Sweet Corn IPM Newsletter No. 6 — August 8, 2025
CORN EARWORM PRESSURE MODERATE
Silking Corn Threatened By Fall Armyworm, Western Bean Cutworm
SITUATION
Very warm, dry weather continues to speed corn growth. Some fields intended for Labor Day harvest will likely be ready much earlier. Quality continues to be very good, especially in fields that have been irrigated through the dry spell. Pest pressure continues to be moderate this week, with corn earworm and fall armyworm numbers lower. Only western bean cutworm has widespread numbers of concern this week.
European corn borer: Moth counts remain very low this week. Trap captures of moths exceeded the control threshold (5) for silking corn only in Palmyra. Very little larvae feeding has been found in fields. While it appears the first generation of borer is over, a second generation of this pest, usually very late in the season is possible.
Corn earworm: Moth numbers remain low at most locations this week, with only four sites on a recommended spray schedule for fresh silking corn. A four-day spray interval for silking corn was recommended for Gray and one Wells site; a six-day spray interval was recommended for Bowdoinham and the other Wells location. 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, Monmouth, Oxford, Wayne and one Wells site this week. Sprays for silking corn were recommended for Biddeford, Monmouth, and the 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 3 to 122 in our pheromone traps this week, indicating a continued peak in the flight of this pest. All sites were over our suggested threshold of three moths per week, but 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 Dayton, Durham, Farmington, Lewiston and Oxford.
Corn flea beetles have been observed in several fields over the past few weeks. In high numbers these insects can injure young, whorl stage corn, but are more often a concern because they can spread bacterial wilt, also known as Stewart’s wilt, a serious disease of corn. Most sweet corn varieties today have good resistance to Stewart’s wilt, so the disease is not considered a problem. The levels of damage from feeding we have seen is not significant, so we have not recommended any control.
Squash vine borer: Two sites, Cape Elizabeth and Gray, were over the five moth per week threshold, and controls for young summer squash plantings were recommended.
Cucurbit Downy Mildew Alert: We continue to be on alert for this important disease of cucumbers, melons and squash. There have not yet been any confirmed cases in Maine.
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 | 1 | 0 | 34 | 5% | One spray for FAW on silking corn |
| Bowdoinham | 2 | 0 | 2 | 4% | 6-day spray interval recommended for silking corn |
| Cape Elizabeth | 1 | 0 | 5 | 9% | One spray for FAW on silking corn |
| Dayton | 1 | 0 | 2 | 0% | One spray for western bean cutworm (see text above) |
| Durham | 0 | 0 | 1 | One spray for western bean cutworm (see text above) | |
| Farmington | 0 | 1 | 0 | One spray for western bean cutworm (see text above) | |
| Garland | 1 | 2 | 0 | 0% | No spray recommended |
| Gray | 23 | 0 | 29 | 9% | 4-day spray interval recommended for silking corn |
| Lewiston | 0 | 0 | 1 | One spray for western bean cutworm (see text above) | |
| Monmouth | 0 | 0 | 4 | 0% | One spray for FAW on silking corn |
| Oxford | 0 | 4 | 1 | 0% | One spray for western bean cutworm (see text above) |
| Palmyra | 0 | 5 | 0 | 0% | One spray for ECB on silking corn |
| Wayne | 1 | 0 | 3 | 0% | One spray for FAW on silking corn |
| Wells I | 2 | 0 | 0 | 0% | 6-day spray interval recommended for silking corn |
| Wells II | 10 | 2 | 4 | 0% | 4-day spray 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
| 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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