Sweet Corn IPM Newsletter No. 2 – July 3, 2014
Click on photos to enlarge.
CORN BORER, CORN EARWORM AND FALL ARMYWORM MOTHS ACTIVE
Silking Corn Needs Protection in Early Fields
Cornfields are developing fast with the onset of warm (very warm) temperatures this week. Several early plantings are now in silk while others are coming into tassel. Any showers that arrive this weekend will be welcomed in early fields where conditions are very dry. All of the major corn pests have arrived and are active in cornfields in much of the state. These are especially a threat to early silking fields, which growers often spray lightly, if at all, assuming the major pests are not yet present in damaging numbers.
European corn borer: Moth catches are spotty around the state this week with about half of the sites now catching moths. A field in Nobleboro was over threshold of 5 moths per week in an early field of silking corn. Another field in Warren was also over the threshold, but does not yet have corn in silk, so no spray was recommended. European corn borer feeding damage was over the 15% threshold in pre-tassel fields in Biddeford, Bowdoinham, New Gloucester, Sabattus, Livermore Falls and Nobleboro.
Corn earworm: We are now finding corn earworm moths in most of our monitoring sites. Numbers are still low, and most fields do not yet have any silking corn that could be threatened by this pest. When more than one corn earworm moth is found at a site, all silking corn in the fields should be protected with a spray. Additional sprays are based on the average number of moths caught per week or per night (see table below). Only one field in Cape Elizabeth had moths over threshold and early silking corn. A 5-day spray interval was recommended at that location, based on a weekly moth catch of 4.
Fall armyworm: Moths have arrived in many of the fields monitored this week, indicating that cornfields will soon start showing feeding damage from larvae. Fall armyworm caterpillars leave large ragged holes in the corn leaves and lots of sawdust-like waste within the whorl and developing tassels. We found two fields showing feeding damage this week. In silking fields, fall armyworm larvae may enter the ears through the silk channel, leaving little visible damage to the plant. For that reason, when more than 3 fall armyworm moths are caught in pheromone traps in a week a spray is recommended for all silking corn in a field. Only one field in Cape Elizabeth was over the threshold for silking corn this week. However, that same field was also on a spray schedule for corn earworm in silking corn, so no additional sprays should be required to control fall armyworm.
Japanese beetles should soon be appearing in southern and mid-state areas. These insects often find their way into cornfields and feed on the silks of developing ears, causing poor tip fill. Sprays for corn earworm (except Bt’s) will often control Japanese beetle as well.
Spotted wing drosophila: The first capture of a spotted wing drosophila in Maine was reported this week from a wild blueberry field in Blue Hill. These small fruit flies can cause serious fruit losses in raspberries, blueberries and other soft fruits. The flies will only attack fruit that has begun to ripen, and we don’t expect populations to reach damaging levels for a few weeks. For more information visit our website: http://extension.umaine.edu/highmoor/news-events/.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management Office
P.O. Box 179 491 College Avenue
Monmouth, ME 04259 Orono, ME 04473
Sweet Corn IPM Weekly Scouting Summary
|Recommendations / Comments|
|Biddeford||0||4||2||25%||One spray recommended for ECB on pre-tassel corn|
|Bowdoinham||2||0||0||28%||One spray recommended for ECB on pre-tassel corn|
|Cape Elizabeth I||1||0||0||0%||No spray recommended|
|Cape Elizabeth II||4||0||15||0%||5-day spray interval recommended on all silking corn|
|Dayton||0||0||0||0%||No spray recommended|
|Dayton II||1||0||2||2%||No spray recommended|
|Farmington||0||1||0||3%||No spray recommended|
|Lewiston||4||2||1||1%||No spray recommended (no silking corn)|
|Lewiston II||0||4||1||4%||(no silking corn)|
|Livermore Falls||0||0||0||15%||One spray recommended for ECB on pre-tassel corn|
|Monmouth||0||0||0||0%||No spray recommended|
|New Gloucester||1||0||1||1%||No spray recommended|
|Nobleboro||1||10||0||18%||One spray recommended for ECB on pre-tassel-silk corn|
|No. Berwick||1||0||1||40%||One spray recommended for ECB on pre-tassel corn|
|Oxford||1||1||0||4%||No spray recommended|
|Sabattus||1||0||0||38%||One spray recommended for ECB on pre-tassel corn|
|Wales||0||0||0||8%||No spray recommended|
|Warren||0||24||0||0%||No spray recommended (no silking corn)|
|Wells I||0||0||0||0%||No spray recommended|
|Wells II||0||0||1||0%||No spray recommended|
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.
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.
Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the State of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.