Sweet Corn IPM Newsletter No. 2 – July 10, 2020

Sweet Corn

Sweet Corn IPM Newsletter No. 2 –  July 10, 2020

Click on photos to enlarge.


Early-Planted Fields Now Silking May Require Protection



Recent warm weather and rain showers have advanced corn development rapidly in much of the state. Earliest planted corn with plastic mulch or rowcovers in southern Maine is starting to silk. Both corn earworm and fall armyworm have arrived just in time to threaten this early silking corn, and European corn borer is active in younger corn. While the greatest threat now is to silking corn, both European corn borer and fall armyworm can cause significant injury to younger plant stages as well. Warm temperatures, predicted for the days ahead, will likely increase insect activity, so growers with silking corn should consider protecting it.

European corn borer:

European Corn Borer Larvae on Pre-tassel Stage Corn
European Corn Borer Larvae on Pre-tassel Stage Corn; photo by David Handley

Larval feeding injury was over the 15% control threshold for pre-tassel corn in Biddeford, Poland Spring, and Sabattus. Sprays during the pre-tassel stage, when both moths and larvae are present, can control larvae before they move into the stalks and ears where they will be protected. Once corn reaches the silk stage, sprays may be based on the number of moths caught in pheromone traps. Moths will lay eggs on flag leaves of silking corn, and the larvae can move into the ears without leaving visible feeding injury. If more than five moths are caught during a week in silking corn, a spray is recommended. However, no European corn borer trap counts were over the spray threshold for silking corn this week.

Corn earworm:

Corn Earworm Moth
Corn Earworm Moth; photo by David Handley

We caught earworm moths in most locations throughout the state this week.  These moths will lay eggs on fresh silking corn, so early fields with silking corn should be protected. The recommended frequency of sprays depends on the number of moths present at a site. More moths will require more frequent sprays to provide good control. A six-day spray interval for silking corn was recommended in Bowdoinham, New Gloucester and Sabattus.  A five-day spray interval was recommended for a silking field in Lewiston this week.

Fall armyworm:

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


The first moths were caught in pheromone traps this week, creating a threat to silking corn, although most captures were below the three moth threshold for silking corn.  A small amount of larval feeding damage was also noticed on pre-tassel corn, suggesting that this will become a more widespread problem soon. A spray to protect silking corn against fall armyworm was recommended in Poland Spring. This site is not under a spray interval for corn earworm yet, so a spray specifically for fall armyworm is warranted.



Squash vine borer

Three Squash Vine Borer Moths
Three Squash Vine Borer Moths; photo by Lindsey Ridlon

moths are being caught in high numbers in New Hampshire this week. We have set up traps at several locations, and will have data from them next week.  However, growers in southern Maine should scout squash and pumpkin fields for squash vine borer feeding at the base of the plants and/or wilting vines now, and apply appropriate control if damage is found. Squash vine borer moths are black and orange and resemble wasps. They lay their eggs at the base of squash plants. The larvae bore into the base of the plants, causing vines to wilt and collapse. See the 2020-2021 New England Vegetable Management Guide for control options.



David T. Handley

Vegetable and Small Fruit Specialist


Highmoor Farm                     UMaine Extension Diagnostic

P.O. Box 179                          Research Lab, Pest Mgmt. Unit

52 U.S. Route 202                 17 Godfrey Drive

Monmouth, ME  04259         Orono, ME  04473

207.933.2100                          1.800.287.0279


Sweet Corn IPM Weekly Scouting Summary

Location CEW








Recommendations / Comments
Biddeford 0 0 2 22% One spray for ECB, FAW on pre-tassel corn
Bowdoinham 2 1 0 8% 6-day spray interval for silking corn
Cape Elizabeth I 0 0 0 1% No spray recommended
Dayton I 1 0 0 1% No spray recommended
Farmington 0 0 0 2% No spray recommended
Lewiston 0 4 0 4% No spray recommended
Lewiston II 4 0 0 0% 5-day spray interval for all silking corn
Monmouth 1 0 1 4% No spray recommended
New Gloucester 2 0 2 0% 6-day spray interval for all silking corn
Oxford 0 0 1 1% No spray recommended
Poland Spring 0 3 4 30% One spray for ECB & FAW on pre-tassel – silking corn
Sabattus 2 0 0 16% 6-day spray interval for silking corn, 1 spray for ECB
Wayne 0 0 0 2% No spray recommended
Wells I 1 0 0 3% No spray recommended
Wells II 0 0 1 3% 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:

Integrated Pest Management in Maine

Integrated Pest Management Data Visualization Tool

UMass Cooperative Extension Website

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