Sweet Corn IPM Newsletter No. 9 — August 21, 2026
Fall Armyworm Threatens Late Corn
Corn Earworm Numbers Lower, Silking Corn Requires Protection
Situation
Most parts of the state are still very dry and irrigation sources are being strained on many farms. Heat and drought have caused some pollination and fill problems with corn ears, especially in unirrigated fields, but later planted corn is mostly looking good. Corn earworm counts were down this week, but still at threatening levels in most sites. Fall armyworm counts were higher at nearly all locations.
European corn borer: Moth counts were low again this week. No sites were over the threshold of five moths in the presence of silking corn. Larval feeding damage in pre-tassel corn was also low. No sprays for corn borer were recommended for corn that is not yet silking.
Corn earworm: Moth counts were lower at nearly all locations this week, although all but two sites are still on a spray interval for silking corn. A 6-day spray interval for silking corn was recommended in Palmyra; A 5-day spray interval was recommended for Bowdoinham, Corinth and Monmouth. A 4-day spray interval was recommended for Biddeford, Cape Elizabeth, Dayton, Durham, Gray, Lewiston, Oxford and Wells. The Farmington and Wayne sites were not over threshold this week.
Fall armyworm: Moth numbers were much higher in pheromone traps at nearly all sites this week, exceeding the threshold of three per week in silking corn at all sites except Palmyra. Two of these locations, Farmington and Wayne, were not presently on a spray interval for corn earworm, so a spray to protect silking corn was recommended. Fall armyworm larval feeding damage in pre-tassel corn was higher at some locations and exceeded the threshold of 12% (for daytime temperatures over 80°) at Cape Elizabeth and Oxford.
Western Bean Cutworm: Moth and egg mass counts were variable this week but continue to decline overall. Gray, Lewiston and Oxford had potentially damaging populations, and a protective silk spray would be recommended if these fields were not presently on a spray program for corn earworm.
Squash vine borer: Moth numbers in pheromone traps continue to be low this week. No sites exceeded the 5-moth threshold.
Aphids: Aphid infestations on tassels and silks continue to be an issue in most fields. Registered insecticides include Assail®, Asana®, Warrior® and Lannate®.
When Should I Stop Spraying: When a silking corn field is under a spray interval for corn earworm, spraying should stop once the silks are thoroughly dried and brown. At this stage, corn earworm moths are unlikely to lay eggs on it. However, if earworm pressure is very high (e.g. 91+ moths per week) and/or fall armyworm moths are over threshold (3 or more moths per week), then spraying should continue until either the moth counts drop, or the required number of days before harvest (dh) for the product being used is reached.
Deep Compost School at Sound Pine Farm:
Join the University of Maine Cooperative Extension and Sound Pine Farm on August 25 for a field day about deep compost mulch soil management for vegetables. Participants will hear about our project, tour Sound Pine Farm’s deep compost mulch fields, and take part in a discussion with fellow farmers and Extension staff. This field day is free to attend, though registration is required. Visit the Deep Compost Mulch Field Day at Sound Pine Farm’s event page for registration and agenda.
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 | 14 | 1 | 59 | 0 | 11% | 4-day spray interval recommended for silking corn |
| Bowdoinham | 7 | 0 | 40 | 2 | – | 5-day spray interval recommended for silking corn |
| Cape Elizabeth | 55 | 3 | 69 | 0 | 17% | 4-day spray interval recommended for silking corn |
| Corinth | 7 | 0 | 15 | – | 1% | 5-day spray interval recommended for silking corn |
| Dayton | 20 | 4 | 4 | 1 | 8% | 4-day spray interval recommended for silking corn |
| Durham | 12 | 0 | 45 | 0 | – | 4-day spray interval recommended for silking corn |
| Farmington | 1 | 0 | 7 | 1 | – | One time spray on silking corn for FAW |
| Gray | 62 | 0 | 65 | 6 | – | 4-day spray interval recommended for silking corn |
| Lewiston | 45 | 1 | 56 | 4 | – | 4-day spray interval recommended for silking corn |
| Monmouth | 7 | 0 | 24 | 1 | – | 5-day spray interval recommended for silking corn |
| Oxford | 11 | 1 | 6 | 4 | 13% | 4-day spray interval recommended for silking corn |
| Palmyra | 3 | 1 | 0 | – | 1% | 6-day spray interval recommended for silking corn |
| Wayne | 1 | 0 | 9 | 2 | – | One time spray on silking corn for FAW |
| Wells | 23 | 0 | 8 | 0 | – | 4-day spray interval recommended for silking corn |
| Wells II | 33 | 1 | 14 | 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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