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PEST PRESSURE MODERATE AS CORN HARVEST BEGINS
Corn Earworm and Fall Armyworm Counts Low, but Still Threaten Silking Corn
Corn harvest is getting into full swing in southern Maine. High winds associated with the numerous thunderstorms have caused minor lodging in some fields. Excessive rainfall may also result in poor herbicide performance and leaching of fertilizer, especially nitrogen. Pest numbers remain relatively moderate, although silking corn in most locations requires protection against corn earworm and/or fall armyworm.
European corn borer: Moth counts continue to decline this week, suggesting that the first generation of this insect may be coming to an end. Most sites had no moths in the traps and none were over the threshold of 5 moths per week in silking corn. European corn borer feeding damage also was not over threshold in any pre-tassel to tasseling fields we scouted this week.
Corn earworm: Corn earworm remains widely distributed but moth counts are still moderate. A 6-day spray interval was recommended for corn earworm on silking fields in Dayton, Garland, Gray, Monmouth, New Gloucester, Nobleboro, North Berwick, Oxford and Palmyra. A 5-day spray interval was recommended for Biddeford, one Cape Elizabeth site, Charleston, Levant, Lewiston, Sabattus, Warren and one Wells location.
Fall armyworm: Moth counts are variable around the state this week. Fields in Biddeford, Cape Elizabeth, Dayton, Garland, Levant, Lewiston, Monmouth and Warren exceeded the threshold of 3 moths per week in silking corn. However, only the Garland site and one Lewiston site were not on a spray regime for corn earworm. Feeding damage on plants was only noted in New Gloucester this week, but did not exceed the 15% damage threshold.
Squash vine borer moths were caught in pheromone traps in Biddeford, Dayton, New Gloucester and Wells this week. The threshold of five moths per week was exceeded at the Biddeford, Dayton and New Gloucester sites. Vine borers threaten summer squash, winter squash and pumpkins. See the New England Vegetable Management Guide for control options.
Corn Rust: Rust is a fungus disease that causes reddish-brown pustules to form on the leaves, stalks and husks, reducing the visual quality of the ears. Severe infections can reduce ear size, especially if they occur prior to tasseling. Typically, corn rust does not become a problem until late in the season, because it can’t overwinter in Maine and must move in from the south. 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 Bravo®, Quilt® and maneb/mancozeb.
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
Sweet Corn IPM Weekly Scouting Summary
|Recommendations / Comments|
|Biddeford||4||4||11||6%||5-day spray interval recommended on all silking corn|
|Bowdoinham||0||0||0||0%||No spray recommended|
|Cape Elizabeth I||7||2||3||0%||5-day spray interval recommended on all silking corn|
|Cape Elizabeth II||0||1||43||One spray recommended for FAW on silking corn|
|Charleston||6||0||0||5-day spray interval recommended on all silking corn|
|Dayton||3||0||5||6-day spray interval recommended on all silking corn|
|Farmington||0||0||0||0%||No spray recommended|
|Garland||2||0||5||2%||6-day spray interval recommended on all silking corn|
|Gray||3||0||0||13%||6-day spray interval recommended on all silking corn|
|Levant||4||0||5||3%||5-day spray interval recommended on all silking corn|
|Lewiston I||7||0||4||3%||5-day spray interval recommended on all silking corn|
|Lewiston II||0||0||4||One spray recommended for FAW on silking corn|
|Livermore Falls||0||0||0||1%||No spray recommended|
|Monmouth||2||1||12||9%||6-day spray interval recommended on all silking corn|
|New Gloucester||2||0||0||3%||6-day spray interval recommended on all silking corn|
|Nobleboro||2||0||6-day spray interval recommended on all silking corn|
|No. Berwick||3||0||0||6-day spray interval recommended on all silking corn|
|Oxford||2||0||1||8%||6-day spray interval recommended on all silking corn|
|Palmyra||2||2||0||5%||6-day spray interval recommended on all silking corn|
|Sabattus||5-day spray interval recommended on all silking corn|
|Warren||5||0||8||1%||5-day spray interval recommended on all silking corn|
|Wells I||1||0||0||0%||No spray recommended|
|Wells II||5||0||2||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.
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