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Sweet Corn IPM Newsletter No. 11 – September 6, 2018

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Sweet CornSweet Corn IPM Newsletter No. 11 – September 6, 2018
Click on photos to enlarge.

Last Issue for 2018!

MAJOR CORN EARWORM FLIGHT THREATENS LATE CORN

Any Late Silking Fields Remaining Require Tight Spray Interval

This will be the final issue of the Sweet Corn IPM Newsletter for the 2018 season. I would like to thank all of the growers who participated in the program this year, and our team of IPM scouts, including Lindsey Ridlon, Althea Hicks, Megan Knowles and Sean McAuley. Have questions, comments or suggestions about the program? Please call or email us.

SITUATION
Many farms will be finishing up corn harvest this week or next, as more hot, humid weather has hastened corn maturity and shortened the harvest season. Recent weather fronts from the west and south have brought a major flight of corn earworm and, to a lesser extent, fall armyworm into the state, most notably in southern and coastal sites. As a result, any late silking corn remaining will need to be protected regularly and often until the silks are completely dry.

European corn borer:  Although we started removing borer traps from fields last week, farms with traps remaining showed very little activity. Single moths were caught in traps in North Berwick, Wells and Sabattus. No sites were over the 15% spray threshold for larval feeding damage. Here’s another reminder to plow down your corn stalks after harvest. Plowing down the stalks destroys overwintering sites for European corn borer.

Corn Field Plowed Down

Corn Field Plowed Down, photo by David Handley

Oats Cover Crop

Oats Cover Crop, photo by David Handley

Corn earworm:  This week saw a significant jump in the number of moths found in our traps, indicating a severe threat to any silking corn remaining. Southern and coastal sites are being hardest hit, with some traps capturing over 100 moths. A 6-day spray interval for silking corn was recommended for Lewiston and Palmyra. A 5-day spray interval was recommended for Levant. A 4-day spray interval was recommended for silking fields in Charleston, Corinth, Dayton, Monmouth, New Gloucester, Nobleboro, Oxford, Poland Spring, Sabattus, Wayne and Wells. A 3-day spray interval was recommended for North Berwick, Biddeford and Cape Elizabeth.

Corn Earworm Feeding on Corn

Corn Earworm Feeding on Corn, photo by David Handley

Fall Armyworm Eggs on Corn

Fall Armyworm Eggs on Corn, photo by David Handley

Fall armyworm:  Armyworm moth numbers were higher at nearly all locations this week, similar to corn earworm. Fields in Biddeford, Cape Elizabeth, Dayton, Levant, Lewiston, Monmouth, New Gloucester, Nobleboro, North Berwick, Oxford, Poland Spring, Wayne and Wells were all over the three moths per week spray threshold for silking corn.

Sincerely,

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                 UMaine Extension Diagnostic Research Lab
P.O. Box 179                        Pest Management Unit
52 U.S. Route 202              17 Godfrey Drive
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
Recommendations / Comments
Biddeford 149 0 26 3-day spray interval recommended on all silking corn
Bowdoinham 1 2 No spray recommended
Cape Elizabeth I 113 0 23 3-day spray interval recommended on all silking corn
Cape Elizabeth II 500+ 121 3-day spray interval recommended on all silking corn
Charleston 15 0 0 4-day spray interval recommended on all silking corn
Corinth 13 0 0 4-day spray interval recommended on all silking corn
Dayton 73 0 19 4-day spray interval recommended on all silking corn
Levant 5 0 4 5-day spray interval recommended on all silking corn
Lewiston 2 0 8 6-day spray interval recommended on all silking corn
Monmouth 15 10 4-day spray interval recommended on all silking corn
New Gloucester 75 41 4-day spray interval recommended on all silking corn
Nobleboro 11 4 4-day spray interval recommended on all silking corn
North Berwick 112 1 3-day spray interval recommended on all silking corn
Oxford 8 96 4-day spray interval recommended on all silking corn
Palmyra 2 1 0 6-day spray interval recommended on all silking corn
Poland Spring 71 6 4-day spray interval recommended on all silking corn
Sabattus 11 1 1 4-day spray interval recommended on all silking corn
Wayne 36 13 4-day spray interval recommended on all silking corn
Wells I 11 0 1 4-day spray interval recommended on all silking corn
Wells II 64 0 38 4-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
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.

The University of Maine is an equal opportunity/affirmative action institution.

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