Sweet Corn IPM Newsletter No. 11 — August 23, 2024
CORN EARWORM NUMBERS LOWER
All Fresh Silking Corn Remains on Spray Intervals Prevent Infestation
SITUATION
Pest pressure was lower in most fields this week, as cooler nights and changing weather patterns slowed moth activity. However, counts remain high enough to require regular spray intervals in fields with fresh silks. Harvest continues in full swing as many later varieties have matured earlier than expected due to the hot weather. Early harvested fields are now being plowed down and seeded with cover crops.
European corn borer: Moth captures were very low this week with the exception of sites in Bowdoinham and Dayton, where a small second generation of corn borer may be starting. Both sites were over the spray threshold for moths in silking corn. However, very little larval feeding damage was found in pre-silking corn, and no sites were over threshold.
Corn earworm: All of our sites are on a spray interval for fresh silking corn to prevent infestation. However, moth numbers were down considerably over last week, and many sites can now use a longer spray interval. A 6-day spray interval for silking corn was recommended in Biddeford, Cape Elizabeth, Farmington, Monmouth, Oxford and one Wells site; a 5-day spray interval was recommended in Corinth, Palmyra and one Wells site; a 4-day spray interval was recommended for Auburn, Bowdoinham, Dayton, Gray, and Lewiston.
Fall armyworm: Moth counts in pheromone traps were variable this week. Auburn, Bowdoinham, Cape Elizabeth, Dayton, Gray, Monmouth, Oxford, Wayne 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 light in most pre-silking corn, and many sites have no pre-silking corn remaining. Bowdoinham and Gray were over threshold of 12-15% of plants with fresh injury.
Western Bean Cutworm: Captures of moths in pheromone traps were very low at all locations this week, with most sites catching none, and range from zero to 6. Sprays for corn earworm and 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.
Corn leaf aphids: We are seeing many fields infested with these small, soft-bodied insects. Colonies of bluish-green aphids can cover tassels, stalks and husks. Their waste encourages the growth of the sooty mold fungus, which can cover the husks. If sprays for corn earworm (often FRAC Group 3A) are not providing control of aphids, you may want to try a product with a different chemistry such as Assail® or Sivanto®.
Corn rust: This fungus disease has been seen in several fields this week. It appears as reddish-brown pustules on corn leaves and husks, reducing the quality of the ears. A fungicide spray for rust is only recommended when the symptoms are seen prior to tasseling. Later infections are unlikely to cause enough damage to warrant control measures.
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 | 16 | 0 | 4 | 0 | 4-day spray interval for silking corn | |
| Biddeford | 2 | 0 | 1 | 0 | 10% | 6-day spray interval for silking corn |
| Bowdoinham | 24 | 7 | 4 | 1 | 27% | 4-day spray interval for silking corn |
| Cape Elizabeth | 3 | 0 | 14 | 0 | 6-day spray interval for silking corn | |
| Corinth | 4 | 1 | 0 | 2% | 5-day spray interval for silking corn | |
| Dayton | 21 | 8 | 42 | 1 | 4% | 4-day spray interval for silking corn |
| Farmington | 2 | 0 | 0 | 0 | 6-day spray interval for silking corn | |
| Gray | 16 | 0 | 3 | 4 | 12% | 4-day spray interval for silking corn |
| Lewiston | 32 | 1 | 1 | 0 | 4-day spray interval for silking corn | |
| Monmouth | 3 | 0 | 8 | 0 | 6-day spray interval for silking corn | |
| Oxford | 2 | 0 | 3 | 0 | 6-day spray interval for silking corn | |
| Palmyra | 4 | 0 | 1 | 5-day spray interval for silking corn | ||
| Wayne | 6 | 0 | 0 | 0 | 5-day spray interval for silking corn | |
| Wells I | 2 | 0 | 1 | 0 | 6-day spray interval for silking corn | |
| Wells II | 6 | 0 | 14 | 0 | 5-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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