Skip Navigation

Sweet Corn IPM Newsletter No. 6 – August 3, 2018

Print Friendly

Sweet CornSweet Corn IPM Newsletter No. 6 – August 3, 2018
Click on photos to enlarge.

CORN EARWORM THREATENS ALL SILKING CORN

Most Sites Now Have Significant Moth Populations in Silking Corn

SITUATION
As predicted, the warm weather from the south has brought an increase in insect activity, as we come into the peak of the sweet corn season. Growers should be monitoring their fields regularly and be prepared to protect silking corn from the threat of earworm and corn borer. Fall armyworm is likely to become more of a threat in the coming days.

European corn borer:  Activity in pheromone traps increased in most fields this week, although it has not yet led to a noticeable increase in feeding damage. This will likely follow soon however, as the eggs these moths are laying begin to hatch. When more than 5 moths are caught in a trap in a week, a spray is recommended for all silking corn to prevent larvae from entering the ears directly after hatching. Moths exceeded this threshold in Bowdoinham, Garland, Lewiston, New Gloucester, Oxford and Wells. However, all of these sites, except the one Wells field, were also under a spray interval for corn earworm, which should also protect against corn borer. Feeding damage in the field was very light, with no sites over the 15% spray threshold for pre-tassel to silking corn; but this is likely to increase soon.

European Corn Borer Larva

European Corn Borer Larva, photo by David Handley

Corn Earworm Feeding on Corn

Corn Earworm Feeding on Corn, photo by David Handley

Corn earworm:  Numbers of moths caught in traps increased significantly at nearly all sites monitored this week, leading to sprays recommended for corn in most silking fields. A 6-day spray interval for all silking corn was recommended for our sites in Bowdoinham, one Lewiston site, North Berwick, and Oxford. A 5-day spray interval was recommended for one Cape Elizabeth site, Dayton, Garland, one Lewiston site, Nobleboro, Poland, Sabattus and Wayne. A 4-day spray interval was recommended for silking fields in Biddeford, one Cape Elizabeth site, one Dayton site, Levant, New Gloucester, and one Wells site. At this point, it is likely corn earworm pressure will continue and growers should be prepared to protect all silking corn.

Fall armyworm:  No moths were caught in our pheromone traps this week, but we anticipate we will be seeing them soon because we are finding some larval feeding. None of the injury was over the 15% spray threshold.

Squash vine borer:  Moths were over the 5 moth per week threshold in Oxford. All other sites had either one or no moths this week.

Spotted wing drosophila:  Fly counts have been variable this week, with some locations seeing increases (Limington, Readfield) while most locations still had very few, if any flies. The recent heat and rain will improve conditions for spotted wing drosophila (SWD), because they likely increased the amount of rotten fruit in the field and the level of moisture. Both are conducive to fly presence and reproduction. Try keep the planting as free from rotten fruit as possible, remove excess vegetative growth, especially near the base of the plants, and apply a suitable insecticide when flies are observed or larvae are found in the fruit. For more information visit our SWD blog.

Male Spotted Wing Drosophila

Male Spotted Wing Drosophila, photo by Griffin Dill. Actual size: 2-3 mm.

Sincerely,

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                      Pest Management Office
P.O. Box 179                             491 College Avenue
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
%Feeding
Damage
Recommendations / Comments
Biddeford 8 1 0 0% 4-day spray interval recommended on all silking corn
Bowdoinham 2 16 0 0% 6-day spray interval recommended on all silking corn
Cape Elizabeth I 4 0 0 0% 5-day spray interval recommended on all silking corn
Cape Elizabeth II 24 1 0 4% 4-day spray interval recommended on all silking corn
Charleston 0 2 0 0% No spray recommended
Dayton I 4 0 0 0% 5-day spray interval recommended on all silking corn
Dayton II 8 3 0 2% 4-day spray interval recommended on all silking corn
Farmington 0 2 0 0% No spray recommended
Garland 4 5 0 5-day spray interval recommended on all silking corn
Levant 33 0 0 1% 4-day spray interval recommended on all silking corn
Lewiston I 2 5 0 0% 6-day spray interval recommended on all silking corn
Lewiston II 5 3 0 0% 5-day spray interval recommended on all silking corn
New Gloucester 12 5 0 0% 4-day spray interval recommended on all silking corn
Nobleboro 6 3 5-day spray interval recommended on all silking corn
No. Berwick 3 2 0 1% 6-day spray interval recommended on all silking corn
Oxford 2 15 0 0% 6-day spray interval recommended on all silking corn
Palmyra 0 3 0 0% No spray recommended
Poland 5 0 0 5-day spray interval recommended on all silking corn
Sabattus 6 2 0 5-day spray interval recommended on all silking corn
Wales 1 1 0 0% No spray recommended
Wayne 4 0 0 0% 5-day spray interval recommended on all silking corn
Wells I 0 28 0 1% One spray for ECB on all silking corn
Wells II 14 2 0 0% 4-day spray interval recommended on all silking corn

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

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
UMass Amherst Integrated Pest Management

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

 

Tags: , , ,

Comments are closed.