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Sweet Corn IPM Newsletter No. 8 – August 1, 2012

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

CORN EARWORM PRESSURE INCREASES IN SOUTHERN MAINE

European Corn Borer and Fall Armyworm Threat Remains Small

SITUATION
Harvest is still spotty as growers work through the erratic early corn and hope for better uniformity and quality with the main season crop.  Many fields received just enough rain to get a break from irrigation this week.  A little bit of weather coming up from the southeast coast appears to have bumped up local corn earworm populations, so silking corn is likely to need protection, especially in the southern and coastal areas of the state.

European corn borer:  Moth counts were higher in some northern locations this week, requiring protection of silking corn, but remained low in most southern fields.  Charleston, Levant, Palmyra and East Corinth were over the threshold of 5 moths in silking corn.  Feeding injury from larvae in whorl to tassel stage corn remained low in most locations this week, only exceeding the 15% feeding injury threshold in Cape Elizabeth and Poland Spring.

Corn earworm:  A significant increase in moth activity over the past two nights has increased the number of fields needing to protect any fresh silking corn.  A 4-day spray interval was recommended in one Cape Elizabeth location and North Berwick.  A 5-day spray interval was recommended for Biddeford, a second Cape Elizabeth location, Monmouth and New Gloucester.  A 6-day spray interval was recommended for fields in Lewiston,Warren and Wells.  Fields in Dayton, Jefferson, Palmyra, Poland Spring and Sabattus caught single moths, which does not warrant a spray.

Fall armyworm:  Two fall armyworm moths were caught in one Cape Elizabeth location this week.  This is below threshold for silking corn.  No feeding damage was found.

Spotted wing drosophila update:  The numbers and range of the “Suzuki Fruit Fly” continue to increase around the state.  We have found this small fruit fly in traps in Limington, Buxton, Sanford, New Gloucester, Mechanic Falls, Poland Spring, Wales, Litchfield, Fayette, Thorndike, Warren and Bucksport.  This week also saw the first capture of this fly in a wild blueberry field in Franklin.  Berry growers need to be on the alert for fruit flies and symptoms of premature fruit decay.  Have your pickers keep fields free of overripe fruit.  At this point, insecticide sprays every 5-7 days appears to provide adequate control.  More frequent sprays may become necessary as populations increase.  There is a good fact sheet about the management of spotted wing drosophila on the Penn State Extension website.

Corn rust causes reddish-brown pustules to form on the leaves, stalks and husks, reducing the visual quality of the ears.  We see more of this problem in wet, humid seasons.  Some varieties are resistant.  Severe infections can reduce ear size, especially if they occur prior to tassel.  A fungicide spray for rust is only recommended if the infection occurs prior to tasseling.  Later infections are unlikely to cause enough damage to the crop to justify control measures.  Materials available to control corn rust include Bravo®, Quilt® and maneb/mancozeb.

Sincerely,

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  7  3  0  4% 5-day spray interval for all silking corn
 Cape Elizabeth I  11  0  2  0% 4-day spray interval for all silking corn
 Cape Elizabeth II  6  0  0  21% 5-day spray interval for all silking corn
 Charleston  0  9  0  1% One spray recommended for ECB on silking corn
 Dayton I  1  1  0  3% No spray recommended
 Dayton II  1  0  0  1% No spray recommended
 Dresden  0  1  0  5% No spray recommended
 East Corinth  0  20  0  0% One spray recommended for ECB on silking corn
 Farmington  0  0  0  2% No spray recommended
 Jefferson  1  0  0  7% No spray recommended
 Levant  0  8  0  6% One spray recommended for ECB on silking corn
 Lewiston  2  1  0  0% 6-day spray interval for all silking corn
 Lewiston II  2  3  0  9% 6-day spray interval for all silking corn
 Monmouth  6  2  0  7% 5-day spray interval for all silking corn
 New Gloucester  5  0  0  2% 5-day spray interval for all silking corn
 North Berwick  8  0  0  1% 4-day spray interval for all silking corn
 Oxford  0  0  0  8% No spray recommended
 Palmyra  1  6  0  5% One spray recommended for ECB feeding
 Poland Spring  1  3  0  30% One spray recommended for ECB feeding
 Sabattus  1  1  0  8% No spray recommended
 Wales  0  0  0  13% No spray recommended
 Warren  3  0  0  7% 6-day spray interval for all silking corn
 Wells I  3  0  0  0% 6-day spray interval for all silking corn
 Wells II  3  0  0  1% 6-day spray interval for all 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:
http://extension.umaine.edu/ipm/
http://www.pestwatch.psu.edu/sweet_corn.htm
http://www.umass.edu/umext/ipm/

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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Image Description: Sweet Corn

Image Description: European Corn Borer Moth

Image Description: Corn Earworm Moth

Image Description: Male Spotted Wing Drosophila

Image Description: Male and Female Spotted Wing Drosophila

Image Description: Rust on Corn


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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
207.581.1110
A Member of the University of Maine System