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Sweet Corn IPM Newsletter No. 4 – July 6, 2012

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Sweet Corn

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


All Pests in Low Numbers, but Most Silking Corn Needs Protection

Some fields have been hit hard by thunderstorms during the past week while others saw only moderate temperatures and little, if any rain.  The later plantings are looking better than early seeded fields with better uniformity and growth.  Pests have been relatively quiet.  Although we have started to catch a few fall armyworm moths in our traps, we have not yet found any larvae feeding on corn.

European corn borer:  Moth counts were pretty low this week, although several sites were over the threshold of 5 moths in silking corn.  We did find more feeding injury from larvae in whorl and pre-tassel stage corn, with fields scouted in Biddeford, Lewiston, Sabattus and Wells over the recommended spray thresholds.

European Corn Borer Larva

European Corn Borer Larva, photo by David Handley

European Corn Borer Holes

European Corn Borer Holes, photo by David Handley

Corn earworm:  Moth counts remained low this week, and many fields do not have corn in silk, so the moths do not yet pose a significant threat to those fields.  A 6-day spray interval was recommended for silking fields in Cape Elizabeth, Dayton, Dresden, and New Gloucester.

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Fall armyworm:  We captured our first fall armyworm moths of the season this week in two southern Maine fields.  However, at these low levels, fall armyworm is not yet a threat.  Fall armyworm moths tend to lay their eggs on the youngest corn available.  When the larvae hatch, they chew large, ragged holes in the leaves, and may bore into developing ears.  This damage is scouted for along with European corn borer injury, and a spray is recommended if the injury exceeds 15% of plants in a pre-silking field.  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.

Male Fall Armyworm Moth

Male Fall Armyworm Moth, photo by David Handley

Late blight alert for potatoes and tomatoes

Late blight has recently been reported in tomato and potato plantings in coastal and central Maine.  Growers should be on the alert to catch any early symptoms and be ready to apply appropriate control measures.  Typical symptoms will be water-soaked lesions on the leaves with fine, white cottony mycelium on the undersides.  Infections on the stems appear as dark, almost black lesions.

Late Blight on Tomato

Late Blight on Tomato, photo by James Dill

Please report any suspicious symptoms to the Pest Management Office 581.3883 (1.800.287.0279), or email  The latest control options for late blight on tomatoes are on the University of New Hampshire Extension web site .


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 Moths FAW Moths % ECB Damage Recommendations / Comments
Biddeford  0  5  0  46% 1 spray recommended for ECB feeding (no silking corn)
Cape Elizabeth I  0  1  1  1% No spray recommended
Cape Elizabeth II  2  0  0  0% 6-day spray interval recommended for all silking corn
Charleston  0  0  0  0% No spray recommended
Dayton I  2  1  0  7% 6-day spray interval recommended for all silking corn
Dayton II  3  0  1  6% 6-day spray interval recommended for all silking corn
Dresden  3  2  0  8% 6-day spray interval recommended for all silking corn
East Corinth  0  0  0  1% No spray recommended
Farmington  0  0  0  3% No spray recommended
Jefferson  0  0  0  0% No spray recommended
Levant  0  2  0  0% No spray recommended
Lewiston  4  1  0  30% One spray recommended for ECB feeding (no silking corn)
Lewiston II  1  0  0  2% No spray recommended (no silking corn)
LivermoreFalls  0  2  0  0% No spray recommended
Monmouth  0  0  0  0% No spray recommended
New Gloucester  3  0  0  0% 6-day spray interval recommended for all silking corn
Nobleboro  0  1  0  0% No spray recommended
North Berwick  1  7  0  9% No spray recommended
Oxford  0  0  0  0% No spray recommended
Palmyra  0  2  0  2% No spray recommended
Poland Spring  0  1  0  12% No spray recommended
Sabattus  0  5  0  15% One spray recommended for ECB feeding
Wales  0  0  0  0% No spray recommended
Warren  0  0  0  3% No spray recommended
Wells I  0  1  0  16% One spray recommended for ECB feeding
Wells II  1  0  0  1% 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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