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Sweet Corn IPM Newsletter No. 2 – July 8, 2013

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Sweet Corn

Sweet Corn IPM Newsletter No. 2 – July 8, 2013

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


Silking Corn Needs Protection in Early Fields

Warm conditions and lots more rain have kept corn growing, but made it difficult to do any field work, such as spraying or side-dressing. Early fields in some areas are showing silk, and later fields, although uneven, are coming into pre-tassel. Some growers have had difficulty getting onto wet ground to seed their last plantings. The rain also is raising concerns about fertilizer and herbicide leaching.

European corn borer:  Moth catches were irregular this week with about half of the sites having any moths caught, and just a few over threshold for early fields with silking corn. Activity may increase over the next week, as the wet weather might extend the emergence of this first generation of moths. European corn borer feeding damage was over threshold in pre-tassel fields in Biddeford, Cape Elizabeth, Livermore Falls, and Nobleboro this week. One field (No. Berwick) that had both silking corn and was over threshold for moths was also put on a spray program for corn earworm, so no additional sprays were required.

European Corn Borer Damage

European Corn Borer Damage, photo by David Handley

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Corn earworm:  About one half of the fields visited this week had corn earworm moths in pheromone traps. Most of these fields do not yet have any silking corn, so no sprays were recommended. When more than one corn earworm moth is found at a site, all silking corn in the fields should be protected with a spray. Additional sprays are based on the average number of moths caught per week or per night (see table below). Silking fields in Dayton, No. Berwick and Wells were recommended to go on a 6-day spray program for silking corn this week, based on a weekly capture of 3 moths.

Male Fall Armyworm Moth

Male Fall Armyworm Moth, photo by David Handley

Fall armyworm:  We have caught a couple of fall armyworm moths in pheromone traps this week, although the identification has not been confirmed. We have not yet seen any feeding damage from this pest, so no sprays for fall armyworm have been recommended.

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.

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

Male and Female Spotted Wing Drosophila Flies

Male (left) and Female (right) Spotted Wing Drosophila, photo by Griffin Dill. Actual size: 2-3 mm.

Spotted wing drosophila:  We have had our first captures of spotted wing drosophila in New Hampshire and Maine this week. These small fruit flies can cause serious fruit losses in raspberries, blueberries and other soft fruits. The flies will only attack fruit that has begun to ripen, and we don’t expect populations to reach damaging levels for a few weeks. For more information visit the Highmoor Farm website.


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                       Pest Management Office
P.O. Box 179                             491 College Avenue
Monmouth, ME  04259        Orono, ME  04473
207.933.2100                          1.800.287.0279

Sweet Corn IPM Weekly Scouting Summary

Location CEW
Recommendations / Comments
Auburn 0 7 0 8% No spray recommended (no silking corn)
Biddeford 0 2 0 42% One spray recommended for ECB on pre-tassel corn
Cape Elizabeth I 0 0 0 3% No spray recommended
Cape Elizabeth II 6 12 1 20% One spray recommended for ECB on pre-tassel corn
Dayton 3 1 1% 6-day spray interval recommended on all silking corn
Farmington 2 1 0 2% No spray recommended
Lewiston 0 0 0 0% No spray recommended
Livermore Falls 1 0 0 28% One spray recommended for ECB on pre-tassel corn
New Gloucester 0 0 1 0% No spray recommended
Nobleboro 2 11 0 18% No spray recommended (no silking corn)
No. Berwick 3 13 0 6-day spray interval recommended on all silking corn
Oxford 1 1 0 6% No spray recommended (no silking corn)
Warren 0 0 0 4% No spray recommended
Wells I 2 0 0 0% No spray recommended (no silking corn)
Wells II 3 4 0 4% 6-day spray interval recommended on all 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.

IPM Web Pages:

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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