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Sweet Corn IPM Newsletter No. 9 – August 8, 2012

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

CORN EARWORM PUTS MOST LOCATIONS ON SPRAY SCHEDULE

Fall Armyworm Pressure Slowly Increasing

SITUATION
Corn harvest is in full swing across most of the state after the warm weekend weather.  Insect pressure has increased, especially from corn earworm with many locations being placed on 4-day spray intervals.  ECB pressure has remained low with the exception of a few northern locations, and fall armyworm appears to be slightly on the rise, but hasn’t exceeded thresholds anywhere.  With the prospect of southerly thunderstorms throughout most of the next week, insect pressure is not expected to decrease.

European corn borer:  Moth counts were still high in a few northern locations this week, requiring protection of silking corn, though only one location wasn’t already protecting against corn earworm.  Counts remained low in most southern fields.  Biddeford, Charleston, Levant, Palmyra, Wells 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 all locations this week, not exceeding the 15% feeding injury threshold in any locations.

Corn earworm:  Continued pressure from corn earworm has resulted in spray recommendations at all but 3 locations.  A 4-day spray interval was recommended in Biddeford, Cape Elizabeth, Dayton, Dresden, Levant, one Lewiston location, New Gloucester, Nobleboro, North Berwick, Oxford, and Wells.  A 5-day spray interval was recommended for Jefferson, Lewiston, Monmouth, Palmyra, Poland Spring, Sabattus, and Warren.  A 6-day spray interval was recommended for fields in Charleston and Livermore Falls.  Fields in Farmington and Wales caught single moths, which does not warrant a spray.

Fall armyworm:  Moth captures of fall armyworm are increasing.  When scouting, a spray is recommended if feeding injury exceeds 15% of plants in a pre-silking field.  However, larvae may also move into the ears through the silk channel, behaving similarly to corn earworm.  Pheromone trap catches of 3 or more moths per week indicate a spray is needed to protect silking corn, unless it is already under a spray schedule for corn earworm.  Two fall armyworm moths were caught at each Cape Elizabeth location, both Dayton locations, and a single moth was caught at each Wells location this week.  This is below threshold for silking corn.  No feeding damage was found.

Other Pests of Note:
Corn smut is often observed in fields this time of year.  This fungus disease is easily recognized by the large galls which form in the ears, tassels, and on leaves.  The young galls are silvery-white in color.  When the galls mature they rupture into masses of powdery, black spores.  This fungus tends to infect plants with a prior injury, perhaps from cultivation or insect feeding.  Smut usually affects a few plants in a field and is not considered an economically significant problem.  There is no effective fungicide for corn smut.

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  36  11  0  2% 4-day spray interval for all silking corn
 Cape Elizabeth I  50  0  2  0% 4-day spray interval for all silking corn
 Cape Elizabeth II  20  1  2  0% 4-day spray interval for all silking corn
 Charleston  3  11  0  3% 6-day spray interval for all silking corn
 Dayton I  14  0  2  1% 4-day spray interval for all silking corn
 Dayton II  8  0  2  0% 4-day spray interval for all silking corn
 Dresden  9  0  0  2% 4-day spray interval for all silking corn
 East Corinth  0  6  0  0% One spray recommended for ECB on silking corn
 Farmington  1  1  0  2% No spray recommended
 Jefferson  7  1  0  4% 5-day spray interval for all silking corn
 Levant  11  13  0  10% 4-day spray interval for all silking corn
 Lewiston  4  0  0  0% 5-day spray interval for all silking corn
 Lewiston II  9  0  0  8% 4-day spray interval for all silking corn
 Livermore Falls  2  2  0  1% 6-day spray interval for all silking corn
 Monmouth  6  1  0  7% 5-day spray interval for all silking corn
 New Gloucester  26  0  0  1% 4-day spray interval for all silking corn
 Nobleboro  14  3  0  5% 4-day spray interval for all silking corn
 North Berwick  15  3  0  6% 4-day spray interval for all silking corn
 Oxford  10  0  0  4% 4-day spray interval for all silking corn
 Palmyra  4  5  0  6% 5-day spray interval for all silking corn
 Poland Spring  5  0  0  6% 5-day spray interval for all silking corn
 Sabattus  7  0  0  9% 5-day spray interval for all silking corn
 Wales  1  0  0  4% No spray recommended
 Warren  7  0  0  8% 5-day spray interval for all silking corn
 Wells I  40  0  1  7% 4-day spray interval for all silking corn
 Wells II  48  5  1  1% 4-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 Larvae on Pre-tassel Stage Corn

Image Description: Corn Earworm

Image Description: Fall Armyworm Eggs on Corn

Image Description: Smut 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