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Sweet Corn IPM Newsletter No. 2 – June 22, 2012

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Sweet Corn

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


European Corn Borer and Common Armyworm Feeding in Southern Maine

The recent hot spell has pushed corn growth along rapidly, and brought us our first corn earworm of the season.  Many early fields are approaching the pre-tassel stage, and should be getting a side dressing of nitrogen, if needed.  Some corn started under plastic in southern Maine is now tasseling and showing some silk.  Soil moisture levels remain pretty good in most locations due to the over abundance of rain earlier.

European corn borer:  We caught just a few European corn borer moths in southern Maine this week, in spite of the warmer temperatures that usually stimulate moth activity.  Corn borer moths are now laying eggs on corn leaves, and we have started finding small larvae feeding in the whorls.  At this time, the feeding damage looks like 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 (30 out of 100 plants sampled).  Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15%.  Pre-tassel fields in Poland Spring and New Gloucester were over the spray threshold for damage this week, and we expect to find more injury soon as more eggs begin to hatch.

European Corn Borer Trap

European Corn Borer Trap, photo by David Handley

European Corn Borer Moth

European Corn Borer Moth, photo by David Handley

Corn earworm:  We caught our first corn earworm of the 2012 season in New Gloucester this week.  No moths have been found yet in other locations.New Hampshire has not yet reported any moths, but a few have been caught in Massachusetts.  Corn earworm is only a concern for fields with silking corn.  A spray is recommended to protect silking corn when corn earworm is first detected in a field.  Additional spray recommendations are based on the average number of moths caught in traps per night or per week.  This week, a six-day spray interval is recommended for all silking corn in the New Gloucester field.

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Fall armyworm:  No fall army worm moths have been caught in our pheromone traps this week. New Hampshire and Massachusetts have not yet reported any fall armyworm in their fields.

Common armyworm:  One field in southern Maine was found with over 30% damage from common armyworm larvae this week.  These caterpillars chew large holes in young corn early in the season.  The larvae are light brown with yellow and black stripes running along the body.  With light infestations, the corn may outgrow the injury.  However, when heavy infestations occur, control may be required.

Common Army Worm

Common Army Worm, photo by Purdue University

Brown marmorated stink bug is a “new” pest from Asia that caused significant damage to sweet corn in southern and Mid-Atlantic states last year.  Although this insect looks similar to our native brown stink bug, it can colonize cornfields in great numbers, piercing the husks and sucking the juices out of the kernels, causing considerable damage.  This species can be distinguished from brown stink bug by small white stripes on the antennae and legs, and by its aggregating behavior.  Several insecticides registered for sweet corn appear to offer good control of this stink bug, if it appears on corn in Maine, including Baythroid® and Lannate®.  Companies are working to get products specifically registered for brown marmorated stink bug on corn and other crops to deal with this new problem.

brown marmorated stink bug


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                      Pest Management Office
P.O. Box179                          491 College Ave
Monmouth,ME 04259            Orono,ME 04473
207.933.2100                        1.800.287.0279


Sweet Corn IPM Weekly Scouting Summary

Location CEW Moths ECB Moths FAW Moths % ECB Damage Recommendations / Comments
Biddeford 0 0 0 0% No spray recommended
Cape Elizabeth I 0 0 0 0% No spray recommended
Cape Elizabeth II 0 1 0 0% No spray recommended
Dayton I 0 0 0 0% No spray recommended
Dayton II 0 0 0 0% 32% common armyworm damage, spray recommended
Dresden 0 0 0 0% No spray recommended
Farmington 0 0 0 1% No spray recommended
Jefferson 0 0 0 0% No spray recommended
Lewiston I 0 0 0 0% No spray recommended
Lewiston II 0 0 0 5% No spray recommended
Livermore Falls 0 0 0 0% No spray recommended
New Gloucester 3 6 0 24% 6-day spray interval recommended for all silking corn
Nobleboro 0 0 0 3% No spray recommended
North Berwick 0 0 0 0% No spray recommended
Oxford 0 0 0 0% No spray recommended
Poland Spring 0 4 0 54% One spray recommended for ECB feeding
Sabattus 0 0 0 0% No spray recommended
Warren 0 0 0 3% No spray recommended
Wells I 0 1 0 0% No spray recommended
Wells II 0 8 0 0% No spray recommended (no 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:

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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