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Sweet Corn IPM Newsletter No. 8 – August 16, 2013

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Sweet Corn

Sweet Corn IPM Newsletter No. 8 – August 16, 2013

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Moth Counts and Feeding Injury under Spray Thresholds in Most Corn Fields

Our weather continues to be dominated by fronts coming from the west and northwest, which appears to be keeping corn earworm and fall army worm moths from moving into Maine from the south in high numbers.  Most farms continue to enjoy a light spray schedule for this time of the season.

European corn borer:  Moth catches were very low again this week. In some years we may start to see a second generation of European corn borer moths emerge in the late summer, but there has been no indication of that so far this season. No silking fields exceeded the threshold of 5 moths per week. No fields had European corn borer feeding damage over threshold.

Corn earworm:  Moth counts fell slightly to even lower levels than last week in most locations. Many fields do not require a spray interval for silking corn at this time.  A 5-day spray interval was recommended for fields in Monmouth and Charleston. A 6-day spray interval was recommended for silking fields in Cape Elizabeth, Garland, Levant, North Berwick and Wales.

Fall armyworm:  Moth counts are very low for this late in the season. Fall armyworm moths were caught in Biddeford, Cape Elizabeth, one Dayton site, Levant, Lewiston and Wells this week. Only the Biddeford and Dayton sites exceeded the weekly threshold of three moths for silking corn. Sites in Biddeford and Cape Elizabeth had fall armyworm feeding damage on younger corn exceeding the spray threshold of 15%.

Fall Armyworm on Corn Silk

Fall Armyworm on Corn Silk, photo by David Handley

Aphids on Corn Tassel

Aphids on Corn Tassel, photo by Kaytlin Woodman

Aphids:  Some fields are showing infestations of aphids on corn tassels, silks and husks. While aphid feeding is not usually a significant problem, the sooty mold that develops on the husks as a result of their waste (called honeydew), is often objectionable to customers.  Sprays, other than Bt’s or spinosad products, that are used to control other corn pests also offer control of aphids, including Asana®, Capture®, Warrior® and Lannate®.

Late Blight on Tomato Leaf

Late Blight on Tomato Leaf, photo by James Dill

Late Blight:  Grower and Farm Stand Alert
Late blight has been found on tomato plants in coastal Maine (Warren) this week. This follows reports of late blight in tomato and potato plantings in Vermont and New York. Growers should be alert to catch early symptoms and be ready to apply appropriate control measures.  Symptoms include water-soaked lesions on the leaves with fine, white cottony mycelium on the undersides. Infections on the stems appear as dark, almost black lesions. Please report any suspicious symptoms to the Pest Management Office at 581-3883, or email

Spotted Wing Drosophila Alert
Fruit fly counts are still variable around the state, but we are catching flies at most locations now, including Limington, Springvale, Wells, Cape Elizabeth, New Gloucester, Gray, Monmouth, Wales, Livermore Falls, Bowdoinham, Dresden and Warren.  Most traps had fewer than ten flies. The exception was, again, our Bowdoinham site, which had over 100 flies. Once spotted wing drosophila is found in your area, fruit should be protected with a recommended insecticide.  Regular and repeated treatments are needed to keep fruit from becoming infested. Visit our Spotted Wing Drosophila blog for more details.


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 1 0 2% No spray recommended
Biddeford 0 1 6 16% One spray recommended for FAW
Cape Elizabeth 2 2 2 26% 6-day spray interval recommended on all silking corn
Charleston 6 0 0 2% 5-day spray interval recommended on all silking corn
Dayton I 0 0 6 3% One spray recommended for FAW
Dayton II 0 0 0 1% No spray recommended
Farmington 0 0 0 0% No spray recommended
Garland 3 1 0 3% 6-day spray interval recommended on all silking corn
Levant 3 1 1 3% 6-day spray interval recommended on all silking corn
Lewiston 0 0 1 1% No spray recommended
Monmouth 5 0 2 1% 5-day spray interval recommended on all silking corn
New Gloucester 1 2 0 1% No spray recommended
Nobleboro 1 1 0 12% No spray recommended
No. Berwick 2 1 0 3% 6-day spray interval recommended on all silking corn
Palmyra 0 1 0 4% No spray recommended
Sabattus 0 0 0 0% No spray recommended
Wales 2 0 0 6-day spray interval recommended on all silking corn
Warren 1 0 0 5% No spray recommended
Wells 0 0 1 8% 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.

IPM Web Pages:

Where brand names or company names are used it is 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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