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Sweet Corn IPM Newsletter No. 5 – July 11, 2012

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Sweet Corn

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


First Corn Harvested in Southern Maine this Week

A stretch of warm, dry weather has corn plantings growing well, although cool nights have prevented rapid growth, and appears to have kept moth activity low.  Some very early corn started under row covers was harvested in southern Maine this week, while early fields further north are just coming into silk.

Corn in Silk Stage

Corn in Silk Stage, photo by David Handley

European corn borer:  Moth counts continue to be very low this week.  Two sites, Sabattus 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, Jefferson, one Lewiston location, Poland Spring, Sabattus and Warren this week.  Many of the larvae are quite large, suggesting that they may be pupating before ear development in later fields, but some smaller larvae are also present, which could move into silking corn as it becomes available.

European Corn Borer in Tassel

European Corn Borer in Tassel, photo by David Handley

Corn earworm:  With few exceptions, moth counts have been very low this week.  A 5-day spray interval on any silking corn was recommended in Nobleboro where four moths were caught this week, and a 6-day spray interval was recommended for silking fields in Dresden. In fields that do not yet have silking corn, earworm is not a threat.

Fall armyworm:  Despite our first fall armyworm captures last week, we caught no moths this week, and have not yet seen any sign of larvae feeding.  When warmer nights prevail, we can expect the moths to become more active and the larvae to threaten all growth stages of corn.

Potato leafhopper alert:  Symptoms of potato leafhopper feeding are becoming apparent in vegetable and strawberry fields this week.  Leafhoppers are small, bullet-shaped insects that feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked.  Beans are quite susceptible to the injury, in addition to potatoes and strawberries.  To scout for leafhoppers, brush the leaves of the plants with your hand.  The small, whitish adults can be seen flying off the plant.  Look for small, light green leafhopper nymphs on the underside of injured leaves.  They are about 1/16 inch long.  When touched, they crawl sideways in a crab-like manner.  Controls for potato leafhoppers are listed in the New England Vegetable Management Guide.

Potato Leafhopper - Adult & Nymph

Potato Leafhopper – Adult and Nymph, photo by Penn State College of Agricultural Sciences

Squash vine borer moths are being caught in pheromone traps in southern Maine.  The moths lay their eggs at the base of squash or pumpkin plants, and the larvae tunnel into the vines, causing them to wilt and collapse.  Entry holes can often be found near the base of the plant.  Sprays can be applied to control the moths and prevent egg-laying.  Plow down squash plantings as soon as harvest is complete to prevent borers from overwintering in the field.  There is one generation per year.  See the New England Vegetable Management Guide for more details. 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  1  2  0  69% 1 spray recommended for ECB feeding (no silking corn)
CapeElizabeth I  0  0  0  0% No spray recommended
CapeElizabeth II  0  0  0  4% No spray recommended
Charleston  0  1  0  1% No spray recommended
Dayton I  1  1  0  0% No spray recommended
Dayton II  1  0  0  8% No spray recommended
Dresden  3  2  0  8% 6-day spray interval recommended for all silking corn
East Corinth  0  6  0  0% One spray recommended for ECB on silking corn
Farmington  0  0  0  3% No spray recommended
Jefferson  0  0  0  20% One spray recommended for ECB feeding
Levant  0  0  0  0% No spray recommended
Lewiston  1  0  0  2% No spray recommended
Lewiston II  4  1  0  30% 1 spray recommended for ECB feeding (no silking corn)
Livermore Falls  0  0  0  0% No spray recommended
Monmouth  0  0  0  0% No spray recommended
NewGloucester  0  0  0  1% No spray recommended
Nobleboro  4  0  0  5% 5-day spray interval recommended for all silking corn
North Berwick  0  0  0  13% No spray recommended
Oxford  0  0  0  9% No spray recommended
Palmyra  0  0  0  0% No spray recommended
Poland Spring  2  1  0  44% 6-day spray interval recommended for all silking corn
Sabattus  0  5  0  15% One spray recommended for ECB on silking corn
Wales  0  0  0  0% No spray recommended
Warren  0  0  0  16% One spray recommended for ECB feeding
Wells I  0  1  0  7% No spray recommended
Wells II  0  1  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.

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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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