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Warm weather has pushed corn maturity along rapidly and supplies are picking up. A steady flow of weather from the south, including some heavy showers in some areas, is keeping corn earworm pressure very high in most fields this week. Several locations are now on a recommended 3-day spray interval, which we don’t typically see until early fall when tropical storms start moving through Maine.
European corn borer: A jump in moth counts in southern Maine suggests an emergence of a second generation of corn borer in that area. High counts continue to be found in more northern locations as well. These moths pose a risk to any silking corn that is not presently being sprayed for corn earworm. Wells, Biddeford, Sabattus, Charleston, Levant, Palmyra, and East Corinth were over the threshold of 5 moths in silking corn. Feeding injury from larvae in whorl to tassel stage corn was low in most locations, with only Biddeford exceeding the 15% feeding injury threshold. North Berwick exceeded the threshold when fall armyworm damage was added to the total.
Corn earworm: Moth counts continue to increase in most locations, putting very high pressure on all silking corn. A 3-day spray interval for fresh silking corn was recommended for Biddeford, North Berwick, and Wells this week. A 4-day spray interval was recommended in Cape Elizabeth, Dayton, Dresden, Levant, Lewiston, Monmouth, Palmyra, Poland Spring, Sabattus, and Warren. A 5-day spray interval was recommended for New Gloucester, East Corinth and Livermore Falls. A 6-day spray interval was recommended for fields in Charleston and Wales.
Fall armyworm: Moth captures remain low for this time of year, although we have started finding larval feeding damage in some southern fields. Only one Cape Elizabeth location exceeded the spray threshold of 3 moths in silking corn, but the field is already under a spray schedule for corn earworm so no additional sprays should be needed. Two fall armyworm moths were caught at Biddeford and our Dayton locations, and a single moth was caught in Dresden this week, below threshold for silking corn. Fall armyworm feeding damage was found in Biddeford, Dayton, and North Berwick, but was below the 15% threshold.
Other Pests of Note:
Picnic beetles can become a problem during the late summer on silking corn. These beetles are about ¼ inch long, black with orange spots. They can often be found on stalks and ears that are infested with European corn borer or fall armyworm, feeding on sap at an entry or exit hole. They will also feed on the silks and may work their way into the silk channel. While the damage is usually insignificant, customers dislike finding the insects in their bags. Sprays to control corn earworm should provide control of these beetles if they are found in your field.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management Office
P.O. Box179 491 College Ave
Monmouth,ME 04259 Orono,ME 04473
|Location||CEW Moths||ECB Moths||FAW Moths||%Feeding Damage||Recommendations / Comments|
|Biddeford||97||25||2||39%||3-day spray interval for all silking corn|
|Cape Elizabeth I||36||2||0||0%||4-day spray interval for all silking corn|
|Cape Elizabeth II||70||0||3||0%||4-day spray interval for all silking corn|
|Charleston||3||12||0||4%||6-day spray interval for all silking corn|
|Dayton I||16||2||0||6%||4-day spray interval for all silking corn|
|Dayton II||34||1||2||10%||4-day spray interval for all silking corn|
|Dresden||14||0||1||5%||4-day spray interval for all silking corn|
|East Corinth||6||0||0||3%||5-day spray interval for all silking corn|
|Farmington||0||1||0||3%||No spray recommended|
|Levant||31||11||0||13%||4-day spray interval for all silking corn|
|Lewiston||11||4||0||2%||4-day spray interval for all silking corn|
|Livermore Falls||7||0||0||6%||5-day spray interval for all silking corn|
|Monmouth||8||0||0||6%||4-day spray interval for all silking corn|
|New Gloucester||6||0||0||0%||5-day spray interval for all silking corn|
|North Berwick||172||4||0||17%||3-day spray interval for all silking corn|
|Palmyra||11||6||0||5%||4-day spray interval for all silking corn|
|Poland Spring||45||1||0||All Silk||4-day spray interval for all silking corn|
|Sabattus||8||10||0||4%||4-day spray interval for all silking corn|
|Wales||2||0||0||0%||6-day spray interval for all silking corn|
|Warren||38||1||0||10%||4-day spray interval for all silking corn|
|Wells I||107||1||0||All Silk||3-day spray interval for all silking corn|
|Wells II||92||5||0||All Silk||3-day spray interval for 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.
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.
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.
Image Description: Sweet Corn
Image Description: European Corn Borer Entry Hole
Image Description: Corn Earworm Larvae
Image Description: Fall Armyworm on Corn Leaf
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