Sweet Corn IPM Newsletter No. 8 — August 22, 2025
CORN EARWORM PRESSURE HIGHER
Fall Armyworm Counts Also Higher This Week
Situation
There has been no relief from drought conditions in most of southern and coastal Maine this week. Farmers continue to irrigate whenever and wherever possible, but many face depleting water resources. Poor tip fill, ear size and other quality issues can result from drought stress. Corn earworm and fall armyworm numbers have risen slightly but are still moderate for this late in the season. Aphids have become a concern in most fields, covering the tassels and husks.
European corn borer: There has been a little rise in moth numbers at most locations this week, suggesting that a second generation of corn borer is underway. Silking corn can be threatened by corn borer, but sprays for corn earworm and fall armyworm should provide adequate protection. None of the sites reached the 5 moth threshold to protect silking corn this week.
Corn earworm: Moth numbers were variable from site to site this week, but generally moderate for this late in the season. Dry weather continues to slow the movement of earworm moths into Maine. A six-day spray interval was recommended for Bowdoinham, Corinth, Dayton, and Lewiston. A five-day spray interval for silking corn was recommended for Gray; a four-day spray interval was recommended for Biddeford and one Wells site.
Fall armyworm: Moths counts in pheromone traps exceeded the control threshold (3) for silking corn in Cape Elizabeth, Corinth, Durham, Gray, Wells and Monmouth this week. Sprays to protect silking corn were recommended at Wells, Cape Elizabeth, Farmington, and Monmouth where sites were not under a spray interval for earworm. Armyworm feeding damage on pre-tassel corn was higher at some locations. Sprays were recommended at Biddeford, Bowdoinham, Oxford and Cape Elizabeth where damage exceeded the threshold of 15%.
Western Bean Cutworm: Depending on location, moth counts ranged from 0 to 11 in our pheromone traps this week, as it appears that the peak flight of this pest is over for the season. 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 Wayne.
Aphids and wasps: Aphids have recently been observed infesting the tassels and silks in most fields. This week we observed aphids spreading onto the husks, causing sooty mold due to the honeydew excretions of the aphid. In addition, wasps have been found feeding on the honeydew in tassels and on husks, creating a hazard for harvesters. Insecticides that target aphids include Assail®, Asana®, Warrior® and Lannate®.
Squash vine borer: No sites exceeded the five moth per week threshold this week.
Downy Mildew Alert: Downy mildew has just been confirmed on kale in Maine. Keep a look out for symptoms on this and other cole crops. See the New England Vegetable Management Guide for management options.
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 | 8 | 2 | 2 | 17% | 4-day spray interval recommended for silking corn |
| Bowdoinham | 2 | 1 | 19% | 6-day spray interval recommended for silking corn | |
| Cape Elizabeth | 1 | 2 | 6 | 48% | One spray for FAW on silking corn and pre-tassel corn |
| Corinth | 2 | 3 | 16 | 3% | 6-day spray interval recommended for silking corn |
| Dayton | 2 | 0 | 6% | 6-day spray interval recommended for silking corn | |
| Durham | 4 | 0 | 10 | 5-day spray interval recommended for silking corn | |
| Farmington | 0 | 1 | 3 | One spray for FAW on silking corn | |
| Gray | 6 | 0 | 44 | 5-day spray interval recommended for silking corn | |
| Lewiston | 2 | 4 | 2 | 6-day spray interval recommended for silking corn | |
| Monmouth | 1 | 0 | 4 | 0% | One spray for FAW on silking corn |
| Oxford | 0 | 4 | 1 | 15% | One spray for FAW feeding injury |
| Wayne | 1 | 1 | 2 | 0% | One spray for western bean cutworm (see text above) |
| Wells I | 1 | 0 | 3 | One spray for FAW on silking corn | |
| Wells II | 11 | 2 | 13 | 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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