Sweet Corn IPM Newsletter No. 6 — July 31, 2026
Corn Earmworm Populations Very High
Western Bean Cutworm Numbers Also Higher, Threaten Silking Corn
Situation
Corn harvest is well underway in most of the state. Quality and demand have been very good according to most farmers we’ve talked with. The most pressing issue for now is the lack of substantial rainfall. Many fields are drought-stressed, and keeping irrigation flowing has become a major chore. Corn earworm numbers were very high in all locations this week, and western bean cutworm counts continue to rise. Therefore, most fields now require protection for silking corn.
European corn borer: Only one moth was caught this week, so no sites exceeded the threshold for silking corn (5). No ECB larval feeding damage was found.
Corn earworm: Moth counts were much higher this week, exceeding the spray threshold for silking corn at all locations, and putting most farms on a very tight spray interval for good silk protection. We don’t typically see populations this high unless we have had a tropical weather system come up from the south. A 6-day spray interval for silking corn was recommended in Palmyra; A 5-day spray interval was recommended in Oxford. A 4-day spray interval was recommended for Dayton, Garland, Farmington and Gray. A 3-day spray interval was recommended in Biddeford, Bowdoinham, Cape Elizabeth and Lewiston.
Fall armyworm: Moth numbers in pheromone traps were higher at some locations this week, exceeding the threshold of three per week in silking corn at Biddeford, Gray and Monmouth. All of these locations are either on a spray schedule for corn earworm, which should also control fall army worm, or do not yet have silking corn. Fall armyworm larval feeding damage was generally light and not over the recommended spray threshold.
Western Bean Cutworm: Moth and egg mass counts were higher at nearly all locations where we have pheromone traps, and a protective silk spray would be recommended, but all of these fields are presently on a spray program for corn earworm, which should protect silking corn from western bean cutworm as well. We did find some larval feeding injury, but none yet exceeding the spray threshold for pre-tassel corn.
Squash vine borer: Moth numbers in pheromone traps continued to fall this week. No sites were over the control threshold. This may be the end of the squash vine borer threat for the season, but occasionally we do see a small second generation toward the end of the summer.
Corn leaf aphids have been observed in several fields. 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.
Save the Date!
New England Vegetable and Fruit Conference, will take place at the Double Tree in Manchester, New Hampshire. The conference offers 3 days of talks, covering several crops and topics, farmer to farmer sessions and more. Dates for the conference are December 15, 16, 17, 2026.
Registration and schedule information can be found on the New England Vegetable and Fruit Conference website.
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 | WBCW Moths | % Feeding Damage | Recommendations / Comments |
|---|---|---|---|---|---|---|
| Biddeford | 114 | 0 | 3 | 10 | 8% | 3-day spray interval recommended for silking corn |
| Bowdoinham | 156 | 0 | 2 | 27 | 1% | 3-day spray interval recommended for silking corn |
| Cape Elizabeth | 141 | 0 | 1 | 9 | 10% | 3-day spray interval recommended for silking corn |
| Dayton | 65 | 0 | 1 | 15 | 2% | 4-day spray interval recommended for silking corn |
| Farmington | 15 | 0 | 0 | 39 | 2% | 4-day spray interval recommended for silking corn |
| Garland | 21 | 0 | 0 | 4-day spray interval recommended for silking corn | ||
| Gray | 37 | 1 | 10 | 39 | 0% | 4-day spray interval recommended for silking corn |
| Lewiston I | 126 | 0 | 0 | 79 | 0% | 3-day spray interval recommended for silking corn |
| Lewiston II | 132 | 0 | 0 | 13 | 3% | 3-day spray interval recommended for silking corn |
| Monmouth | 27 | 0 | 5 | 22 | 0% | No spray recommended (no silking corn) |
| Oxford | 7 | 0 | 0 | 39 | 2% | 5-day spray interval recommended for silking corn |
| Palmyra | 3 | 0 | 0 | 6-day spray interval recommended for silking corn | ||
| Wells | 15 | 0 | 0 | 0 | 5% | 4-day spray interval recommended for silking corn |
| Wells II | 22 | 0 | 0 | 10 | 3% | 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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