Sweet Corn IPM Newsletter No. 2 — July 11, 2025
SWEET CORN PESTS ACTIVE!
Early Silking Corn Needs Protection
SITUATION
Warm weather has pushed corn development rapidly across the state. Early plantings are now in silk in many locations. All of the major corn pests are active, but populations are variable from location to location. Corn earworm, fall armyworm and European corn borer have all been over the control threshold at different locations.
European Corn Borer: Moths caught in pheromone traps were over threshold (5) for silking corn in Biddeford and Dayton this week, but the Biddeford site does not yet have silking corn and the Dayton site is also on a spray schedule for corn earworm, so no additional sprays were required. We have found larval feeding in late whorl and pre-tassel corn at most sites. Only pre-tassel fields in Biddeford, Farmington and Gray exceeded the recommended spray threshold of 15% injury, so single sprays were recommended at those sites (see table below).
Growers should start scouting pre-tassel stage corn for feeding injury now. Varieties of corn genetically modified to produce the Bt toxin (e.g. Bt corn, Attribute® varieties), shouldn’t need to be sprayed for European corn borer.
Corn earworm: Moths were caught in most locations this week, but this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths are caught at a site, all silking corn in the fields should be protected with regular sprays, following the recommended intervals in the table below. This week, a six-day spray interval for silking corn was recommended for Garland, Lewiston, Wayne, and one Wells site. A five-day spray interval was recommended for our site in Dayton.
Fall armyworm: Moths were caught in pheromone traps at most locations this week, but we have only found minor feeding damage in the field so far. For silking corn, a three-moth per week threshold is used to prevent larvae from moving directly into the ears. Biddeford and Gray exceeded the threshold, but there is not yet silking corn at the Biddeford site. Often fall armyworm is present at the same time as corn earworm and the spray program for corn earworm will control both insects.
Squash vine borer: The five moth per week threshold was exceeded at all locations except Farmington this week, indicating that this insect is now very active in squash and pumpkin fields. Squash vine borer moths are black and orange and resemble wasps. They lay their eggs at the base of squash plants. The larvae bore into the base of the plants, causing vines to wilt and collapse. Growers should protect all summer squash, winter squash and pumpkins now to prevent infestation. Butternut squash, cucumbers are not susceptible. See the New England Vegetable Management Guide for control options.
Spotted Wing Drosophila (SWD) Alert: We are starting to catch SWD in traps this week. See the SWD Alert for more information.
Sincerely,
David T. Handley
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 | 1 | 0 | 1 | 6% | No spray recommended |
| Biddeford | 1 | 12 | 5 | 22% | One spray for ECB and FAW feeding damage |
| Bowdoinham | 1 | 0 | 0 | 5% | No spray recommended |
| Cape Elizabeth | 1 | 0 | 0 | 7% | No spray recommended |
| Dayton | 4 | 13 | 1 | 1% | 5-day spray interval for silking corn |
| Farmington | 0 | 0 | 1 | 17% | One spray for ECB feeding damage |
| Garland | 3 | 0 | 0 | 0% | 6-day spray interval for silking corn |
| Gray | 0 | 0 | 3 | 17% | One spray for ECB feeding damage and FAW moths |
| Lewiston | 2 | 0 | 1 | 7% | 6-day spray interval for silking corn |
| Monmouth | 0 | 0 | 2 | No spray recommended | |
| Oxford | 0 | 1 | 0 | 2% | No spray recommended |
| Wayne | 2 | 0 | 0 | 9% | 6-day spray interval for silking corn |
| Wells I | 3 | 2 | 0 | 6% | 6-day spray interval for silking corn |
| Wells II | 0 | 4 | 2 | 1% | No spray recommended |
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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