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Sweet Corn IPM Newsletter No. 10 – August 25, 2017

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Sweet Corn IPM Newsletter No. 10 – August 25, 2017
Click on photos to enlarge.

INSECT NUMBERS RISE, INCREASING THREAT

Corn Earworm, Fall Armyworm, European Corn Borer Moth Counts Higher

SITUATION
Fine weather has kept corn development at a good pace, and supply is improving. Quality has been very good in fields where growers have been able to irrigate. Pests that normally emerge later in the season, such as rust and aphids are starting to show up in many fields.

European corn borer:  Moth counts continue to be spotty, with many locations having no moths, but two having counts over the threshold for silking corn. Fields in Wayne and Poland Spring were over the 5-moth threshold for silking corn. Larval feeding injury was still low, but more small larvae are starting to show up in pre-tassel corn.

Corn earworm:  Moth counts were generally higher in most locations this week, calling for a tighter spray schedule for silking corn in most fields, although a few locations had no moths, including Monmouth, Farmington, Oxford, Levant and Palmyra. A 6-day spray interval for corn earworm was recommended for silking fields in Wales and Garland. A 5-day spray schedule was recommended in Bowdoinham, Charleston, Lewiston and one Wells site. A 4-day spray interval was recommended in Auburn, Biddeford, Cape Elizabeth, one Dayton site, Nobleboro, North Berwick, and one Wells site.

Corn Earworm Moth

Corn Earworm Moth, photo by David Handley

Fall Armyworm Moths

Fall Armyworm Moths (female right, male left), photo by James Dill

Fall armyworm:  Similar to corn earworm, moth counts were mostly higher this week, with many sites over the 3-moth threshold for silking corn. A spray for fall armyworm on silking corn was recommended at one site in Dayton, Monmouth, New Gloucester, Oxford and Sabattus.  Other sites, including Auburn, Biddeford, Cape Elizabeth, Lewiston, Nobleboro, and Wells were also over the 3-moth threshold, but are on a spray schedule for corn earworm. Larval feeding damage in younger corn was lower this week. Fields in Biddeford, and Wells were over the 15% injury threshold, and sprays for pre-tassel to tassel corn were recommended.

Corn leaf aphids have been observed in many fields this week. Colonies of these small, bluish-green insects can cover the tassels, stalks and husks. The aphids excrete a “honeydew” on the leaves and husks, which stimulates the development of sooty mold fungus. This dark, slimy coating greatly reduces the visual appeal of the ears. Sprays applied for corn earworm usually control aphids.

Aphids on corn

Aphids on Corn, photo by Kaytlin Woodman

Rust on Corn

Rust on Corn, photo by David Handley

Corn rust:  We have also seen corn rust in many fields this week. Rust is a fungus disease that causes reddish-brown pustules to form on the leaves and husks, reducing the quality of the ears. Typically, corn rust does not become a problem until late in the season. A fungicide spray for rust would only be recommended if the infection were noticed in a field prior to tasseling. Later infections are unlikely to cause enough damage to the crop to justify control measures. Materials available to control corn rust include Quadris®, Bravo®, and Quilt®.

Spotted wing drosophila:  Numbers continue to increase in fields with ripe berry fruit. Regular sprays (every 5-7 days) will be needed to prevent raspberries, blueberries and day neutral strawberries from becoming infested with larvae. Visit our Spotted Wing Drosophila blog for more information.

Sincerely,

David T. Handley
Vegetable and 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
Moths
ECB
Moths
FAW
Moths
%Feeding
Damage
Recommendations / Comments
Auburn 18 0 21 4-day spray interval recommended on all silking corn
Biddeford 13 1 22 24% 4-day spray interval recommended on all silking corn
Bowdoinham 6 0 2 5-day spray interval recommended on all silking corn
Cape Elizabeth I 28 2 19 6% 4-day spray interval recommended on all silking corn
Cape Elizabeth II 20 3 11 14% 4-day spray interval recommended on all silking corn
Charleston 4 0 2 5-day spray interval recommended on all silking corn
Dayton I 1 0 4 One spray on silking corn for FAW
Dayton II 19 0 12 8% 4-day spray interval recommended on all silking corn
Farmington 0 4 0 No spray recommended
Lewiston 6 0 9 5-day spray interval recommended on all silking corn
Garland 2 0 0 1% 6-day spray interval recommended on all silking corn
Levant 0 0 0 2% No spray recommended
Monmouth 0 0 5 1% One spray on silking corn for FAW
New Gloucester 0 67 5% One spray on silking corn for FAW
Nobleboro 8 0 9 4-day spray interval recommended on all silking corn
North Berwick 32 0 9 0% 4-day spray interval recommended on all silking corn
Oxford 0 0 5 3% One spray on silking corn for FAW
Palmyra 0 0 0 0% No spray recommended
Poland Spring 6 One spray on silking corn for ECB
Sabattus 1 1 3 One spray on silking corn for FAW
Wales 2 0 2 2% 6-day spray interval recommended on all silking corn
Wayne 1 5 0 One spray on silking corn for ECB
Wells I 9 0 3 17% 4-day spray interval recommended on all silking corn
Wells II 6 4 24 8% 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 IPM
Penn State Sweet Corn IPM
UMass Extension IPM Programs

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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