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Sweet Corn IPM Newsletter No. 1 – June 27, 2013

Sweet Corn IPM Newsletter No. 1 – June 27, 2013

For full page print version, please see link at the bottom. Click on photos to enlarge.


Corn Earworm, European Corn Borer Moths Active, Larvae Feeding in Early Corn

The 2013 University of Maine Cooperative Extension Integrated Pest Management (IPM) program for sweet corn is underway. More than twenty volunteer farms are serving as pest monitoring and demonstration sites, with fields in North Berwick, Wells, Dayton, Cape Elizabeth, New Gloucester, Poland Spring, Auburn, Lewiston, Sabattus, Nobleboro, Warren, Monmouth, Wales, Wayne, Oxford, Farmington, Levant, Stillwater, Garland and East Corinth. Pheromone traps have been set up at these farms to monitor the adult (moth) stages of European corn borer, corn earworm and fall armyworm, and we have begun scouting the fields for feeding injury by insect larvae. We will share the information we collected at these sites and management recommendations every week during the season through this newsletter and blog. If you would prefer to receive this newsletter via e-mail, give us a call at 207.933.2100 or send an e-mail message to:

A spell of warm, dry conditions in late April and early May allowed farmers to begin planting corn early through plastic mulch or under row covers. Some of this corn is now in the tassel stage, with a few fields showing some early silk. However, the more recent cool, damp conditions have kept development of later plantings very slow, varying from just a few leaves to early whorl stage. Both European corn borer and corn earworm moths are active in some fields, but their impact is limited if corn is not yet silking.

European corn borer:  We are just starting to find European corn borer moths in the pheromone traps around the state, and activity will likely increase over the next two weeks. These moths are now laying eggs on the undersides of corn leaves. The egg masses are small and look like overlapping fish scales. European corn borer is the only one of the three major insect pests of corn that can successfully overwinter in Maine, and it is usually the first pest to become a significant problem. To monitor corn borer, we scout 100 corn plants in each field, examining twenty plants in a row at five different locations. This sample provides a good estimate of the total amount of injury in a field. In the early stages, European corn borer feeding damage looks like small “pinholes” in the leaves. Corn in the whorl stage only needs to be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15%. This is because larvae feeding on the later stages are more likely to move into the ears of the plant. On the tassels, feeding damage first appears as chewing and brown waste found in the small florets. After the tassel has emerged from the stalk, the larvae chew into the stalk just below it, often causing the tassel to fall over. Sprays during the pre-tassel stage, when both moths and larvae are present, reduce the opportunity for larvae to move into the stalks and ears of the plant. Once the larvae are in the stalks they are protected from sprays.

Good spray coverage of the entire plant provides the most effective kill of larvae as they move from one part of the plant to another. Rotating the type of insecticide used also improves control. Materials registered for controlling European corn borer include Bacillus thuringiensis products (XenTari®, Dipel DF®), Avaunt®, Coragen®, Warrior®, Lannate®, Baythroid®, Asana®, Radiant®, Delta Gold®, Mustang®, Sevin XLR® and Larvin®. When corn reaches the silk stage, sprays may be based on the number of corn borer moths caught in pheromone traps rather than feeding injury. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught during a week in a field with silking corn, a spray will be recommended. Varieties of corn genetically modified to produce the Bt toxin (e.g. Bt corn, Attribute® varieties), should not need to be sprayed to control European corn borer. European corn borer feeding damage has been increasing in recent days and fields in No. Berwick, Sabattus and Livermore Falls were over the damage threshold in pre-tassel fields. Expect more injury to be showing up as more eggs begin to hatch. Early silking fields in Nobleboro and Warren were over the threshold for European corn borer moths caught in pheromone traps and sprays for those fields were recommended.

Corn earworm:  Pheromone traps are now set up around the state to monitor the arrival of corn earworm. Corn earworm generally appears in Maine in early July, but the actual date varies greatly. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths start being caught at a site, all silking corn in the fields should be protected with a spray. These moths lay eggs on the fresh silks and the larvae move directly into the ears of corn. When corn earworm moths cannot find silking corn to deposit their eggs on, they may lay eggs on the leaves of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm, until the ears become available. When larvae are found feeding on younger corn, the damage is accounted for, along with any borer or armyworm damage, to determine if a spray is warranted. We have caught a few corn earworm moths in a few southern and coastal locations this week. Only two fields are showing silk now and single moth catches do not warrant a spray.

Fall armyworm:  This is usually the last serious corn insect pest to arrive in Maine. The moths must fly in from southern over-wintering sites, and tend to lay their eggs on the youngest corn available. When the larvae hatch, they chew large, ragged holes in the leaves, and may bore into developing ears. Larvae may also move into the ears through the silk channel, behaving similarly to corn earworm. Pheromone trap catches will indicate if there is a threat to silking corn. However, corn will usually be on a spray program for corn earworm when fall armyworm is present, and both insects would be controlled.

Common stalk borer:  This pest can be a problem early in the season, but usually only around the edges of fields. The injury is similar to European corn borer, but the feeding holes are larger, with four or five holes running across the width of a leaf. The larvae are purple colored with white stripes. If high numbers of stalk borer are found in pre-tassel stage corn within the field (not just along the edges), include the injury with corn borer to determine if control is needed. Injury found in whorl stage corn is not a concern because the larvae will leave the plant before ears emerge.

Do-It-Yourself IPM:  To get the most accurate information about the pest situation on your farm you should monitor the fields yourself on a regular basis. Pheromone traps and lures are available that can give you an accurate, early warning of the arrival of all of the major insect pests. Traps and lures can be purchased from pest management supply companies such as Gempler’s (1.800.382.8473) or Great Lakes IPM (517.268.5693).

To learn more about IPM scouting techniques, insect identification and control thresholds, order the fact sheet Managing Insect Pests of Sweet Corn available from the University of Maine Cooperative Extension. Color pictures are provided to help with insect identification, and a chart with spray thresholds is supplied to post near your sprayer for easy reference. You can download a copy from the Pest Management website or call the Pest Management Office at 1.800.287.0279.

Hold the Date!
Highmoor Farm Field Day and Summer Tour is on Wednesday, July 31, 2013 from 9:00 a.m. to 3:00 p.m. Registration fee is $20.00, including lunch, and preregistration is strongly encouraged. For more information, visit the Highmoor Farm website. Please contact Pam St. Peter at or 207.933.2100 to preregister.


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                       Pest Management Office
P.O. Box 179                             491 College Avenue
Monmouth, ME  04259        Orono, ME  04473
207.933.2100                          1.800.287.0279

Sweet Corn IPM Weekly Scouting Summary

Location CEW
Recommendations / Comments
Auburn 1 25 No spray recommended (no silking corn)
Biddeford 0 5 0 10% No spray recommended (no silking corn)
Cape Elizabeth I 0 2 0 No spray recommended
Cape Elizabeth II 3 20 0 No spray recommended (no silking corn)
Dayton 1 0 0 0% No spray recommended (no silking corn)
Farmington 0 0 0 0% No spray recommended
Lewiston 0 0 0 0% No spray recommended
Livermore Falls 1 0 0 18% One spray recommended for ECB on pre-tassel corn
New Gloucester 0 1 0 0% No spray recommended
Nobleboro 0 26 0 2% One spray recommended for ECB on silking corn
No. Berwick 0 20 0 34% One spray recommended for ECB on pre-tassel corn
Oxford 0 4 0 No spray recommended (no silking corn)
Sabattus 0 33 0 19% One spray recommended for ECB on pre-tassel corn
Wales 0 0 0 0% No spray recommended
Warren 1 7 0 5% One spray recommended for ECB on silking corn
Wells I 0 2 0 0% No spray recommended
Wells II 0 0 0 0% 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:

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.

Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the State of Maine and the U.S. Department of Agriculture cooperating.  Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.

Image Description: Print Friendly

Image Description: Sweet Corn

Image Description: David Handley Checking Harstack Trap for Corn Earworm Moth

Image Description: European Corn Borer Moth

Image Description: European Corn Borer Damage on Pre-tassel Stage corn

Image Description: Corn Earworm Moth

Image Description: Fall Armyworm Moths

Image Description: Common Stalk Borer Damage

Image Description: High Tunnel Tomatoes


University of Maine Cooperative Extension

Contact Information

Cooperative Extension at Highmoor Farm
52 U.S. Route 202
Monmouth, Maine 04259-0179
Phone: 207.933.2100
The University of Maine
Orono, Maine 04469
A Member of the University of Maine System