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Sweet Corn IPM Newsletter No. 3 – July 7, 2011

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Sweet Corn

For full page print version, please see link at the bottom.

CORN EARWORM INCREASING THREAT TO EARLY CORN

Warm Weather Pushes Early Corn into Silk

SITUATION
Early corn planted under plastic mulch or row covers is now in the silk stage in southern Maine, while uncovered early fields are in the pre-tassel to tassel stage.  Many late-planted fields are still in the whorl stage, but warm weather and plenty of soil moisture should move things along quickly.  Corn earworm moths threaten early silk in most locations.

Green Silk Stage

Green Silk Stage, photo by David Handley

 

European corn borer:  Moth numbers decreased in most locations this week and damage increased.  Moths were over the 5 moth threshold in North Berwick, Oxford, Nobleboro, Sabattus, Warren and one Wells site.  Sprays for silking corn were only recommended in North Berwick, Sabattus and Wells; other sites either had no silking corn or were already on a spray schedule for corn earworm.  ECB field damage exceeded threshold in whorl stage corn (30%) in Poland Spring, and a spray was recommended.  Field damage was over threshold in pre-tassel stage corn (15%) in North Berwick, Oxford, and Sabattus, therefore sprays were recommended for these sites as well.

European Corn Borer Damage

European Corn Borer Damage, photo by David Handley

 

European Corn Borer Larvae on Pre-tassel Stage Corn

 

Corn earworm:  Corn earworm trap counts remain low, but with more silking corn they are becoming more of a threat.  A few more sites are on spray schedules this week.  A six-day spray schedule for silking corn was recommended for silking corn fields in Jefferson.  Five-day spray schedules for silking corn were recommended in Dayton and Livermore.  A four-day spray interval was recommended in Nobleboro.  Moth captures also occurred in Biddeford, Cape Elizabeth, Dresden, Farmington, Lewiston, New Gloucester, North Berwick, Oxford, Poland Spring, Warren 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

 

Fall armyworm:  Fall armyworm is still not a threat this week. This week one single moth was caught in a trap in New Gloucester. For silking corn 3 or more moths must be caught for a spray to be recommended.  Armyworm moths prefer to lay their eggs on young corn plants.  When found, this injury is combined with any European corn borer injury to determine if protection is needed.  Control thresholds are 30% infestation in whorl stage corn or 15% for corn at pre-tassel and beyond.

Late Blight:  Grower and Farm Stand Alert
Late blight has recently been reported in tomato and potato plantings in Long Island, New York, and fields in Delaware and Virginia.  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.  For more photos of the symptoms, visit Cornell University Extension’s web pages for late blight on tomato and late blight on potato.

Potato Plant Infected with Late Blight

Potato Plant Infected with Late Blight, photo by Dr. Steven Johnson

 

Late Blight on Tomato Leaves

Late Blight on Tomato Leaves, photo by Dr. Steven Johnson

 

Late blight spores can travel over 40 miles under the right conditions (wet and warm) and the spread can be very fast.  We are encouraging all growers to carefully and regularly inspect their plants for this disease.  Please report any suspicious symptoms to the Pest Management Office at 581.3883 (1.800.287.0279 in-state), or email PMO@umext.maine.edu.  Samples can be sent to:

Pest Management Office
491 College Avenue
Orono, ME  04473-0279

Samples should be sent in a plastic bag with a dry paper towel to keep them fresh.

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 4 1 0 10% No spray recommended (no silking corn)
Cape Elizabeth I 3 3 0 2% No spray recommended (no silking corn)
Cape Elizabeth II 13 4 0 1% No spray recommended (no silking corn)
Corinth I 0 1 0 0% No spray recommended
Corinth II 0 0 0 0% No spray recommended
Dayton I 6 4 0 7% 5 day spray interval recommended for all silking corn
Dayton II 4 0 0 14% 5 day spray interval recommended for all silking corn
Dresden 1 3 0 5% No spray recommended
Farmington 1 0 0 2% No spray recommended
Jefferson 2 1 0 0% 6 day spray interval recommended for all silking corn
Levant 0 2 0 0% No spray recommended
Lewiston I 1 2 0 2% No spray recommended
Lewiston II 11 3 0 0% No spray recommended (no silking corn)
Livermore 4 1 0 8% 5 day spray interval recommended for all silking corn
New Gloucester 1 2 1 1% No spray recommended
North Berwick 1 5 0 16% One spray recommended for ECB (pre-tassel – silk)
Oxford 2 5 0 15% One spray recommended for ECB (pre-tassel)
Palmyra 0 2 0 6% No spray recommended
Poland Spring 1 0 0 61% One spray recommended for ECB (whorl)
Nobleboro 8 22 0 13% 4 day spray interval recommended for all silking corn
Readfield 0 2 0 2% No spray recommended
Sabattus 0 18 0 34% One spray recommended for ECB (pre-tassel – silk)
Wales 0 1 0 1% No spray recommended
Warren 1 11 0 3% No spray recommended (no silking corn)
Wells I 1 0 0 12% No spray recommended
Wells II 1 6 0 5% One spray recommended on all silking corn for ECB

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.

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.

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