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Sweet Corn IPM Newsletter No. 2 – June 29, 2011

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Sweet Corn

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EARLY CORN EARWORM A CONCERN FOR EARLY SILKING CORN

European Corn Borer Activity Increasing

SITUATION
Good growing conditions for corn have been limited this week as night time temperatures continue to be cool.  In spite of recent showers, some fields are quite dry, which may be further slowing development.  While most early fields in southern Maine are now at pre-tassel, many are still in the whorl stage.  A few plantings started under mulch or row covers are now silking.  Two out of three of the major pests are already active, which means it is unlikely that early corn will escape significant pest pressure this year.

European corn borer:  Moth numbers were variable this week from farm to farm, ranging from no moths up to 49 at one site.  Most farms are seeing some moth activity, however, suggesting that larval feeding pressure is likely to increase in the near future.  Several farms exceeded the threshold of five or more moths for silking corn, but only two of these locations had silking corn and one of those had already been put on a spray schedule for corn earworm.  We are now finding the typical small “pinholes” in the leaves of whorl and pre-tassel stage corn plants.  Corn in the whorl stage only needs to be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field.  Corn at the pre-tassel stage should be sprayed if 15% or more of plants are showing injury.  Sprays during the pre-tassel stage when both moths and larvae are present can stop larvae from moving into the stalks and ears of the plant.  This week, fields in Dry Mills (Poland Spring area) and Nobleboro were found to be over threshold for European corn borer feeding injury.  We expect feeding injury to become more widespread as the eggs now being laid in the fields begin to hatch.

European Corn Borer Holes

European Corn Borer Holes, photo by David Handley

 

European Corn Borer Larvae on Pre-tassel Stage Corn

European Corn Borer Larvae on Pre-tassel Stage Corn, photo by David Handley

 

Corn earworm:  Pheromone trap catches this week indicate the corn earworm has become fairly widespread in southern and coastal Maine areas.  Although moth counts are still relatively low, numbers have been high enough to recommend sprays for some fields with early silking corn.  The frequency of sprays required to protect silking corn increases as the number of moths caught per week increases as shown in the table below.  Remember that fields not yet in silk do not need to be protected from corn earworm.  This week a six-day spray schedule for silking corn was recommended for silking corn fields in Dayton.  Moth captures also occurred in Biddeford, Cape Elizabeth, Lewiston, Livermore, New Gloucester, Readfield, Sabattus and Wells; but fields at these sites were either not yet in silk, or the moth counts were not high enough to warrant a spray.

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

 

Green Silk Stage

Green Silk Stage, photo by David Handley

 

Fall armyworm:  In spite of our first moth being caught in a trap in Levant last week, no further captures of fall armyworm have occurred this week.  This is typically the last serious corn insect pest to arrive here, usually in mid-July; but given the early arrival of corn earworm, more  catches in the coming days would not be a great surprise.

Male Fall Armyworm Moth

Male Fall Armyworm Moth, photo by David Handley

 

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                       Pest Management Office
P.O. Box 179                          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 3 0 0 12% No spray recommended (no silking corn)
Cape Elizabeth I 1 7 0 No spray recommended (no silking corn)
Cape Elizabeth II 5 2 0 1% No spray recommended (no silking corn)
Corinth I 0 0 0 0% No spray recommended
Corinth II 0 0 0 0% No spray recommended
Dayton I 3 3 0 0% 6 day spray interval recommended for all silking corn
Dayton II 3 15 0 1% 6-day spray interval recommended for all silking corn
Dresden 0 12 2% No spray recommended (no silking corn)
Farmington 0 2 0 0% No spray recommended
Jefferson 0 1 0 0% No spray recommended
Levant 0 0 0 0% No spray recommended
Lewiston I 0 0 0 3% No spray recommended
Lewiston II 7 4 0% No spray recommended (no silking corn)
Livermore 1 2 0 8% No spray recommended
New Gloucester 1 2 0 0% No spray recommended
North Berwick 0 13 0 No spray recommended
Oxford 0 2 0 6% No spray recommended
Palmyra 0 0 0 0% No spray recommended
Poland Spring 0 4 0 43% One spray recommended for ECB
Nobleboro 0 12 21% One spray recommended for ECB
Readfield 1 5 0 1% No spray recommended (no silking corn)
Sabattus 1 49 9% No spray recommended (no silking corn)
Wales 0 0 0% No spray recommended
Warren 0 4 1% No spray recommended
Wells I 0 0 0 1% No spray recommended
Wells II 4 10 0 2% No spray recommended (no 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.

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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