Sweet Corn IPM Newsletter – No. 9 – August 19, 2022

Sweet Corn IPM Newsletter  No. 9 August 19, 2022

PEST PRESSURE LOWER THIS WEEK

Corn Earworm, Fall Armyworm Numbers Still Require Protection of Silking Corn

 

SITUATION

Some much-needed rain and cooler night temperatures over the past week have helped corn development and reduced insect pressure in most fields.  However, moth counts of corn earworm, fall armyworm and European corn borer are still high enough at most locations to require all silking corn be treated to prevent infestation.

European corn borer:  Larval feeding injury from corn borer remains low and was not over the 15% control threshold for pre-tassel corn at any of our scouting sites. However, when combined with fall armyworm feeding, several farms were over threshold in younger corn (see Fall armyworm below).  Moth captures were spotty, but still higher than previous weeks in most locations. Counts were over the 5-moth threshold for silking corn in Bowdoinham, Farmington, Lewiston, Monmouth, Oxford, and Sabattus. Only the Farmington site was not on a spray interval for corn earworm, so an additional spray was recommended there.  These numbers suggest that a second generation of corn borer is now underway.

Corn earworm:  Moth counts are mostly lower than last week, but were high enough to continue tight spray intervals for silking corn at most locations. A 6-day spray interval for fresh silking corn was recommended in Monmouth, Oxford and Palmyra.  A 5-day spray schedule was recommended for Biddeford, Garland, and Sabattus.   A 4-day spray interval was recommended in Bowdoinham, Cape Elizabeth, Dayton, Lewiston, New Gloucester and Wells.

Fall armyworm:  Fall armyworm remained high at most sites this week, but its distribution is variable.   Trap counts were over the three-moth threshold for silking corn in Biddeford, Bowdoinham, Cape Elizabeth, one Dayton site, Farmington, Lewiston, Monmouth, New Gloucester, Oxford, and one Wells site.  With the exception of Farmington, all of these sites are on a spray interval for corn earworm, so additional sprays should not be needed. A single spray for silking corn was recommended in Farmington.  Larval feeding damage on leaves and tassels of younger corn was over threshold in several locations, and growers should continue to scout fields not yet silking for injury.  When combined with any European corn borer injury found, the control threshold is 13% of plants showing injury.  Sprays for feeding damage were recommended in Biddeford, Bowdoinham, Cape Elizabeth, Dayton, Oxford, and Wells.

Western bean cutworm:  Moths numbers fell at all locations this week.  The highest numbers were in western Maine, and no traps had more than 19 moths, most with fewer than 10.  Fields under a spray interval for corn earworm will also be protected against this pest.

Cucurbit downy mildew reported in Maine: There has been a report of cucurbit downy mildew on cucumbers in Kennebec County this week.  This is a very serious disease of cucumbers and melons, and growers should be on the lookout for symptoms in their fields.  Consult the New England Vegetable Management Guide for details;

https://nevegetable.org/crops/disease-control-7.

 

Sincerely,

David T. Handley

David T. Handley

Vegetable & 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	Recommendations / Comments
Biddeford	4	0	27	30%	5-day spray interval for silking corn
Bowdoinham	10	10	41	26%	4-day spray interval for silking corn
Cape Elizabeth	30	3	18	17%	4-day spray interval for silking corn
Dayton I	17	0	2		4-day spray interval for silking corn
Dayton II	21	3	4	17%	4-day spray interval for silking corn
Farmington	0	11	8		One spray on silking corn for FAW + ECB
Garland	5	0	0	0%	5-day spray interval for silking corn
Lewiston	22	8	3		4-day spray interval for silking corn
Lewiston II	32	8	15		4-day spray interval for silking corn
Monmouth	2	7	8		6-day spray interval for silking corn
New Gloucester	42	0	34	1%	4-day spray interval for silking corn
Oxford	2	8	17	13%	6-day spray interval for silking corn
Palmyra	2	0	0	0%	6-day spray interval for silking corn
Sabattus	4	9	0	8%	5-day spray interval for silking corn
Wayne	0	1	1	0%	No spray recommended
Wells I	11	0	1	8%	4-day spray interval for silking corn
Wells II	24	1	8	22%	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

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 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/

https://nevegetable.org/crops

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