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Sweet Corn IPM Newsletter No. 1 – June 26, 2015

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Sweet CornSweet Corn IPM Newsletter No. 1 – June 26, 2015
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European Corn Borer and Corn Earworm Moths Active in Early Fields

The 2015 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 are scouting the fields for feeding injury by insect larvae. We will share the information we collect at these sites along with 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:

Corn Field at Whorl Stage

Corn Field at Whorl Stage, photo by David Handley

A dry early spring and warm temperatures in May allowed farmers to get some early cornfields planted and growing. Cooler temperatures this month have slowed development of young plants, but overall growth looks good. Some very early corn, started under plastic or row covers is already beginning to silk in southern Maine. Most early fields are at late whorl and early pre-tassel. Some weather fronts coming up from the south have apparently brought some corn earworm in the state, and European corn borer moths are already active in some fields. Growers with early corn should be on the lookout for feeding damage in their fields.

European corn borer: Moths have been found in many of our pheromone traps this week, suggesting that this insect is off to an early start and is now laying eggs in young cornfields. The egg masses are small and look like a clump of overlapping fish scales on the undersides of corn leaves. European corn borer overwinters in Maine, and 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 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. Whorl stage corn 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% because larvae feeding on the later stages are more likely to move into the ears. 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®.

Thus far, we have only found corn borer feeding injury in a pre-tassel field in North Berwick. But the presence of moths in other locations suggests that feeding injury will soon become more widespread. Growers should start scouting whorl stage corn for feeding injury now. Once 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. If more than five moths are caught during a week in a field with silking corn, a spray is recommended. One field in Dayton had early silking corn this week, and was over the spray threshold for moths in the pheromone traps. Fields in Lewiston, Nobleboro and Wayne were also over the control threshold, but there was no silking corn at those sites, so no spray was 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 Moth

European Corn Borer Moth, photo by David Handley

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Corn earworm: Moths were caught in pheromone traps at two coastal sites this week (Nobleboro and Warren). This is a relatively early arrival of corn earworm in Maine, but because most locations do not yet have silking corn, they pose very little threat at this time. 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.

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. We have not yet caught any fall armyworm moths in our pheromone traps.

Harstack Trap

Harstack Trap, photo by David Handley

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 (Tel. 1.800.382.8473) or Great Lakes IPM (Tel. 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 Cooperative Extension Publications website at or call the Pest Management Office at 1.800.287.0279.

Hold the Date!
Highmoor Farm Field Day will be held on Wednesday, July 22, 2015. Visit the Highmoor Farm Field Day blog for more information.


David T. Handley
Vegetable and 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 /
Auburn 0 4 0 0% No spray recommended
Biddeford 0 0% No spray recommended
Bowdoinham 0 0 0 No spray recommended
Cape Elizabeth I 0 2 0 0% No spray recommended
Cape Elizabeth II 0 0 0 0% No spray recommended
Dayton I 0 8 0 0% One spray recommended for ECB on silking corn
Dayton II 0 0 0 0% No spray recommended
Farmington 0 3 0 0% No spray recommended
Lewiston 0 8 0 0% No spray recommended (no silking corn)
New Gloucester 0 0 0 0% No spray recommended
Nobleboro 3 41 0 0% No spray recommended (no silking corn)
No. Berwick 0 4 0 38% One spray recommended for ECB on pre-tassel corn
Oxford 0 0 0 0% No spray recommended
Poland Spring 0 0 0 0% No spray recommended
Sabattus 0 1 0 0% No spray recommended
Wales 0 0 0 0% No spray recommended
Warren 1 0 0 0% No spray recommended (no silking corn)
Wayne 0 5 0 0% No spray recommended (no silking corn)
Wells I 0 0 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.

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