Sweet Corn IPM Newsletter No. 10 — August 28, 2026
Fall Armyworm, Corn Earworm Threaten Late Corn
Silking Corn Requires Protection, Feeding Damage Increasing on Younger Corn
Situation
Corn earworm and fall armyworm moth counts were variable by location this week, but mostly higher and at threatening levels. Powdery mildew and squash bugs are being found in maturing squash and pumpkin fields, and there are recent reports of cucurbit downy mildew in the northeast.
European corn borer: Moth counts were very low 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 very low.
Corn earworm: Moth counts were higher at most locations this week. Only one site (Wayne) is not presently under 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 Farmington. A 4-day spray interval was recommended for Biddeford, Bowdoinham, Cape Elizabeth, Corinth, Dayton, Durham, Gray, Monmouth, Oxford and Wells. A 3-day spray interval was recommended for Lewiston.
Fall armyworm: Moth numbers remain high at nearly all sites this week, exceeding the threshold of three per week in silking corn at all sites except Dayton and Palmyra. Only one of these locations, Wayne, is 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 also higher and exceeded the threshold of 12% (for daytime temperatures over 80°) at Biddeford and Cape Elizabeth.
Western Bean Cutworm: Moth counts were very low this week. Only the site in Gray 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.
Powdery mildew has been found on squash and pumpkin plants around the state this week. There are numerous fungicides available for managing this fungal disease. See the New England Vegetable Management Guide for details. Start fungicide applications when symptoms (gray powdery spots on leaves) are just beginning to develop or when fruit are starting to enlarge. Use a 14-day spray interval with resistant varieties; a 7-day spray schedule with other varieties. Rotate the fungicide family (FRAC group) used often to prevent resistance development.
Cucurbit downy mildew (CDM) Alert: CDM has been reported in Pennsylvania and northern Ohio on cucumber and watermelon. Spores from these areas could soon arrive in New England. Growers should be regularly applying preventative materials (chlorothalonil or copper) and should now add CDM-targeted materials, rotating between different FRAC Groups.
Details about targeted materials can be found on the UMass Vegetable Notes webpage.
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- Cucurbit downy mildew on underside of a cucumber leaf showing dark gray sporulation; posted with permission from UMass Extension.
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- Cucurbit downy mildew on upperside of cucumber leaf; posted with permission from UMass Extension.
Squash bugs are now being found feeding on cucurbit plants around the state. The adults are ½” long dull black bugs. They lay copper colored eggs on the underside of the leaves. The nymphs are smaller, seed-shaped and gray-colored. They feed on the undersides of the leaves and stems of squash and pumpkins, favoring yellow summer squash, Hubbard squash and pumpkins. Feeding can cause the plants to wilt and eventually die. Materials presently registered for squash bugs include Assail®, Brigade®, Asana®, Mustang® and Warrior®. See the New England Vegetable Management Guide for details.
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 | 35 | 0 | 39 | 0 | 72% | 4-day spray interval recommended for silking corn |
| Bowdoinham | 8 | 0 | 47 | 2 | – | 4-day spray interval recommended for silking corn |
| Cape Elizabeth | 69 | 2 | 44 | 0 | 26% | 4-day spray interval recommended for silking corn |
| Corinth | 9 | 0 | 7 | – | 0% | 4-day spray interval recommended for silking corn |
| Dayton | 26 | 0 | 2 | 0 | – | 4-day spray interval recommended for silking corn |
| Durham | 18 | 0 | 54 | 1 | – | 4-day spray interval recommended for silking corn |
| Farmington | 4 | 0 | 7 | 1 | – | 5-day spray interval recommended for silking corn |
| Gray | 18 | 0 | 38 | 4 | – | 4-day spray interval recommended for silking corn |
| Lewiston | 109 | 0 | 11 | 0 | – | 3-day spray interval recommended for silking corn |
| Monmouth | 27 | 0 | 75 | 1 | – | 4-day spray interval recommended for silking corn |
| Oxford | 17 | 1 | 11 | 0 | 1% | 4-day spray interval recommended for silking corn |
| Palmyra | 2 | 0 | 0 | – | – | 6-day spray interval recommended for silking corn |
| Wayne | 0 | 0 | 3 | 0 | – | One time spray on silking corn for FAW |
| Wells | 18 | 0 | 5 | 0 | – | 4-day spray interval recommended for silking corn |
| Wells II | 64 | 1 | 37 | 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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