Sweet Corn IPM Newsletter No. 9 — August 25, 2023
CORN EARWORM PRESSURE GROWS
Fresh Silking Corn Remaining Requires Protection
SITUATION
Last week’s storms appear to have brought up a wave of corn earworm moths, as numbers climbed in most locations this week. Other pest numbers have been lower in most fields, with the exception of four-legged species. Deer, raccoons, skunks and coyotes have been problematic at many sites.
European corn borer: Most fields are in silk or beyond at this point, so we have not been field scouting, unless a field is not under a spray schedule for corn earworm. Counts were over the 5-moth/week threshold for silking corn in Biddeford, Bowdoinham, Dayton, Oxford and one Wells site, where a partial second generation appears to be underway.
Corn earworm: Moth counts were again higher in nearly all locations this week. Based on this week’s moth counts, a 3-day spray interval for silking corn was recommended for Cape Elizabeth, A 4-day spray schedule was recommended for Auburn, Biddeford, Bowdoinham, Dayton, Garland, Lewiston, Monmouth, New Gloucester, Oxford and Wells. A 6-day spray interval was recommended for Palmyra.
Fall armyworm: Moth counts were low at most sites this week. Biddeford, Garland, Monmouth, and New Gloucester were over the three-moth threshold for silking corn.
Western Bean Cutworm: Moth numbers were generally low this week, suggesting that this pest may no longer be a threat in most locations for the remainder of the season. Populations of this pest tend to drop off very rapidly toward the end of August.
Cucurbit downy mildew alert: With ongoing moist weather there continues to be a high risk for cucurbit downy mildew. The strains presently being found in Maine primarily infect cucumber, cantaloupe, and cabbage family crops. Producers of these crops should apply protectant fungicides prior to any future storms. These are listed in the New England Vegetable Management Guide. Chlorothalonil or copper products are protectant fungicides that most growers probably already have on-hand. It may be worth switching to fungicides with specific activity against CDM. They can also be found in the New England Vegetable Management Guide. There have not yet been reports of the strain of downy mildew that affects pumpkins and winter squash in Maine. However, it is important to monitor your crops regularly, and keep an eye out for symptoms of CDM. Excellent photos and more information about this disease can be found here: Cornell Vegetables — Cucurbit Downy Mildew.
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 | 32 | 0 | 0 | — | 4-day interval recommended for silking corn |
| Biddeford | 54 | 13 | 8 | — | 4-day interval recommended for silking corn |
| Bowdoinham | 28 | 8 | 1 | — | 4-day interval recommended for silking corn |
| Cape Elizabeth | 100 | 3 | 0 | — | 3-day interval recommended for silking corn |
| Dayton | 86 | 42 | 1 | — | 4-day interval recommended for silking corn |
| Farmington | 0 | 0 | 1 | — | No spray recommended |
| Garland | 51 | 0 | 7 | 1% | 4-day interval recommended for silking corn |
| Hollis | 0 | 0 | 0 | — | No spray recommended |
| Lewiston | 32 | 0 | 1 | — | 4-day interval recommended for silking corn |
| Monmouth | 49 | 4 | 10 | — | 4-day interval recommended for silking corn |
| New Gloucester | 58 | 0 | 13 | — | 4-day interval recommended for silking corn |
| Oxford | 25 | 6 | 2 | — | 4-day interval recommended for silking corn |
| Palmyra | 2 | 0 | 0 | — | 6-day interval recommended for silking corn |
| Wayne | 1 | 4 | 0 | — | No spray recommended |
| Wells I | 42 | 0 | 0 | — | 4-day interval recommended for silking corn |
| Wells II | 62 | 8 | 1 | 7% | 4-day 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 Data Visualization Tool — Penn State
Integrated Pest Management — UMass Amherst
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