Sweet Corn IPM Newsletter No. 9 — August 9, 2024
HIGH CORN EARWORM NUMBERS CONTINUE
Fall Armyworm Also Threatens Corn in Many Fields
SITUATION
Pest pressure for silking corn continued to increase this week with high numbers of corn earworm and fall armyworm found in many fields. This will mean tighter spray intervals for many growers in fresh silking fields to keep ears from being infested. On the bright side, both European corn borer and Western bean cutworm moth counts declined in nearly all locations. The remains of tropical storm Debby may bring a fresh wave of corn earworm and fall armyworm into New England, so growers should be prepared for even higher pest pressure by early next week.
European corn borer: Only one moth was caught among all of our pheromone traps this week, so no sites were over the spray threshold for moths in silking corn. Very little larval feeding damage was found in pre-silking corn, and no sites were over threshold.
Corn earworm: Moth captures were higher at most locations this week, indicating growers should maintain a tight spray schedule on all fresh silking corn to prevent infestation. A 6-day spray interval for silking corn was recommended in Palmyra; a 5-day spray interval was recommended in Bowdoinham and Garland; a 4-day spray interval was recommended for Auburn, Biddeford, Dayton, Lewiston and Wells; a 3-day spray schedule was recommended in Cape Elizabeth and Gray.
Fall armyworm: Moth counts in pheromone traps were variable by location this week. Auburn, Biddeford, Cape Elizabeth, Dayton, Gray, and one site in Wells were over the three-moth threshold for silking corn in pheromone traps, but all sites are presently under a spray interval for corn earworm, which should provide control of fall armyworm. Larval feeding damage was moderate in most pre-silking corn, but sites in Auburn, Biddeford, Bowdoinham, Gray and Cape Elizabeth were over threshold of 12-15% of plants with fresh injury.
Western Bean Cutworm: Captures of moths in pheromone traps were much lower at most locations this week, ranging from one to 19 moths in a trap. This agrees with the pattern we have observed in the past for western bean cutworm; a quick emergence and peak in the population then a rapid decline. Sprays for corn earworm or fall armyworm should protect silking corn from western bean cutworm, and no additional controls were recommended.
Squash vine borer: Moth numbers in pheromone traps were below threshold at all locations this week, and no sprays were recommended. While this could indicate the end of the first generation of squash vine borer for the season, we sometimes see a second generation emerge late in the season to threaten late planted squash.
Potential for Cucurbit Downey Mildew: The remnants of hurricane Debby coming up the coast are likely to bring spores of downy mildew with it. Downy mildew was reported on cantaloupe in western Massachusetts, Pennsylvania and New York over the past two weeks. The strain identified primarily infects cucumber and cantaloupes. Producers of these crops should consider applying protectant fungicides prior to any future storms. These are listed in the New England Vegetable Management Guide – go to the crops tab and select the appropriate cucurbit crop(s). Monitor your crops and keep an eye out for symptoms. Excellent photos and more information can be found here on the Cucurbit Downey Mildew factsheet. If you suspect you have downey mildew infections, please take photos and send them to your local extension specialist or to the UMaine Plant Diagnostic Lab.
Save the Date!
The New England Vegetable & Fruit Conference will be held in Manchester, NH December 17, 18, 19, 2024. Program and registration information will be coming soon. Visit the website: http://www.newenglandvfc.org/
Sincerely,
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm
P.O. Box 179
52 U.S. 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
| Location | CEW Moths | ECB Moths | FAW Moths | WBC Moths | %Feeding Damage | Recommendations / Comments |
|---|---|---|---|---|---|---|
| Auburn | 37 | 0 | 7 | 18 | 19% | 4-day spray interval for silking corn |
| Biddeford | 38 | 0 | 5 | 0 | 20% | 4-day spray interval for silking corn |
| Bowdoinham | 6 | 0 | 2 | 3 | 14% | 5-day spray interval for silking corn |
| Cape Elizabeth | 116 | 0 | 17 | 2 | 52% | 3-day spray interval for silking corn |
| Dayton | 81 | 0 | 6 | 9 | 3% | 4-day spray interval for silking corn |
| Farmington | ||||||
| Garland | 7 | 0 | 1 | 0% | 5-day spray interval for silking corn | |
| Gray | 103 | 0 | 29 | 13 | 6% | 3-day spray interval for silking corn |
| Lewiston | 42 | 1 | 1 | 3 | 1% | 4-day spray interval for silking corn |
| Monmouth | ||||||
| Oxford | ||||||
| Palmyra | 2 | 0 | 1 | 2% | 6-day spray interval for silking corn | |
| Wayne | ||||||
| Wells I | 49 | 0 | 1 | 2 | 2% | 4-day spray interval for silking corn |
| Wells II | 20 | 0 | 23 | 1 | 0% | 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
CBW: Western bean cutworm
| 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.
IPM Web Pages:
Explore Integrated Pest Management in Maine — UMaine
Integrated Pest Management Data Visualization Tool — Penn State
Integrated Pest Management — UMass Amherst
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