Sweet Corn IPM Newsletter No. 9 — August 29, 2025
PEST PRESSURE FOR LATE CORN MODERATE
Labor Day Supply Looks Good Despite Drought
Situation
Despite little to no relief from the drought throughout the state this week, most farmers are going into the Labor Day weekend with a good supply of corn with good quality. Later planted corn has matured rapidly under warm growing conditions to fill gaps created by earlier planted corn that germinated poorly. Corn earworm and fall armyworm numbers remain moderate for this late in the season, although counts have been more variable from site to site this week. Aphids continue to be a concern in most fields, covering the tassels and husks, and attracting wasps.
European corn borer: Moths counts were lower this week, with most sites not catching any in our traps. None of the sites reached the 5 moth threshold to protect silking corn.
Corn earworm: Moth numbers were mostly moderate but variable from site to site this week. There appears to be little movement of moths coming into the state from southern locations. A six-day spray interval for silking corn was recommended for Biddeford, Bowdoinham, Durham, Wayne, and one Wells site. A five-day spray interval was recommended for Corinth and Dayton; a four-day spray interval was recommended for Cape Elizabeth.
Fall armyworm: Moths counts in pheromone traps exceeded the control threshold (3) for silking corn in Cape Elizabeth, Corinth, and one Wells site. These sites are under a spray schedule for earworm so no additional sprays were recommended. Armyworm feeding damage on pre-tassel corn exceeded the threshold of 15% and sprays were recommended at Bowdoinham and Wells.
Western Bean Cutworm: Moths (3) were only caught at one Wells site this week. A single spray was recommended for silking corn.
Aphids: Aphid infestations on tassels and silks continue to be an issue in most fields. If sooty mold is becoming an issue on husks, sprays targeting aphids should be considered. Insecticides registered for aphids on corn include Assail®, Asana®, Warrior® and Lannate®.
Squash vine borer: No sites exceeded the five moth per week threshold this week.
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.
Birds, etc.: Flocking species of blackbirds are starting to cause damage in cornfields around the state. They are especially attracted to fields where corn has been allowed to get over-mature. Deer, skunks and raccoons have also been troublesome this year. For information on wildlife problems and management options, you may call the Animal and Plant Health Inspection Service (APHIS) office in Augusta at 1-866-487-3297.
Vegetable and Small Fruit Growers Twilight Meeting: Clark Farms in Jefferson, Maine is hosting the meeting on Tuesday, September 16 at 5:30 p.m. For more information, contact the Maine Vegetable and Small Fruit Growers Association.
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 | 3 | 0 | 1 | 10% | 6-day spray interval recommended for silking corn |
| Bowdoinham | 2 | 0 | 0 | 16% | 6-day spray interval recommended for silking corn |
| Cape Elizabeth | 8 | 0 | 21 | 7% | 4-day spray interval recommended for silking corn |
| Corinth | 5 | 2 | 20 | 2% | 5-day spray interval recommended for silking corn |
| Dayton | 7 | 0 | 0 | 0% | 5-day spray interval recommended for silking corn |
| Durham | 3 | 0 | 1 | 6-day spray interval recommended for silking corn | |
| Farmington | 0 | 0 | 0 | One spray for WBCW on silking corn (see text above) | |
| Monmouth | 0 | 0 | 0 | No spray recommended | |
| Oxford | 0 | 1 | 1 | 8% | No spray recommended |
| Wayne | 3 | 0 | 1 | 6-day spray interval recommended for silking corn | |
| Wells I | 1 | 0 | 0 | No spray recommended | |
| Wells II | 2 | 0 | 6 | 19% | 6-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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