Sweet Corn IPM Newsletter No. 4 – July 15, 2022

shucked ears of sweet corn

Sweet Corn IPM Newsletter – No. 4 – July 15, 2022

COOL NIGHTS SLOW PEST ACTIVITY

Fall Armyworm and Western Bean Cutworm Numbers Increasing

SAVE THE DATE! Highmoor Summer Tour: 1:30 ​- ​Pomological Society Meetings and Tour ($10), ​5:00 – Supper ($25/person) is served, 6​:00​ ​- ​Vegetable and Small Fruit Tour ​(free). ​(If you just want to attend the Vegetable tours, you don’t need to register.)​ For More Information and to Register

SITUATION

Most of the state remains in very dry conditions but most fields that can be irrigated are getting adequate water and show good growth.  Early silking corn in southern Maine is nearing maturity, so local corn should soon be showing up on farm stands soon.  Recent cool night temperatures appear to have slowed evening flights of moths, so pheromone trap catches were down this week, reducing the need for spray coverage.

European Corn Borer Larva
European Corn Borer Larva; photo by David Handley

European corn borer:  Larval feeding injury was not over the 15% control threshold for pre-tassel corn at any of our scouting sites, although low-level feeding activity was observed in most fields. Moth activity was also lower, with no sites over the 5-moth threshold for silking corn.

 Corn earworm:  Although much more silking corn is now available, moth counts were lower this week, most likely a result of cool evening temperatures, which reduced moth activity.  A 6-day spray interval for fresh silking corn was recommended in Cape Elizabeth, and at one Wells site.  All other sites were below threshold.

 Fall armyworm:  Fall armyworm moths were over the three-moth threshold for silking corn in Biddeford and New Gloucester.  Both sites were not on a spray interval for corn earworm, so a spray to protect silking corn was recommended.  As expected, larval feeding damage on leaves and tassels was more widespread this week but was not yet over threshold at any site.

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

Western Bean Cutworm:  We’ve caught moths of this “new” pest at several locations this week.  The larvae of western bean cutworms feed on corn plants and move into the ears through the silk channels or the husks, similar to fall armyworm. The threshold for feeding injury on plants is 8%.  Sprays for corn earworm should protect silking corn from western bean cutworm as well. The optimal time for controlling the larvae is late pre-tassel to tassel when they move from the leaves and stalk into the ears.

Squash vine borer: Moths continue to be caught at all of our trapping sites this week, with numbers ranging from 7 to 31.  Sprays are recommended when more than 5 moths are caught in a pheromone trap in a week, so it is likely that a spray is needed on all susceptible squash and pumpkins to prevent infestation. If you are not using pheromone traps, initiate control when you see the moths, or damage on plants.  See the New England Vegetable Management Guide for control options.

Male and Female Spotted Wing Drosophila Flies
Male (left) and Female (right) Spotted Wing Drosophila; photo by Griffin Dill. Actual size: 2-3 mm.

Spotted wing drosophila alert:  We are now catching spotted wing drosophila in traps set up in berry fields. These small fruit flies can cause serious fruit losses in late strawberries, raspberries, blueberries, and other soft fruits.  For more information visit our website:

http://extension.umaine.edu/highmoor/news-events/.

Cornfield at Highmoor Farm
Cornfield at Highmoor Farm, photo by David Handley

Highmoor Farm, the Maine Agriculture and Forest Experiment Station in Monmouth will hold a summer tour and BBQ dinner on Wednesday, July 27, from 1:30 to 7:30 p.m.  For information and registration go to:

Summer Tour at Highmoor Farm

Sincerely,

 

David T. Handley

Vegetable and Small Fruit Specialist

 

Highmoor Farm             UMaine Extension Diagnostic

P.O. Box 179                 Research Lab, Pest Mgmt. Unit

52 U.S. Route 202          17 Godfrey Drive

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

Recommandations / Comment
Biddeford 0 0 3 13% One spray on silking corn for FAW
Bowdoinham 1 4 2 12% No spray recommended
Cape Elizabeth 3 0 0 2% 6-day spray interval for silking corn
Dayton I 0 0 0 4% No spray recommended
Dayton II 1 3 1 10% No spray recommended
Farmington 0 2 0 2% No spray recommended
Garland 1 0 0 0% No spray recommended
Lewiston 0 0 0 2% No spray recommended
Lewiston II 0 0 0 2% No spray recommended
New Gloucester 1 0 3 0% One spray on silking corn for FAW
Oxford 0 0 0 6% No spray recommended
Sabattus 1 0 0 0% No spray recommended
Wayne 0 0 0 2% No spray recommended
Wells I 2 1 1 5% 6-day spray interval for silking corn
Wells II 1 0 0 4% No spray recommended

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)

ECB: European corn borer

FAW: Fall armyworm

 

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.

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.

 

IPM Web Pages:

http://extension.umaine.edu/ipm/

http://www.pestwatch.psu.edu/sweet_corn.htm

https://ag.umass.edu/integrated-pest-management/

 

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