Sweet Corn IPM Newsletter No. 2 — July 7, 2023
CORN EARWORM THREATENS EARLY SILKING CORN
European Corn Borer, Corn Earworm & Fall Armyworm Moths Caught This Week
Early corn planted under plastic mulch or rowcovers is silking in southern Maine, while early-mid season corn is now between whorl and pre-tassel. Most fields are very wet from all the rain and we are seeing some nutrient deficiencies and herbicide failure as a result. All three of the major corn pests were found in our traps this week, and we are finding corn borer feeding injury in pre-tassel corn.
European corn borer: Larval feeding injury was found in some, but not all, of our sites this week, and none were over the control threshold of 15%. We have not been catching corn borer moths in our traps, but we should start seeing them in the coming week. Sprays during the pre-tassel stage, when both moths and larvae are present, can control larvae before they move into the stalks and ears where they will be protected. Once corn reaches the silk stage, sprays may be based on the number of moths caught in pheromone traps. Moths will lay eggs on flag leaves of silking corn, and the larvae can move into the ears without leaving visible feeding injury. If more than five moths are caught during a week in silking corn, a spray is recommended.
Corn earworm: The arrival of corn earworm this week is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths cannot find silking corn to deposit their eggs on, they may lay eggs on the leaves or tassels of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm. This damage should be counted, along with any borer or armyworm damage, to determine if a pre-silking spray is warranted. A 4-day spray interval for silking corn was recommended for Dayton, Gray, Lewiston, Wayne and Wells. Auburn, Oxford and Farmington were also over threshold for earworm but corn there was not yet in silk.
Fall armyworm: Only a few fall armyworm moths were caught in pheromone traps this week, but no larval feeding damage on leaves or tassels has been found in fields we’ve scouted. Young larvae can move into the ears through the silk channel, behaving similarly to corn earworm. If more than 3 moths are caught in pheromone traps in a field with silking corn, a spray would be recommended, if it is not already being sprayed for corn earworm.
Japanese beetles are now appearing in southern and mid-state areas. These insects often find their way into cornfields and feed on the leaves, causing an interveinal skeletonizing, which is generally not significant. However, they may also feed on the silks of developing ears, causing poor tip fill. Sprays for European corn borer and/or corn earworm (except Bt’s) usually will control Japanese beetle as well.
Squash vine borer: Pheromone traps were set up in pumpkin and squash traps this week. There are reports of vine borer activity in MA and NH. Growers with squash should be on the lookout for vine borer symptoms and protect plants if moths or damage are seen. See the New England Vegetable Management Guide for control options.
David T. Handley
Vegetable & Small Fruit Specialist
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259
UMaine Extension Diagnostic
Research Lab, Pest Mgmt. Unit
17 Godfrey Drive
Orono, ME 04473
|Location||CEW Moths||ECB Moths||FAW Moths||%Feeding Damage||Recommendations / Comments|
|Auburn||24||0||0||0%||No spray recommended (no silking corn)|
|Biddeford||0||0||0||13%||No spray recommended (no silking corn)|
|Bowdoinham||1||0||0||6%||No spray recommended|
|Cape Elizabeth||5||0||0||0%||No spray recommended (no silking corn)|
|Dayton||18||0||0||0%||4-day spray interval for silking corn|
|Farmington||16||0||0||11%||No spray recommended (no silking corn)|
|Gray||31||0||0||0%||4-day spray interval for silking corn|
|Lewiston||48||1||0||0%||4-day spray interval for silking corn|
|Oxford||5||0||0||4%||No spray recommended (no silking corn)|
|Sabattus||8||0||0||0%||One spray for ECB feeding on pre-tassel corn|
|Wayne||17||0||0||9%||4-day spray interval for silking corn|
|Wells||18||0||0||5%||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
|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.
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