Sweet Corn IPM Newsletter No. 4 — July 25, 2025
CORN EARWORM PRESSURE INCREASES
Silking Corn Should Be Under A Protective Spray Schedule
SITUATION
Early sweet corn harvest has begun in southern Maine and will be in full swing by next week. Reports so far indicate that quality has been mostly very good and demand is strong. High temperatures continue to drive rapid development of later corn, and growers are irrigating wherever possible to avoid drought stress. Corn earworm emerged as the most important pest issue in corn this week with nearly all monitoring sites now on a recommended spray schedule to protect fresh silking corn.
European Corn Borer: Moth counts were very low this week, suggesting that the first generation of this pest is likely over. A partial second generation is not uncommon, and usually emerges in late August. Trap captures of moths did not exceed the control threshold (5) for silking corn at any location. However, there are still larvae actively feeding in fields, and scouting for damage should continue. We found feeding damage in pre-tassel corn at most sites, but none of it exceeded the recommended spray threshold of 15% injury (see table below).
Corn earworm: Moth numbers were up at nearly all locations, this week, requiring protection of all fresh silking corn to prevent infestation. A four-day spray interval for silking corn was recommended for Auburn, Biddeford, Bowdoinham, Cape Elizabeth, and Dayton; a five-day interval was recommended for Gray, Lewiston, Oxford, Wayne and Wells; a six-day spray interval was recommended for Monmouth and Garland. 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 Auburn, Biddeford and Cape Elizabeth this week, but all of these sites are presently under a spray schedule for corn earworm, so no additional sprays should be required. Armyworm feeding damage was generally low this week indicating that pre-tassel sprays are being effective in managing earlier infestations. None of the sites scouted exceeded the control threshold of 15% injury.
Western Bean Cutworm: Depending on location, moth counts ranged from 0 to 15 in our pheromone traps this week, with the highest counts generally being in the southern and western parts of the state. The highest moth count was in Farmington, where silking fields are not presently under a spray interval for corn earworm, so a spray was recommended. Typically, sprays for corn earworm should protect silking corn from western bean cutworm.
Squash vine borer: A spray for vine borer was recommended only in one field in Gray this week. All other locations saw populations drop below the five moth per week threshold, suggesting the first generation of squash vine borer may be coming to an end for this season. A second generation sometimes occurs in early September.
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 |
|---|---|---|---|---|---|
| Auburn | 8 | 0 | 4 | 1% | 4-day spray interval recommended for silking corn |
| Biddeford | 11 | 0 | 18 | 14% | 4-day spray interval recommended for silking corn |
| Bowdoinham | 10 | 0 | 0 | 9% | 4-day spray interval recommended for silking corn |
| Cape Elizabeth | 14 | 0 | 20 | 4% | 4-day spray interval recommended for silking corn |
| Dayton | 13 | 0 | 1 | 0% | 4-day spray interval recommended for silking corn |
| Farmington | 0 | 0 | 0 | 0% | One spray for western bean cutworm (see text above) |
| Garland | 0 | 1 | 0 | 0% | 6-day spray interval recommended for silking corn |
| Gray | 7 | 0 | 1 | 3% | 5-day spray interval recommended for silking corn |
| Lewiston | 4 | 0 | 1 | 3% | 5-day spray interval recommended for silking corn |
| Monmouth | 2 | 0 | 3 | 0% | 6-day spray interval recommended for silking corn |
| Oxford | 5 | 0 | 0 | 0% | 5-day spray interval recommended for silking corn |
| Palmyra | 0 | 0 | 0 | 0% | No spray recommended |
| Wayne | 5 | 0 | 1 | 6% | 5-day spray interval recommended for silking corn |
| Wells I | 5 | 0 | 0 | 5% | 5-day spray interval recommended for silking corn |
| Wells II | 4 | 0 | 2 | 2% | 5-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
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.
The University of Maine System is an equal opportunity institution committed to nondiscrimination.