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Sweet Corn IPM Newsletter No. 7 – July 25, 2012

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Sweet Corn

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


Western Bean Cutworm Found in Maine Corn Fields

Early harvest is getting into full swing and corn quality is looking good, although ear size has been a bit small due to dry conditions in some areas.  Moth counts continue to be very low for this time of year, but nobody is complaining.

European corn borer:  Moth counts were very low in southern locations this week, but some northern sites continue to have enough moths flying to warrant protection of silking corn.  Three sites, Charleston, Levant and East Corinth were over the threshold of 5 moths in silking corn.  Feeding injury from larvae in whorl to tassel stage corn was also less prevalent this week, only exceeding the 15% feeding injury threshold in Biddeford, Jefferson, Poland Spring and Sabattus.

European Corn Borer in Tassel

European Corn Borer in Tassel, photo by David Handley

Corn earworm:  There was a slight increase in moth activity in a few locations this week.  A 6-day spray interval for fresh silking corn was recommended for fields in Nobleboro, North Berwick, Palmyra, and Poland Spring.  Three locations had only single moths, which don’t warrant a spray.  Most locations had no moths.

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Fall armyworm:  No fall armyworm moths were caught this week and no feeding damage was found in the field.

Western bean cutworm:  A new corn pest for Maine?
We set out pheromone traps for western bean cutworm in cornfields this spring, based on reports that this insect is becoming a problem in corn in the upper Midwest and mid-Atlantic regions.  We have caught a few moths in Wells, Cape Elizabeth and New Gloucester over the past couple weeks, and we’re now evaluating what level of risk these present.  The larvae of western bean cutworm will feed on corn plants and move into the ears either through the silk channel or through the husks.  Unlike corn earworm, they are not cannibalistic; so many larvae may be found in a single ear, feeding on the kernels.  The threshold for feeding injury on plants is 8%.  There isn’t an established threshold for moths laying eggs in silking corn yet, but plants that are already on a spray program for corn earworm should also be protected from western bean cutworm.

Spotted wing drosophila update:  We have found this “new” fruit fly in more locations and in higher numbers this week, threatening raspberries, blueberries and any other soft fruit that is available.   We have now caught this fly in traps in Limington, Sanford, New Gloucester, Mechanic Falls, Wales, Litchfield, Fayette, Thorndike, and Warren.  Growers should be on the alert and look for fruit flies on their fruit and symptoms of premature fruit decay.  At this point, keeping fields free of overripe fruit and weekly insecticide sprays appear to be keeping this pest in check.  However more frequent sprays may become necessary as pest populations increase.  There is a good fact sheet on management of spotted wing drosophila on the Penn State Extension website.

Male and Female Spotted Wing Drosophila Flies

Male (left) and Female (right) Spotted Wing Drosophila, photo by Griffin Dill. Actual size: 2-3 mm.


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                      PestManagement 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
Recommendations / Comments
 Biddeford  0  0  0  30% One spray recommended for ECB feeding
 Cape Elizabeth I  0  0  0  6% No spray recommended
 Cape Elizabeth II  0  0  0  10% No spray recommended
 Charleston  0  5  0  1% One spray recommended for ECB on silking corn
 Dayton I  0  0  0  0% No spray recommended
 Dayton II  1  0  0  0% No spray recommended
 Dresden  0  0  0  9% No spray recommended
 East Corinth  0  6  0  0% One spray recommended for ECB on silking corn
 Farmington  0  1  0  3% No spray recommended
 Jefferson  0  0  0  19% One spray recommended for ECB feeding
 Levant  0  5  0  5% One spray recommended for ECB on silking corn
 Lewiston  0  0  3% No spray recommended
 Lewiston II  0  0  0  13% No spray recommended
 Livermore Falls  1  0  0  1% No spray recommended
 Monmouth  0  1  0  0% No spray recommended
 New Gloucester  0  0  0  2% No spray recommended
 Nobleboro  2  0  0  0% 6-day spray interval for all silking corn
 North Berwick  2  0  0  0% 6-day spray interval for all silking corn
 Oxford  0  1  0  5% No spray recommended
 Palmyra  2  3  0  3% 6-day spray interval for all silking corn
 Poland Spring  2  0  0  21% 6-day spray interval for all silking corn
 Sabattus  0  0  0  23% One spray recommended for ECB feeding
 Wales  0  0  0  0% No spray recommended
 Warren  0  0  0  0% No spray recommended
 Wells I  1  0  0  0% No spray recommended
 Wells II  0  1  0  6% 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.

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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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