Sweet Corn IPM Newsletter No. 5 – July 21, 2017
Highmoor Farm Field Day
Wednesday, July 26, 2017
Save the Date!
INSECT PRESSURE HIGHER; PROTECT SILKING CORN
Corn Earworm & Fall Armyworm Numbers Increasing
High temperatures have pushed sweet corn development, compensating somewhat for earlier cool temperatures. While European corn borer pressure has been decreasing, corn earworm and fall armyworm pressure has been increasing, posing a serious risk to fields now in silk. Synthetic pyrethroid insecticides (FRAC Group 3A) may have a short residual life under hot, sunny conditions, so recommended spray intervals should not be extended unless daily high temperatures fall below 85 degrees for 3 or more consecutive days. For those growers trying Bt-modified corn selections, it is important to note that this protection may not be adequate under very heavy fall armyworm or corn earworm pressure. When moth populations are high, Bt fields should be scouted for injury and treated if necessary.
European corn borer: Moth captures were very low this week, and larval feeding activity is decreasing. No fields were over the recommended spray thresholds. However, fall armyworm larval feeding damage is being noticed in more fields, and is quickly become more of a threat than European corn borer.
Corn earworm: Moth counts increased again this week, and are becoming more widely distributed. More silking fields have been put on spray schedules to protect ears from infestation. A 6-day spray interval for corn earworm was recommended for silking fields in Oxford, Sabattus, Dayton, North Berwick and one Wells site this week. A 5-day spray interval was recommended for silking fields in Auburn, Cape Elizabeth, Garland, and Poland Spring. A 4-day spray interval was recommended in Lewiston.
Fall armyworm: Moth counts rose significantly in many locations this week, indicating that fall armyworm will be an important threat to corn in the coming days and weeks. Feeding damage was found in more fields, but has generally been low to date. Once the corn has reached the silking stage, sprays should be based on captures of moths in pheromone traps to prevent larvae from damaging the ears. If three or more moths are caught in a week in silking fields, a spray is recommended, unless the field is under a spray interval for corn earworm. Sprays for fall armyworm on silking corn were recommended in Biddeford New Gloucester, Wayne and one Wells site this week. Cape Elizabeth and Lewiston were also over the 3-moth threshold, but are under a spray schedule for corn earworm.
Spotted wing drosophila: Fly counts have risen significantly in most of our trapping sites this week. Growers with ripening blueberries, raspberries or other soft fruit should be monitoring for flies and larvae, and should consider protecting all ripening fruit. For details, visit our Spotted Wing Drosophila blog.
Squash vine borer moths were caught in pheromone traps in Wells, Biddeford, Cape Elizabeth, Farmington and Oxford this week. The Biddeford, Cape Elizabeth and Dayton sites were above the 5 moths per week spray threshold, and a spray was recommended. This pest remains active in much of the state. Growers with squash and pumpkins should be on the lookout for vine borer symptoms and protect squash plants if moths or damage are seen.
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
|Recommendations / Comments|
|Auburn||5||0||0||0%||5-day spray interval recommended on all silking corn|
|Biddeford||0||31||12%||One spray recommended for FAW on all silking corn|
|Cape Elizabeth I||4||0||6||0%||5-day spray interval recommended on all silking corn|
|Cape Elizabeth II||6||0||26||10%||5-day spray interval recommended on all silking corn|
|Charleston||0||0||0||0%||No spray recommended|
|Dayton I||3||1||1||6-day spray interval recommended on all silking corn|
|Dayton II||1||0||1||5%||No spray recommended|
|Farmington||1||1||2||2%||No spray recommended|
|Garland||4||0||0||0%||5-day spray interval recommended on all silking corn|
|Lewiston||9||0||29||0%||4-day spray interval recommended on all silking corn|
|Levant||1||0||0||1%||No spray recommended|
|New Gloucester||0||0||41||0%||One spray recommended for FAW on all silking corn|
|Nobleboro||1||0||0||0%||No spray recommended|
|North Berwick||3||1||1||2%||6-day spray interval recommended on all silking corn|
|Oxford||2||0||11||9%||6-day spray interval recommended on all silking corn|
|Palmyra||3||0||0||0%||No spray recommended (no silking corn)|
|Poland Spring||6||0||0||5-day spray interval recommended on all silking corn|
|Sabattus||2||0||0||3%||6-day spray interval recommended on all silking corn|
|Wales||0||0||1||0%||No spray recommended|
|Wayne||1||0||6||0%||One spray recommended for FAW on all silking corn|
|Wells I||1||2||9||1%||One spray recommended for FAW on all silking corn|
|Wells II||3||0||3||1%||6-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
|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.
The University of Maine is an equal opportunity/affirmative action institution.