Sweet Corn IPM Newsletter No. 4- July 24, 2020
Sweet Corn IPM Newsletter No. 4- July 24, 2020
Click on photos to enlarge.
EARLY CORN HARVEST UNDERWAY
Corn Earworm and Fall Armyworm Numbers Higher in Most Locations
SITUATION:
Corn harvest has started in southern Maine in early planted fields advanced by plastic mulch or rowcovers. Hot weather and timely rain showers have kept corn growing at a rapid pace, so supply should be good in the coming weeks. Corn earworm, fall armyworm and western bean cutworm numbers have been higher in many fields scouted this week, resulting in the first insecticide sprays in some fields and shorter spray intervals in others. Larval feeding damage to young corn remains at low levels this week, so the primary threat at this time is to silking corn.
European corn borer:
Larval feeding injury was not over the 15% control threshold for pre-tassel corn at any of our sites this week. Moths are still flying at many locations, so there is still potential for damage in the near future. Moth counts did not exceed the threshold for silking corn at any location, so no sprays were recommended.
Corn earworm:
Moth captures were higher in some locations this week, increasing the threat at those sites, but other sites have not yet caught any moths. All silking corn should be protected if more than one moth has been caught in traps. A six-day spray interval for silking corn was recommended in: Biddeford, Poland Spring, Sabattus, Wayne, one Lewiston site and one Wells site. A five-day spray interval was recommended for silking fields at Dayton and one Lewiston site. A four-day spray interval was recommended for Cape Elizabeth.
Fall armyworm (FAW):
Moths were generally higher in number this week and were caught at more locations. Moths exceeded the three per week threshold for silking corn in: Cape Elizabeth, Oxford, Poland Spring and one Lewiston site. Only the Poland Spring site was not presently under a spray interval for corn earworm, and required an additional spray for FAW. Larval feeding damage on younger corn did not exceed the threshold anywhere this week, but we expect to see more soon.
Squash vine borer moths were caught in pheromone traps in Biddeford (1), Oxford (14), and Wells (12) this week. Where counts were over the threshold of five moths per week, sprays to protect summer and winter squash, and pumpkins were recommended.
Spotted wing drosophila:
The number of flies caught in traps are increasing this week, raising the threat level to any ripening berries. We are now recommending a 7-day spray interval for fields with ripe raspberries, blackberries and blueberries. For more information visit our website:
Western Bean Cutworm:
We’ve caught this “new” pest at several locations this week. The larvae of western bean cutworms feed on corn plants and move into the ears through the silk channels or the husks. The threshold for feeding injury on plants is 8%. Sprays for corn earworm should protect silking corn from western bean cutworm as well. The optimal time for controlling the larvae is late pre-tassel to tassel, when they move from the leaves and stalk into the ears.
Sincerely,
David T. Handley
Vegetable and Small Fruit Specialist
Highmoor Farm Pest Mgmt. Unit
P.O. Box 179 17 Godfrey Drive
52 U.S. Route 202 Orono, ME 04473
Monmouth, ME 04259 1.800.287.0279
207.933.2100
| Location | CEW
Moths |
ECB
Moths |
FAW
Moths |
%Feeding
Damage |
Recommendations / Comments |
|---|---|---|---|---|---|
| Biddeford | 2 | 1 | 0 | 10% | 6-day spray interval for all silking corn |
| Bowdoinham | 0 | 0 | 0 | 7% | No spray recommended |
| Cape Elizabeth I | 14 | 0 | 0 | 0% | 4-day spray interval for all silking corn |
| Cape Elizabeth II | 15 | 0 | 8 | 3% | 4-day spray interval for all silking corn |
| Charleston | 0 | 4 | 1 | 0% | No spray recommended |
| Corinth | 0 | 1 | 0 | 0% | No spray recommended |
| Dayton | 5 | 0 | 2 | 0% | 5-day spray interval for all silking corn |
| Farmington | 0 | 0 | 1 | 0% | No spray recommended |
| Lewiston I | 7 | 0 | 1 | 5-day spray interval for all silking corn | |
| Lewiston II | 3 | 0 | 7 | 6-day spray interval for all silking corn | |
| Monmouth | 2 | 1 | 2 | 0% | 6-day spray interval for silking corn |
| New Gloucester | 1 | 0 | 3 | 0% | One spray for FAW on silking corn |
| Oxford | 0 | 0 | 6 | 0% | One spray for FAW on silking corn |
| Palmyra | 0 | 4 | 0 | 1% | No spray recommended |
| Poland Spring | 3 | 0 | 7 | 3% | 6-day spray interval for silking corn |
| Sabattus | 2 | 1 | 2 | 0% | 6-day spray interval for silking corn |
| Wayne | 2 | 1 | 1 | 0% | 6-day spray interval for silking corn |
| Wells I | 1 | 0 | 1 | 0% | No spray recommended |
| Wells II | 3 | 1 | 1 | 0% | 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 the 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:
Cooperative Extension Pest Management
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