Sweet Corn IPM Newsletter No. 8- August 21, 2020

Sweet Corn

Sweet Corn IPM Newsletter  No. 8   – August 21, 2020

Click on photos to enlarge.

CORN EARWORM COUNTS LOWER, STILL A THREAT TO SILKING CORN

Fall Armyworm Counts Remain High, Despite Cooler Night Temperatures

 

SITUATION

Another dry week for most fields. Irrigation has helped  keep corn quality high, despite the lack of rain. Cooler night temperatures should slow development and spread out maturity on later ripening fields.  Cooler nights can also reduce insect activity; we generally saw lower moth counts this week, but populations were still high enough to warrant protecting silks in nearly all fields.

 

European Corn Borer Larva on Ear
European Corn Borer Larva on Ear, photo by David Handley

European corn borer:

Larval feeding injury was not over the 15% control threshold for pre-silking corn at any location scouted this week. Moth counts were higher at many sites, and over the weekly threshold of five for silking corn in Poland Spring and Sabattus, indicating a second generation is now emerging.

 

 

 

 

 

Corn earworm:

Corn Earworm Moth
Corn Earworm Moth; photo by David Handley

Although moth captures were down from last week’s season high numbers, counts were still high enough to warrant a tight spray interval on silking corn at most locations.  A three-day spray interval for silking corn was recommended at one Cape Elizabeth site.   A four-day interval was recommended in Auburn, Biddeford, Bowdoinham, Dayton, New Gloucester, Poland Spring, Wayne, Wells and one Cape Elizabeth site. A five-day spray interval was recommended in Lewiston, Monmouth, Sabattus and one Wells site. A six-day spray interval was recommended in Corinth.

 

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

 

Fall armyworm (FAW):

Moth captures were generally lower this week, but still high enough to recommend protection for silking corn not currently under a spray interval for corn earworm. Counts exceeded the three-per-week threshold for silking corn in: Auburn, Biddeford, Cape Elizabeth, Dayton, Monmouth, New Gloucester, Oxford, Poland Spring, Wayne and Wells. Only the Oxford site was not under a spray interval for corn earworm, so a spray for FAW on silking corn was recommended. Fall armyworm larval feeding damage on pre-silking corn exceeded the 15% threshold in Biddeford, Cape Elizabeth, Dayton, Oxford and Poland Spring.

 

Western bean cutworm moth
Western Bean Cutworm Moth; photo by Lindsey Ridlon

Western Bean Cutworm:

Moths counts were much lower at most locations this week, but still at threatening levels in some sites, including; Auburn (1), Biddeford (2), Bowdoinham (1) Cape Elizabeth (1), Dayton (6), New Gloucester (6), Oxford (6), Sabattus (3), Wayne (8) and Wells (10). All locations, except Oxford, are spraying for corn earworm, which should protect corn from western bean cutworm.

 

 

Three Squash Vine Borer Moths
Three Squash Vine Borer Moths; photo by Lindsey Ridlon

 

Squash vine borer:

Counts were low this week; Biddeford (1), Oxford (1) and Wells (1). None of the sites were over the threshold of five moths per week, so no sprays were recommended.

 

 

 

 

 

Spotted wing drosophila:

Drosophila Trap
Drosophila Trap, photo by David Handley

Very high traps counts at nearly all locations this week, indicate a very high threat level for any ripening fruit remaining in berry fields. Growers should maintain a tight, regular (5-7 day) spray schedule to prevent larvae from infesting fruit. For more information visit our website:   Highmoor Farm News Blog

 

Sincerely,

David T. Handley

Vegetable and Small Fruit Specialist

 

Highmoor Farm                      Pest Mgmt. Unit

P.O. Box 179                           17 Godfrey Drive

52 U.S. Route 202                   Orono, ME  04473

Monmouth, ME  04259          1.800.287.0279

207.933.2100

 

Sweet Corn IPM Weekly Scouting Summary

Location CEW

Moths

ECB

Moths

FAW

Moths

%Feeding

Damage

Recommendations / Comments
Auburn 17 0 35 4-day spray interval for all silking corn
Biddeford 12 2 41 17% 4-day spray interval for all silking corn
Bowdoinham 21 3 38 4-day spray interval for all silking corn
Cape Elizabeth I 17 0 20 4-day spray interval for all silking corn
Cape Elizabeth II 109 3 15 25% 3-day spray interval for all silking corn
Charleston 0 0 0 No spray recommended
Corinth 2 0 0 1% 6-day spray interval for all silking corn
Dayton I 46 4 41 0% 4-day spray interval for all silking corn
Dayton I 17 3 71 21% 4-day spray interval for all silking corn
Lewiston 7 0 0 5-day spray interval for all silking corn
Levant 1 0 0 1% No spray recommended
Monmouth 4 3 12 5-day spray interval for all silking corn
New Gloucester 24 0 120 3% 4-day spray interval for all silking corn
Oxford 1 0 43 16% One spray on silking and pre-silking corn for FAW
Palmyra 0 0 0 No spray recommended
Poland Spring 12 34 17 18% 4-day spray interval for all silking corn
Sabattus 7 10 5-day spray interval for all silking corn
Wayne 51 2 41 9% 4-day spray interval for all silking corn
Wells I 7 0 18 5-day spray interval for all silking corn
Wells II 20 0 12 4-day spray interval for 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 the 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 Pest Management

Pest Watch

UMass IPM

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