Sweet Corn IPM Newsletter No. 4 – July 8, 2010
July 8th, 2010
For full page print version, please see link at the bottom.
Fall Armyworm Moth Counts Up in Some Fields
Corn Earworm, European Corn Borer Remain at Moderate Levels
SITUATION
We are seeing drying silks in some early cornfields this week, meaning that first harvest is not far away! Recent hot weather has sped up corn growth in most fields, although it is getting dry on some sandy soils and a bit of drought stress is becoming visible where plants have not been irrigated.
Corn with Drought Stress, photo by David Handley
European corn borer: Moth counts are generally low again this week. Only one relatively large capture in Dresden exceeded the threshold of five moths for silking corn, so a single spray was recommended. Larval feeding injury exceeded the control threshold of 15% of plants in the pre-tassel to silk stage, showing injury in North Berwick and Wells. Once the corn begins to silk, sprays for European corn borer should be directed at the ears to catch the larvae as they migrate there from the tassels and stalks.
European Corn Borer Larvae on Ear, photo by David Handley
Corn earworm: Pheromone trap catches continue to be low in most locations this week, with the higher counts generally occurring in coastal areas. This week a five-day spray schedule was recommended at one site in Dayton and in Warren. A six-day spray schedule was recommended for silking corn fields in Cape Elizabeth, Lewiston, Monmouth, Poland Spring, Readfield and Wells; but these are not high enough to warrant a spray.
Corn Earworm Moth, photo by David Handley
Fall armyworm: Moth captures of fall armyworm were up significantly in several locations this week, although this does not appear to be a widespread influx of this pest at this time.
Fall Armyworm Eggs on Corn, photo by David Handley
Fall Armyworm Injury on Corn Leaves, photo by David Handley
Fall armyworm moths tend to lay their eggs on the youngest corn available. When the larvae hatch, they chew large, ragged holes in the leaves, and may bore into developing ears. This damage is scouted for, along with European corn borer injury, and a spray would be recommended if the injury exceeded 15% of plants in a pre-silking field. Larvae may also move into the ears through the silk channel, behaving similarly to corn earworm.
Fall Armyworm on Silk, photo by David Handley
Pheromone trap catches of 3 or more moths per week indicate a spray is needed to protect silking corn, unless it is already under a spray schedule for corn earworm. While we have still not caught moths at most locations, fields in Biddeford, Cape Elizabeth, New Gloucester and Poland Spring were over the spray threshold of three or more moths caught per week for silking corn. The New Gloucester field was already on a 6-day spray interval for corn earworm, so no additional sprays should be needed. A single spray on silking corn was recommended at all of the other sites.
Aphids: Be on the lookout for infestations of aphids developing on the tassels, silks and husks. Aphid feeding is not usually a significant problem. However, black sooty mold often develops on the husks as a result of the waste (called honeydew) aphids deposit, and can render the ears unmarketable.
Aphids on Corn Ear, photo by David Handley
Insecticide sprays, other than the Bt’s or spinosad products, that are used to control the major corn pests also offer control of aphids as well, including Asana®, Capture®, Warrior® and Lannate®.
Sincerely,
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management Office
P.O. Box 179 491 College Ave
Monmouth, ME 04259 Orono, ME 04473
(207) 933-2100 1-800-287-0279
| Location | CEWMoths | ECBMoths | FAWMoths | %ECB Damage | Recommendations / Comments |
| Biddeford | 0 | 1 | 4 | 13% | One spray recommended for FAW on all silking corn |
| Cape Elizabeth I | 0 | 0 | 6 | 3% | One spray recommended for FAW on all silking corn |
| Cape Elizabeth II | 1 | 0 | 0 | 0% | No spray recommended |
| Charleston | 0 | 4 | 0 | 1% | No spray recommended |
| Corinth | 0 | 2 | 0 | 0% | No spray recommended |
| Dayton I | 1 | 3 | 2 | 3% | No spray recommended |
| Dayton II | 6 | 0 | 0 | 0% | 5-day spray interval recommended for all silking corn |
| Dresden | 0 | 10 | 0 | 5% | One spray recommended for ECB on all silking corn |
| Farmington | 0 | 1 | 0 | 0% | No spray recommended |
| Jefferson | 0 | 1 | 2 | 0% | No spray recommended |
| Levant | 0 | 2 | 0 | 0% | No spray recommended |
| Lewiston I | 1 | 0 | 0 | 0% | No spray recommended |
| Lewiston II | 0 | 0 | 0 | 0% | No spray recommended |
| Livermore | 0 | 0 | 0 | 1% | No spray recommended |
| Monmouth | 1 | 0 | 1 | 0% | No spray recommended |
| New Gloucester | 2 | 0 | 7 | 0% | 6-day spray interval recommended for all silking corn |
| Nobleboro | 2 | 2 | 1 | 3% | 6-day spray interval recommended for all silking corn |
| North Berwick | 0 | 1 | 0 | 15% | One spray recommended for ECB |
| Oxford | 0 | 0 | 0 | 3% | No spray recommended |
| Palmyra | 0 | 2 | 0 | 0% | No spray recommended |
| Poland Spring | 1 | 1 | 3 | 1% | One spray recommended for FAW on all silking corn |
| Readfield | 1 | 0 | 0 | 0% | No spray recommended |
| Sabattus | 2 | 3 | 0 | 2% | 6-day spray interval recommended for all silking corn |
| Wales | 0 | 0 | 1 | 0% | No spray recommended |
| Warren | 4 | 0 | 0 | 3% | 5-day spray interval recommended for all silking corn |
| Wells I | 0 | 1 | 0 | 22% | One spray recommended for ECB |
| Wells II | 1 | 1 | 0 | 3% | 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. |
| 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. |
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.
| 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. |
Tags: corn, Highmoor Farm, pest management, sweet corn
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