Sweet Corn IPM Newsletter No. 7 — August 15, 2025
FALL ARMYWORM PRESSURE INCREASING
Corn Earworm Counts Remain Low-Moderate
Situation
It’s official: most of southern and coastal Maine is now under drought conditions, according to the National Weather Service. In addition, there does not appear to be any relief in sight in the near term. Growers are struggling to keep crops irrigated and maintain their water supplies. Many corn fields are under drought stress, which can lead to poor tip fill, reduced ear size, and significant crop loss. Corn earworm and fall armyworm numbers remain low, as there have been no weather fronts from the south to move them into Maine.
European corn borer: Moth counts were very low again this week, with the exception of our most western site in Oxford, which was over the 5 moth threshold for silking corn. This may be the start of a second generation of this pest, but it will likely vary from site to site.
Corn earworm: Moth numbers were low again at most locations this week, as the dry weather appears to be slowing the movement of moths into the state. Only four sites are now on a recommended spray schedule for fresh silking corn. A five-day spray interval for silking corn was recommended for Gray; a six-day spray interval was recommended for Dayton, Wayne, and one Wells location.
Fall armyworm: Moths counts in pheromone traps exceeded the control threshold (3) for silking corn in Biddeford, Cape Elizabeth, Durham, Garland, Gray, Lewiston, and Monmouth this week. Only the Gray site is not presently under a spray interval for earworm, so sprays to protect silking corn were recommended at all others. Armyworm feeding damage on pre-tassel corn was higher at some locations this week. Sprays were recommended at Biddeford, Bowdoinham, and Cape Elizabeth where damage exceeded the control threshold of 15%.
Western Bean Cutworm: Depending on location, moth counts ranged from 0 to 30 in our pheromone traps this week, suggesting that the peak in the flight of this pest may be ending. Fields presently under a spray interval for corn earworm or fall armyworm should not require additional coverage. A spray for western bean cutworm on silking corn was recommended for Bowdoinham, Farmington and one Wells site.
Corn leaf aphids: We want to re-emphasize that aphid infestations on corn have been observed in most fields over the past two weeks. Colonies of these bluish-green insects can cover the tassels, stalks and husks. The waste aphids excrete on the plants stimulates the development of sooty mold, which coats the surface of the husks, and reduces the marketability of the ears. Insecticides that target aphids include Assail®, Asana®, Warrior® and Lannate®.
Squash vine borer: No sites exceeded the five moth per week threshold this week.
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 | 0 | 0 | 19 | 22% | One spray for FAW on silking corn and pre-tassel corn |
| Bowdoinham | 0 | 0 | 1 | 15% | One spray for western bean cutworm (see text above) |
| Cape Elizabeth | 0 | 0 | 43 | 31% | One spray for FAW on silking corn and pre-tassel corn |
| Dayton | 3 | 0 | 0 | 0% | 6-day spray interval recommended for silking corn |
| Durham | 1 | 0 | 7 | One spray for FAW on silking corn | |
| Farmington | 1 | 0 | 1 | One spray for western bean cutworm (see text above) | |
| Garland | 0 | 6 | 3 | One spray for ECB and FAW on silking corn | |
| Gray | 7 | 0 | 21 | 5-day spray interval recommended for silking corn | |
| Lewiston | 0 | 0 | 4 | One spray for FAW on silking corn | |
| Monmouth | 0 | 0 | 4 | One spray for FAW on silking corn | |
| Oxford | 1 | 9 | 5% | One spray for ECB on silking corn | |
| Palmyra | 0 | 0 | 0 | No spray recommended | |
| Wayne | 2 | 1 | 1 | 0% | 6-day spray interval recommended for silking corn |
| Wells I | 2 | 0 | 0 | 6-day spray interval recommended for silking corn | |
| Wells II | 1 | 0 | 2 | 1% | One spray for western bean cutworm (see text above) |
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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