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Sweet Corn IPM Newsletter No. 6 – July 19, 2012

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Sweet Corn

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


Spotted Wing Drosophila Alert

Despite the warmer night temperatures over the weekend, moth counts remain low.  In many places, the warm nights helped the corn grow rapidly, while in other places corn is exhibiting symptoms of dehydration because of the lack of rain.

European corn borer:  Moth counts continue to be very low this week.  Two sites, Levant and East Corinth were over the threshold of 5 moths in silking corn.  Feeding injury from larvae in whorl to tassel stage corn exceeded the 15% feeding injury threshold in Biddeford, one Cape Elizabeth location, Jefferson, one Lewiston location, Oxford, Poland Spring, Sabattus and one Wells location this week.


European Corn Borer on Ear

European Corn Borer on Ear, photo by David Handley

Corn earworm:  No sprays were recommended for corn earworm this week.  Most locations had no moths, and the locations where corn earworm was present only saw a single moth, which doesn’t warrant a spray.

Fall armyworm:  Though we were expecting moth counts to increase after the warmer nights over the weekend, no fall armyworm moths were caught this week and we have not yet seen any sign of larvae feeding.

Spotted Wing Drosophila (SWD) Alert:  This is a new pest which is a concern for raspberries, blueberries, and day-neutral strawberries, as well as many other soft fruits.  This insect is a small fruit fly, similar to the type that fly around the over-ripe bananas in your kitchen.  However, this species will lay its eggs in fruit before it ripens, resulting in fruit that is contaminated with small white maggots just as it is ready to pick.  As a result, the fruit quickly rots and has no shelf life.  This insect recently came into the U.S. from northern Asia, and caused problems with many berry crops up the east coast last year.  It can complete a generation in under two weeks, with each adult female laying hundreds of eggs.  Therefore, millions of flies can be present soon after the introduction of  just a few into a field.  This makes them very difficult to control, and frequently repeated insecticide sprays (3 to 5 times per week) may be needed to prevent infestations once the insect is present in a field.  Now that spotted wing drosophila has been confirmed in Limington, Mechanic Falls, Springvale, Thorndike, and Warren, growers should be on the alert and look for fruit flies on their fruit and symptoms of premature fruit decay.  Products that provide good control of drosophila on berries include Delegate®, Brigade®, Danitol®, and malathion.  Please check product labels for rates, post-harvest intervals and safety precautions. Keeping the fields clean of over-ripe and rotten fruit can also help reduce the incidence of this insect. For information on identifying spotted wing drosophila and making your own monitoring traps, visit the Michigan State University’s Spotted Wing Drosophila.  There is also a good fact sheet on management of spotted wing drosophila on the Penn State Extension website.

Male and Female Spotted Wing Drosophila Flies


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
%ECB Damage Recommendations / Comments
 Biddeford  1  0  0  24% One spray recommended for ECB feeding
 Cape Elizabeth I  0  1  0  1% No spray recommended
 Cape Elizabeth II  0  0  0  29% One spray recommended for ECB feeding
 Charleston  0  1  0  0% No spray recommended
 Dayton I  1  0  0  0% No spray recommended
 Dayton II  1  1  0  0% No spray recommended
 Dresden  0  0  0  3% No spray recommended
 East Corinth  0  6  0  2% One spray recommended for ECB on silking corn
 Farmington  1  0  0  6% No spray recommended
 Jefferson  1  1  0  25% One spray recommended for ECB feeding
 Levant  0  5  0  5% One spray recommended for ECB on silking corn
 Lewiston  1  1  0  2% No spray recommended
 Lewiston II  0  2  0  13% No spray recommended
 Livermore Falls  0  0  0  2% No spray recommended
 Monmouth  0  0  0  0% No spray recommended
 New Gloucester  0  0  0  1% No spray recommended
 Nobleboro  0  4  0  4% No spray recommended
 North Berwick  0  0  0  4% No spray recommended
 Oxford  0  0  0  27% One spray recommended for ECB feeding
 Palmyra  0  3  0  1% No spray recommended
 Poland Spring  1  0  0  41% One spray recommended for ECB feeding
 Sabattus  0  0  0  19% One spray recommended for ECB feeding
 Wales  0  0  0  0% No spray recommended
 Warren  0  0  0  7% No spray recommended
 Wells I  1  1  0  18% One spray recommended for ECB feeding
 Wells II  0  0  0  2% 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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