Sweet Corn IPM Newsletter No. 4 — July 21, 2023


Fall Armyworm Moths and Larvae Found in Several Fields


Japanese beetles eating holes in corn leaves
Japanese Beetle damage on corn; photo by Dr. David Handley

Early planted corn is maturing quickly in southern Maine, with continued warm temperatures. Many fields have soils that are still wet from all the rain, and we continue to see nutrient deficiencies and weed control problems as a result. Insect pests were fairly quiet in cornfields this week, but Japanese beetle populations have been very high in many crops. Squash and pumpkin pests, including squash vine borer, striped cucumber beetle and squash bug have been active.

European corn borer: Very little larval feeding was observed in most fields this week. Only one field in Biddeford was over the control threshold of 15% in pre-tassel stage corn. Moth counts also remained low this week, with one exception in Monmouth, and didn’t present a threat to silking corn.

Corn earworm: With the exception of one site in Garland, corn earworm numbers were fairly low this week. Most, but not all fields with fresh silking corn still require some protection. We saw more earworm feeding on whorl to pre-tassel plants at several sites, which happens when silking corn is not yet available. This damage is counted, along with any borer or armyworm damage, to determine if a pre-silking spray is warranted. Feeding was over the 15% infestation level in pre-tassel corn in Auburn and Cape Elizabeth. A 4-day spray interval for silking corn was recommended for Garland. A 5-day spray schedule was recommended for Biddeford and Lewiston. A 6-day spray interval was recommended for Auburn, Cape Elizabeth and Farmington.

Fall armyworm: Moths were caught in pheromone traps at a few more sites this week and were over the three moth threshold for silking corn in New Gloucester. Low levels of larval feeding damage were found in pre-tassel corn, but not over threshold.

Aphids on the corn silk and husk of plant
Aphids on corn; photo by Dr. David Handley

Corn leaf aphids have been observed in several fields over the past two weeks. Aphids often infest corn plants in fields that have not recently been sprayed for other pests. Colonies of these small, bluish-green insects can cover the tassels, stalks and husks. The waste aphids excrete on the plants, called “honeydew” stimulates the development of sooty mold. This dark, slimy fungus coats the surface of the husks, reducing the marketability of the ears. Sprays applied for corn earworm usually control aphids. Sprays specifically for aphids would only be recommended if sooty mold is becoming a problem.

Squash vine borer: Moth counts were much higher at most locations this week. All sites with traps were over the five moth threshold and sprays are recommended for all pumpkins and susceptible winter and summer squash types. Sprays should be targeted at the base of the plants where the moths lay their eggs. See the New England Vegetable Management Guide for control options.

Spotted wing drosophila alert: We are now catching this insect in berry fields. These flies can cause serious losses to berry crops. For more information visit our Spotted Wing Drosophila Blog.


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259

UMaine Extension Diagnostic
Research Lab, Pest Mgmt. Unit
17 Godfrey Drive
Orono, ME 04473

Sweet Corn IPM Weekly Scouting Summary

Location CEW Moths ECB Moths FAW Moths %Feeding Damage Recommendations / Comments
Auburn 2 0 2 23% 6-day interval recommended for silking corn
Biddeford 4 0 2 28% 5-day interval recommended for silking corn
Bowdoinham 0 0 0 7% No spray recommended
Cape Elizabeth 2 0 0 23% 6-day interval recommended for silking corn
Dayton I 0 0 0 0% No spray recommended
Farmington 2 0 0 2% 6-day interval recommended for silking corn
Garland 31 0 0 1% 4-day interval recommended for silking corn
Lewiston 4 0 1 0% 5-day interval recommended for silking corn
Monmouth 4 14 1 0% No spray recommended (no silking corn)
New Gloucester 0 0 3 0% One spray on silking corn for FAW
Oxford 0 0 0 3% No spray recommended
Palmyra 2 0 0 1% No spray recommended (no silking corn)
Sabattus 0 0 1 3% No spray recommended
Wayne 1 0 0 2% No spray recommended
Wells I 0 0 1 3% No spray recommended
Wells II 1 0 0 5% No spray recommended

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm

Corn Earworm Spray Thresholds for Pheromone Traps

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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