Sweet Corn IPM Newsletter No. 12- September 17, 2021

Sweet Corn
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Sweet Corn IPM Newsletter No. 12- September 17, 2021

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Dried Silks Mean Fields No Longer Attractive For Earworm Moth Egg Laying

This will be the final issue of the Sweet Corn IPM Newsletter for the 2021 season. I would like to thank all of the growers who participated in the program this year, and our team of IPM scouts, including Brooke Martin, Lee Lavoie and Sean McAuley. Special thanks to Caitlin Ramsay for editing and mailing the newsletter and updating our website and blog.



Harvest is coming to a close in many fields this week, although a few late planted fields may extend the season a little longer. Most corn remaining is no longer attractive to earworm for egg-laying (dried, brown silks), although fall armyworm could still be an issue as larvae can chew into ears from the sides. Moth counts were generally lower this week, as cooler night temperatures reduced activity, and the expected bump in populations from the recent tropical storm never occurred.


European Corn Borer Moth
European Corn Borer Moth; photo by David Handley


European corn borer:

Fields being sprayed for corn earworm and/or fall armyworm are not scouted for corn borer, as they will be controlled by those insecticide applications. Moth populations were low at all locations; none exceeded the 5 moths/week threshold for silking corn.



Corn Earworm Feeding on Corn
Corn Earworm Feeding on Corn; photo by David Handley




Corn earworm:  

Pheromone trap moth captures were lower in most sites this week, as cooler night temperatures have slowed activity, and most fields no longer have fresh silk available for egg laying. A 4-day spray schedule was recommended for fresh silking corn in Biddeford, Cape Elizabeth, New Gloucester and one Dayton site.  A 5-day spray schedule was recommended for Auburn, Corinth and one Dayton site.  A 6-day spray interval was recommended for Bowdoinham and one Wells site.  Fields in which the silks are brown and dry need not be sprayed for corn earworm.



Male Fall Armyworm Moth
Male Fall Armyworm Moth; photo by David Handley



Fall armyworm:

Moth counts exceeded the 3 moths/ week threshold for silking corn at sites in Auburn, Biddeford, Cape Elizabeth, and one Dayton site. All sites are on a recommended spray schedule for corn earworm, which should provide protection against fall armyworm.


Drosophila Trap
Drosophila Trap, photo by David Handley



Spotted wing drosophila:

Trap counts have been very high at all locations this week, meaning there is a very high threat level for any ripening fruit remaining in berry fields. Growers should maintain a tight, regular (5-7 day) spray schedule to prevent larvae from infesting fruit. For more information visit our website



Corn Field Plowed Down
Corn Field Plowed Down; photo by David Handley

Maintaining soil health for next season

Plowing down corn stalks after the season can help reduce overwintering European corn borer, but can also lead to significant soil erosion. Planting winter rye after harvest can produce enough of a vegetative cover to prevent erosion. Given the abundant rainfall this year, a modest nitrogen fertilizer application (30-50 lb. N/A) may be needed to get a good stand establishment; don’t rely on nitrogen leftover from the corn crop.  Applying manure in the fall can also be useful for soil building and fertility but it should be applied and incorporated before the soil freezes, or by December 1st at the latest.



David T. Handley

Vegetable & Small Fruit Specialist

Highmoor Farm            Pest Management Unit

P.O. Box 179                 17 Godfrey Drive

52 U.S. Route 202         Orono, ME  04473

Monmouth, ME  04259

207.933.2100                 1.800.287.0279


Sweet Corn IPM Weekly Scouting Summary

Location CEW






Recommendations / Comments
Auburn 4 0 3 5-day spray interval for silking corn
Biddeford 8 0 3 4-day spray interval for silking corn
Bowdoinham 3 0 1 6-day spray interval for silking corn
Cape Elizabeth 24 0 11 4-day spray interval for silking corn
Corinth 6 0 1 5-day spray interval for silking corn
Dayton I 27 1 2 4-day spray interval for silking corn
Dayton II 5 0 12 5-day spray interval for silking corn
Monmouth 0 3 0 No spray recommended
New Gloucester 16 0 2 4-day spray interval for silking corn
Oxford 0 0 2 No spray recommended
Wayne 0 0 1 No spray recommended
Wells I 0 0 0 No spray recommended
Wells II 2 1 0 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:


Pest Watch



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