Sweet Corn IPM Newsletter No. 6 — July 19, 2024
CORN EARWORM, FALL ARMYWORM NUMBERS RISE
Silking Corn Requires Protection
SITUATION
Early corn harvest is underway in southern Maine. Corn earworm and fall armyworm numbers have increased significantly at most locations. Feeding damage on pre-silking corn from fall armyworm is also increasing. Expect continued warm nights to keep moth activity high in the coming days.
European corn borer: Moth counts were higher this week. Sites in Biddeford, Dayton, Farmington, Lewiston and Wells were over the spray threshold for corn borer in silking corn. Larval feeding damage in late whorl and pre-tassel was under threshold at most sites, but when combined with fall armyworm damage several were over the spray threshold (see Fall Armyworm below) sites in Biddeford, Bowdoinham, Farmington, Oxford, and Wells.
Corn earworm: Moths captures this week were generally higher, indicating tighter spray intervals for most locations. A 6-day spray interval for silking corn was recommended in Bowdoinham, Farmington, Oxford, Wayne and one Wells site; A 5-day spray interval was recommended in Dayton and one Lewiston site; a 4-day spray interval was recommended for Biddeford, Cape Elizabeth, Gray and one Lewiston site.
Fall armyworm: Captures of moths were higher at most locations this week. Sites in Cape Elizabeth, Gray, Lewiston and Wells were over the three-moth threshold for silking corn in pheromone traps, but these fields were under a spray interval for earworm. Larval feeding damage was generally higher on pre-silking corn. This should be combined with any European corn borer injury when found. A threshold of 12-15% of plants with fresh injury is used to determine if a spray should be applied. Combined feeding damage was over the threshold at Biddeford, Cape Elizabeth, Wayne and Wells.
Western Bean Cutworm: Moth numbers were higher in some locations this week, but the distribution remains spotty. Sprays for corn earworm or fall armyworm should protect silking corn from western bean cutworm. The optimal time for controlling the larvae is late pre-tassel to tassel.
Squash vine borer: Moth numbers in pheromone traps are over the control threshold at most locations. Sprays to protect squash plants from egg laying moths were recommended in Lewiston, Farmington, Oxford, Biddeford. See the New England Vegetable Management Guide for control options.
Reminder: University of Maine Highmoor Farm Field Day: Wednesday, July 24. Orchard tours and tree fruit program 1-5 pm; Vegetable and berry tour 5-7 pm. Follow the event’s website for registration information.
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 | %Feeding Damage | Recommendations / Comments |
|---|---|---|---|---|---|
| Biddeford | 10 | 1 | 9 | 15% | 4-day spray interval for silking corn |
| Bowdoinham | 2 | 1 | 0 | 6% | 6-day spray interval for silking corn |
| Cape Elizabeth | 15 | 2 | 21 | 13% | 4-day spray interval for silking corn |
| Dayton | 5 | 6 | 0 | 8% | 5-day spray interval for silking corn |
| Farmington | 1 | 6 | 1 | 10% | 6-day spray interval for silking corn |
| Garland | 3 | 1 | 0 | 0% | 6-day spray interval for silking corn |
| Gray | 21 | 2 | 19 | 2% | 4-day spray interval for silking corn |
| Lewiston | 4 | 4 | 8 | 11% | 5-day spray interval for silking corn |
| Lewiston II | 15 | 5 | 5 | 15% | 4-day spray interval for silking corn |
| Oxford | 3 | 1 | 1 | 8% | 6-day spray interval for silking corn |
| Palmyra | 1 | 3 | 0 | 0% | No spray recommended |
| Wayne | 2 | 3 | 1 | 22% | 6-day spray interval for silking corn |
| Wells I | 3 | 3 | 3 | 7% | 6-day spray interval for silking corn |
| Wells II | 3 | 5 | 21 | 20% | 6-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.
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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