Sweet Corn IPM Newsletter No. 11 – September 1, 2017

Sweet CornSweet Corn IPM Newsletter No. 11 – September 1, 2017

Click on photos to enlarge.


Anticipated Storm Fronts May Increase Moth Counts Next Week


Cool night temperatures have slowed development of late corn, but supply and quality look good for the holiday weekend. Many farms will soon be harvesting their last plantings of the season. The cool temperatures appear to have slowed pest activity as well, although most locations still require some protection on silking corn. The remnants of the tropical storm Harvey may drop rain and moths on Maine this weekend, so we may see a different situation next week.

Fall Armyworm on Corn Silk
Fall Armyworm on Corn Silk; photo by David Handley

European corn borer:  Low moth numbers this week, with most locations having caught none, and no locations over the threshold for silking corn. Larval feeding injury on younger corn was also low, but more small larvae were seen in pre-tassel to tasseling corn.

Corn earworm:  Moth counts are fairly low for this time of year in most locations, with several sites catching no moths. However, some sites remain on a tight spray schedule for silking corn. A 6-day spray interval for corn earworm was recommended for silking fields in Garland, Monmouth and Sabattus. A 5-day spray schedule was recommended in Wells. A 4-day spray interval was recommended in Biddeford, Cape Elizabeth, North Berwick, and Poland Spring.

Fall armyworm:  Moth activity remained high at many sites, well over the 3-moth threshold for silking corn. A spray for fall armyworm on silking corn was recommended in Lewiston, Oxford Palmyra and Wales. Other sites, including Auburn, Monmouth, Cape Elizabeth, North Berwick, Poland Spring and Sabattus were also over the 3-moth threshold, but are on a spray schedule for corn earworm. Larval feeding damage in younger corn fields in Cape Elizabeth and Oxford were over the 15% injury threshold, and sprays for pre-tassel to tassel corn were recommended.

Birds, etc.: Flocking species of blackbirds are starting to cause damage in cornfields around the state. Birds may be more of a problem in dry years, when food and water are more difficult to find. They are especially attracted to fields where corn has been allowed to get over-mature. Deer, skunks and raccoons have also been troublesome this year. For information on wildlife problems and management options, you may call the APHIS office in Augusta at 1.866.487.3297.

Bird Damage on Corn
Bird Damage on Corn; photo by David Handley

Free disposal of unusable pesticides:  The Maine Board of Pesticides Control (BPC) and the Maine Department of Environmental Protection (DEP) are sponsoring the Obsolete Pesticides Collection Program. This free program is open to homeowners, family-owned farms and greenhouses. Collections of unwanted pesticides will occur at four sites: Presque Isle, Bangor, Augusta, and Portland. Participants must pre-register by September 29, 2017Drop-ins are not permitted. To register, get details, and learn important information about the temporary storage and transportation of obsolete pesticides, go to the Maine BPC web site or call 207.287.2731.


David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm, P.O. Box 179, 52 US Route 202, Monmouth, ME 04259, 207.933.2100

UMaine Extension Diagnostic Research Lab, Pest Management Unit, 17 Godfrey Drive, Orono, ME 04473, 1.800.287.0279

Sweet Corn IPM Weekly Scouting Summary

Location CEW
Recommendations / Comments
Auburn 9 0 15 4-day spray interval recommended on all silking corn
Biddeford 18 0 4-day spray interval recommended on all silking corn
Bowdoinham 0 1 0 No spray recommended
Cape Elizabeth I 14 1 22 0% 4-day spray interval recommended on all silking corn
Cape Elizabeth II 30 0 29 26% 4-day spray interval recommended on all silking corn
Charleston 0 0 0 No spray recommended
Dayton I 0 0 0 0% No spray recommended
Lewiston 1 0 5 One spray for FAW
Garland 2 1 0 6-day spray interval recommended on all silking corn
Levant 0 3 0 7% No spray recommended
Monmouth 2 1 16 6-day spray interval recommended on all silking corn
Nobleboro 1 2 2 No spray recommended
North Berwick 19 0 9 3% 4-day spray interval recommended on all silking corn
Oxford 0 0 11 15% One spray for FAW
Palmyra 0 0 3 0% One spray for FAW
Poland Spring 19 0 19 14% 4-day spray interval recommended on all silking corn
Sabattus 3 3 19 6-day spray interval recommended on all silking corn
Wales 0 0 9 One spray for FAW on all silking corn
Wayne 0 0 2 No spray recommended
Wells 4 2 1 6% 5-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:
UMaine Cooperative Extension Integrated Pest Management
Penn State Pest Watch for Sweet Corn
UMass Amherst Integrated Pest Management

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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