corn |
| Dayton | 10 | 0 | 0 | 0% | 4-day spray interval recommended for silking corn |
| Durham | 4 | 0 | 1 | 2% | 5-day spray interval recommended for silking corn |
| Farmington | 0 | 0 | 0 | 0% | One spray for western bean cutworm (see text above) |
| Garland | 2 | 5 | 2 | 0% | 6-day spray interval recommended for silking corn |
| Gray | 9 | 0 | 42 | 0% | 4-day spray interval recommended for silking corn |
| Lewiston | 3 | 0 | 3 | 0% | 6-day spray interval recommended for silking corn |
| Monmouth | 3 | 0 | 7 | 6-day spray interval recommended for silking corn | |
| Oxford | 2 | 1 | 3 | 5% | 6-day spray interval recommended for silking corn |
| Palmyra | 0 | 5 | 0 | 0% | One spray for ECB on silking corn |
| Wayne | 0 | 0 | 3 | 0% | One spray for FAW on silking corn |
| Wells I | 6 | 0 | 1 | 2% | 5-day spray interval recommended for silking corn |
| Wells II | 1 | 0 | 3 | 2% | One spray for FAW on silking corn |
CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm
| 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 — UMass Amherst
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