Sweet Corn IPM Newsletter No. 7 – August 26, 2019

Sweet Corn

Sweet Corn IPM Newsletter No. 7 – August 26, 2019
Click on photos to enlarge.

CORN EARWORM PRESSURE REMAINS HIGH

Moth Activity Down Slightly, But Still a Threat to Silking Corn 

SITUATION
Recent very warm days and nights have pushed maturity of later planted corn. Showers have kept most fields from experiencing drought stress, so overall quality continues to be good. The weather has also allowed insect pressure to remain high. Silking corn is especially at risk due to high numbers of corn earworm throughout the state.

European corn borer:  Moth activity remains low with only one farm in Garland over the five moth per week threshold for silking corn. Most locations caught no moths. Feeding injury by larvae on pre-tassel corn was also low, with no fields exceeding the 15% control threshold.

Corn earworm:  Moth captures decreased slightly or remained stable at most locations this week, but populations are still high enough to threaten any fresh silking corn. A six-day spray interval for silking corn was recommended in Palmyra this week. A five-day spray interval was recommended for silking fields in Levant, Monmouth and Nobleboro. A four-day spray schedule was recommended in Auburn, Biddeford, Bowdoinham, Cape Elizabeth, Charleston, Dayton, Garland, Lewiston, Poland Spring, Sabattus, Wayne and one Wells site.

Western bean cutworm moth
Western Bean Cutworm moth; photo by Lindsey Ridlon

Fall armyworm:  Moth counts were over the 3-moth threshold for silking corn in Bowdoinham, Cape Elizabeth, Lewiston, Monmouth, Poland Spring, Wayne and one Wells site; but all sites were also under a spray interval for corn earworm, so no additional controls should be needed. Larval feeding damage was over the 15% spray threshold at one Cape Elizabeth site this week.

Western bean cutworm:  Moth counts remain high at nearly all trapping locations this week, exceeding the suggested three moth per week threshold for silking corn. Sprays applied to silking corn for corn earworm should also protect against western bean cutworm. Sprays for western bean cutworm on silking corn were recommended in Oxford and Farmington where corn earworm counts were below threshold.

Squash vine borer:  Moth counts remained low this week. No fields were above the threshold of 5 moths.

Picnic beetles can become a problem during the late summer on silking corn. These beetles are about 1/4-inch long, black with orange spots. They can often be found on stalks and ears that are infested with European corn borer or fall armyworm, feeding on sap at an entry or exit hole. They will also feed on the silks and may work their way into the silk channel. While the damage is usually insignificant, customers dislike finding the insects in their bags. Sprays to control corn earworm should provide control of these beetles if they are found in your field.

Birds:  Blackbirds have been damaging cornfields in recent days. They are especially attracted to fields where corn has been allowed to get over-mature. For information on wildlife problems and management options, you can call the Animal and Plant Health Inspection Service office in Augusta at 1.866.487.3297.

Sincerely,

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                      UMaine Extension Diagnostic
P.O. Box 179                           Research Lab, Pest Mgmt. Unit
52 U.S. Route 202                  17 Godfrey Drive
Monmouth, ME  04259          Orono, ME  04473
207.933.2100                          1.800.287.0279

Sweet Corn IPM Weekly Scouting Summary

Location CEW
Moths
ECB
Moths
FAW
Moths
WBC
Moths
Feeding
Damage
Recommendations / Comments
Auburn 14 0 0 12 4-day spray interval for all silking corn
Biddeford 25 0 1 5 0% 4-day spray interval for silking corn
Bowdoinham 9 0 6 11 14% 4-day spray interval for all silking corn
Cape Elizabeth I 20 1 5 6 30% 4-day spray interval for silking corn
Cape Elizabeth II 33 3 0 9 4-day spray interval for silking corn
Charleston 10 3 0 0% 4-day spray interval for all silking corn
Dayton I 72 0 1 31 4-day spray interval for silking corn
Dayton II 67 1 1 22 1% 4-day spray interval for silking corn
Farmington 1 1 0 30 1 spray for WBC on silking corn,
Garland 11 5 0 4-day spray interval for all silking corn
Lewiston 41 1 5 18 4-day spray interval for all silking corn
Levant 4 0 0 5-day spray interval for all silking corn
Monmouth 5 0 4 11 5-day spray interval for all silking corn
Nobleboro 4 0 0 66 7% 5-day spray interval for all silking corn
Oxford 0 0 1 30 0% 1 spray for WBC on silking corn,
Palmyra 2 0 0 6-day spray interval for all silking corn
Poland Spring 11 0 2 67 4-day spray interval for all silking corn
Sabattus 15 0 0 9 4-day spray interval for all silking corn
Wayne 10 0 3 3 12% 4-day spray interval for all silking corn
Wells I 0 0 0 0 No spray recommended
Wells II 25 0 4 8 9% 4-day spray interval for all silking corn

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm
WBC: Western bean cutworm

Corn Earworm Spray Thresholds for Pheromone Traps

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:
UMaine Cooperative Extension Integrated Pest Management
Penn State Pest Watch – Sweet Corn
UMass Amherst Integrated Pest Management

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