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Sweet Corn IPM Newsletter No. 3 – June 29, 2012

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Sweet Corn

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


Corn Earworm Threatens Fields in Southern Maine

Hard to believe, but most fields have again seen at least an inch of rain in the past week.  Early stands are very uneven due to the rain and cool temperatures, but we may see some corn ready to harvest in about two weeks.  Many fields also show symptoms of nitrogen and zinc deficiencies, as a result of all the rain and leaching of fertilizers.  We’re seeing apparent breakdown of herbicides as well, and growers may want to review the weed control information in the 2012-2013 New England Vegetable Management Guide to assess post-emergent herbicide options.

European corn borer:  Moth counts continue to be fairly low this week, although with the advent of silking corn in southern Maine we should pay close attention to these counts.  Moths may lay their eggs on the flag leaves of silking corn resulting in larvae entering the ears through the silk channels without leaving any visible signs of feeding on the foliage.  Therefore, if 5 or more European corn borer moths are caught in a trap over a week in the presence of silking corn, a spray to protect the silks is recommended.  We continue to find feeding injury from small larvae in whorl and pre-tassel stage corn, but only fields scouted in Biddeford and Warren were over the recommended spray threshold.  Corn in the whorl stage should be sprayed if fresh feeding injury is found on 30% or more of the plants in a field.  At the pre-tassel stage, the control threshold is lowered to 15%.

European Corn Borer Larvae on Pre-tassel Stage Corn

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

Corn earworm:  Moth counts were low this week, but we’re finding corn earworm in more locations.  Some fields do not yet have silking corn present, so the moths do not represent a significant threat at the moment.  A single spray was recommended for silking fields in Dayton and North Berwick where their first corn earworms were caught.  A 6-day spray interval was recommended for silking fields in New Gloucester, Sabattus, and another Dayton location.

Fall armyworm:  We have not yet caught any fall armyworm moths in our pheromone traps.  However, because most of our recent weather seems to be coming up from the south, we should expect the arrival of this insect, as well as a likely increase in corn earworm populations, in the near future.

Male Fall Armyworm Moth

Male Fall Armyworm Moth, photo by David Handley

Common armyworm:  Feeding damage from this pest has declined significantly since last week.  It is likely that larvae have started to leave the plants to pupate.

Aphids:  Be on the lookout for infestations of aphids developing on the tassels, silks and husks.  Aphid feeding is not usually a significant problem.  However, black sooty mold often develops on the husks as a result of the waste (called honeydew) aphids deposit, and can render the ears unmarketable.  Insecticide sprays, other than the Bt’s or spinosad products, that are used to control the major corn pests also offer control of aphids as well, including Asana®, Capture®, Warrior® and Lannate®.

Aphids on Corn Ear

Aphids on Corn Ear, photo by David Handley

Japanese beetles are becoming plentiful in southern and mid-state areas. These insects often find their way into corn fields and may feed on the silks of developing ears, causing poor tip fill.  Sprays for corn earworm (except Bt’s) will often control Japanese beetle as well.

Japanese Beetle

Japanese Beetle, photo by Edwin Remsberg, USDA


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                      PestManagement 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 1 0 31% 1 spray recommended for ECB feeding (no silking corn)
Cape Elizabeth I 0 0 0 0% No spray recommended
Cape Elizabeth II 0 2 0 1% No spray recommended
Dayton I 1 0 0 12% One spray recommended for all silking corn
Dayton II 2 0 0 0% 6-day spray interval recommended for all silking corn
Dresden 0 0 0 7% No spray recommended
Farmington 0 0 0 3% No spray recommended
Jefferson 0 3 0 1% No spray recommended
Lewiston 0 0 0 0% No spray recommended
Lewiston II 0 8 0 5% No spray recommended (no silking corn)
Livermore Falls 0 2 2 0% No spray recommended
New Gloucester 2 0 0 5% 6-day spray interval recommended for all silking corn
Nobleboro 0 4 0 0% No spray recommended
North Berwick 1 0 0 0% One spray recommended for all silking corn
Oxford 0 7 0 4% No spray recommended (no silking corn)
Poland Spring 1 0 1% No spray recommended
Sabattus 2 2 0 5% 6-day spray interval recommended for all silking corn
Wales 0 0 0 2% No spray recommended
Warren 0 2 0 18% One spray recommended for ECB feeding
Wells I 0 2 0 No spray recommended
Wells II 0 4 0 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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