Sweet Corn IPM Newsletter No. 4 — July 3, 2024


Fall Armyworm, Western Bean Cutworm Numbers Variable


Fall Army Worm on Pre-tassel Corn Plant
Fall Army Worm on Pre-tassel Corn; photo by David Handley

Many early planted fields are coming into silk this week, although there is still plenty of pre-tassel and whorl stage corn from later seedings. The warm weather and adequate water have encouraged rapid growth, and plantings mostly look very good. We found all three of the major sweet corn pests in pheromone traps this week, plus western bean cutworm. Growers with silking corn should be spraying to protect against infestation

European corn borer: Moth counts were over the threshold for silking corn at most locations this week. At sites with silking corn that were not yet spraying for corn earworm, including Farmington, Lewiston and Oxford sprays were recommended. Larval feeding damage in late whorl and pre-tassel continues to be found at most sites, but only one was over the spray threshold of 15% injury.

Corn earworm: Moth captures in pheromone traps were variable this week, with high counts in some locations and no moths in others. More fields are now at silking stage, so more sites are now following spray intervals to protect against infestation. A 6-day spray interval for silking corn was recommended in Garland, Cape Elizabeth and one Wells site; A 5-day spray interval was recommended in Dayton and a 4-day spray interval was recommended in Gray and Lewiston.

Fall armyworm: Trap captures of moths were variable from site to site this week. Two locations, Lewiston and Wells were over the three moth threshold for silking corn in pheromone traps, and sprays were recommended. Both sites were also over threshold for European corn borer in silking corn. We continue to find small amounts of larval feeding damage on pre-tassel corn. Look for large, ragged holes in corn leaves, and sawdust-like waste around the emerging tassels. When this injury is found, it should be combined with any European corn borer injury found. A threshold of 15% of plants with fresh injury is used to determine if a spray should be applied.

Western bean cutworm moth
Western Bean Cutworm Moth; photo by Lindsey Ridlon

Western Bean Cutworm: Moth numbers were slightly higher this week in pheromone traps. We monitor and treat this insect similarly to fall armyworm. Sprays for corn earworm or fall armyworm should protect silking corn from western bean cutworm. The optimal time for controlling the larvae is late pre-tassel to tassel.

Squash vine borer: Moth numbers in pheromone traps continue to be over the control threshold at most locations. Sprays to protect squash plants from egg laying moths were recommended in Lewiston, Oxford, Biddeford and Monmouth. See the New England Vegetable Management Guide for control options.

Spotted Wing Drosophila Alert! Growers who are still harvesting strawberries or beginning harvest of raspberries and blueberries should be on the alert for spotted wing drosophila fruit flies and larvae in ripening fruit. Flies and infested fruit have been found in southern Maine, indicating that growers should be prepared to protect ripening fruit when adults are first caught in traps or any infested fruit is found in a field. For more information visit our Spotted Wing Drosophila blog.

Save the date!

University of Maine Highmoor Farm Field Day: Wednesday, July 24. Orchard tours and tree fruit program 1-5 pm; Vegetable and berry tour 5-7 pm. Follow the event’s website for registration information.



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 Management Unit
17 Godfrey Drive
Orono, ME 04473

Sweet Corn IPM Weekly Scouting Summary

Location CEW Moths ECB Moths FAW Moths %Feeding Damage Recommendations / Comments
Biddeford 1 9 1 18% 1 spray for ECB feeding on pre-tassel corn
Bowdoinham 0 0 1 6% No spray recommended
Cape Elizabeth 3 8 0 8% 6-day spray interval for silking corn
Dayton 4 7 0 6% 5-day spray interval for silking corn
Farmington 1 9 1 13% 1 spray for ECB feeding on silking corn
Garland 2 0 0 0% 6-day spray interval for silking corn
Gray 12 6 0 3% 4-day spray interval for silking corn
Lewiston 8 1 0 3% 4-day spray interval for silking corn
Lewiston II 1 5 3 2% 1 spray for FAW + ECB feeding on silking corn
Oxford 0 7 0 6% 1 spray for ECB feeding on silking corn
Wayne 0 0 0 0% No spray recommended
Wells I 0 6 8 14% 1 spray for FAW + ECB feeding on silking corn
Wells II 3 19 2 6% 6-day spray interval for silking corn

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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