Sweet Corn IPM Newsletter No. 11 – September 11, 2020

Last Issue for 2020

Click on photos to enlarge.

Sweet Corn IPM Newsletter No. 11 – September 11, 2020Sweet Corn


Fall Armyworm Still Threatens Late Maturing Corn in Many Fields

This will be the final issue of the Sweet Corn IPM Newsletter for the 2020 season. I would like to thank all of the growers who participated in the program this year, and our team of IPM scouts, including: Lindsey Ridlon, Kara Rowley and Sean McAuley. Special thanks to Caitlin Ramsay for taking over the editing and mailing of the newsletter under very challenging circumstances this season.



Corn sales were good on Labor Day, as they have been through the season.  Although demand typically drops off after the holiday, the strong farm stands sales this year may buck that trend somewhat, if fresh corn is still available.  Many fields are still dry, but ear quality has mostly been very good.  Pest pressure increased this week, with jumps in both corn earworm and fall armyworm numbers, likely due to warm fronts coming up from the south and higher night temperatures.


European Corn Borer Larva on Ear
European Corn Borer Larva on Ear, photo by David Handley



European corn borer:

It doesn’t appear that a partial second-generation, that was seen in some locations, gained any traction. Larval feeding injury was not over the 15% control threshold for pre-silking corn, and moth counts were not over the weekly threshold of five for silking corn at any site this week.





Corn Earworm Moth
Corn Earworm Moth; photo by David Handley

Corn earworm:

Moth captures increased significantly in some sites this week, while others continued to see low numbers. A four-day interval for silking corn was recommended at Biddeford, Cape Elizabeth, one Dayton site, New Gloucester, Poland Spring, Wayne and one Dayton site. A six-day spray interval was recommended at one Dayton site, and one Wells site.



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

Fall armyworm (FAW):

Moth captures increased at most locations and were over threshold at nearly all sites, including: Biddeford, Bowdoinham, Cape Elizabeth, Dayton, New Gloucester, Oxford, Wayne and Wells. The  Bowdoinham, Oxford and Wells sites were not also under a spray interval for corn earworm, so sprays were recommended for silking corn.



Annual End of Corn Season Checklist:

  1. Plow down corn stalks and stubble to destroy overwintering larvae of European corn borer
  2. Plant a cover crop, such as winter rye, to prevent soil erosion and to add organic matter to the soil.
  3. Take a soil test to determine if lime or other nutrients should be applied.
  4. Plan to rotate your crops to prevent pests from building up in any one location.
  5. Review weed control; what worked and what didn’t? What were the problem weeds? Match herbicides and cultivation practices for those next year.
Drosophila Trap
Drosophila Trap, photo by David Handley


Spotted wing drosophila:

Trap counts have been very high at nearly all locations, 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




David T. Handley

Vegetable & Small Fruit Specialist

Highmoor Farm                      Pest Mgmt. Unit

P.O. Box 179                            17 Godfrey Drive

52 U.S. Route 202                   Orono, ME  04473

Monmouth, ME  04259          1.800.287.0279


Sweet Corn IPM Weekly Scouting Summary

Location CEW






Recommendations / Comments
Biddeford 10 1 35 4-day spray interval for all silking corn
Bowdoinham 0 18 One spray on silking corn for FAW
Cape Elizabeth I 19 0 27 4-day spray interval for all silking corn
Cape Elizabeth II 25 0 18 4-day spray interval for all silking corn
Dayton I 18 0 7 4-day spray interval for all silking corn
Dayton II 2 0 14 6-day spray interval for all silking corn
New Gloucester 44 0 11 4-day spray interval for all silking corn
Oxford 0* 0 12 One spray on silking corn for FAW (*Trap down)
Poland Spring 50 0 2 4-day spray interval for all silking corn
Sabattus 0 0 0* No spray recommended (*Trap down)
Wayne 38 2 24 4-day spray interval for all silking corn
Wells I 3 4 6-day spray interval for all silking corn
Wells II 0 0 24 One spray on silking corn for FAW

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 the 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 :

UMaine IPM

Pest Watch



Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.


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