Sweet Corn IPM Newsletter No. 5 – July 14, 2010
July 14th, 2010
For full page print version, please see link at the bottom.
Pest Counts Remain Low
Fall Armyworm Damage Increasing
SITUATION
Early corn is now starting to be harvested in southern Maine. Continued hot weather is causing places without irrigation to show significant drought stress. Insect pressure has generally been low this week, although we are seeing an increase in the amount of feeding damage by fall armyworm larvae.
Corn with Drought Stress, photo by David Handley
European corn borer: Moth counts are generally low again this week. Two single sprays were recommended for exceeding threshold for silking corn in Charleston and Dresden. Palmyra was also over threshold, but already on a spray interval for corn earworm. Larval feeding injury did not exceed threshold in any non-silking fields scouted this week.
European Corn Borer Moth, photo by David Handley
Corn earworm: Pheromone trap catches continue to be low in most locations this week. A five-day spray schedule was recommended only in Farmington. A six-day spray schedule was recommended for silking corn fields in Biddeford, one site in Lewiston, New Gloucester, Nobleboro, North Berwick and Palmyra. Single moths were caught in both Cape Elizabeth sites, one Dayton site, Jefferson, one Lewiston site, Old Town, Poland Spring, and Warren; but these were not significant enough to warrant a spray.
Corn Earworm Moth, photo by David Handley
Harstack Trap, photo by David Handley
Fall armyworm: Moth captures of fall armyworm seem to be increasing steadily, along with feeding injury. When scouting, a spray would be recommended if the injury exceeded 15% of plants in a pre-silking field.
Adult Fall Armyworm, photo by David Handley
Fall Armyworm on Silk, photo by David Handley
Larvae may also move into the ears through the silk channel, behaving similarly to corn earworm. 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. Moths exceeded threshold for silking corn at one site in Cape Elizabeth, one site in Dayton, Dresden, and New Gloucester. 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 to protect silking corn was recommended at all of the other sites. Fall armyworm feeding injury exceeded the 15% threshold for pre-tassel stage corn at one site in Cape Elizabeth, and a single spray was recommended.
Corn rust: Rust is a fungus disease that causes reddish-brown pustules to form on the leaves, stalks and husks, reducing the visual quality of the ears. Severe infections can reduce ear size, especially if they occur prior to tasseling. Typically, corn rust does not become a problem until late in the season, because it cannot overwinter in Maine and must move in from the south. A fungicide spray for rust would only be recommended if the infection were noticed in a field prior to tasseling. Later infections are unlikely to cause enough damage to the crop to justify control measures. Materials available to control corn rust include Bravo®, Quilt® and maneb/mancozeb.
Rust on Corn, photo by David Handley
Other Pests of Note:
Japanese Beetles are plentiful in all areas. These insects often find their way into corn fields and feed on the silks of developing ears.
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 | 3 | 1 | 1 | 10% | 6-day spray interval recommended for all silking corn |
| Cape Elizabeth I | 1 | 1 | 1 | 15% | One spray recommended for FAW |
| Cape Elizabeth II | 1 | 0 | 3 | 12% | One spray recommended for FAW on all silking corn |
| Charleston | 0 | 7 | 0 | 4% | One spray recommended for ECB on all silking corn |
| Corinth | 0 | 0 | 0 | 0% | No spray recommended |
| Dayton I | 1 | 0 | 3 | 3% | One spray recommended for FAW on all silking corn |
| Dayton II | 0 | 0 | 2 | 0% | No spray recommended |
| Dresden | 0 | 11 | 3 | 2% | One spray recommended for ECB +FAW on all silking corn |
| Farmington | 6 | 1 | 1 | 1% | 5-day spray interval recommended for all silking corn |
| Jefferson | 1 | 0 | 2 | 1% | No spray recommended |
| Levant | 0 | 2 | 1 | 1% | No spray recommended |
| Lewiston I | 1 | 0 | 2 | 0% | No spray recommended |
| Lewiston II | 2 | 0 | 1 | 2% | 6-day spray interval recommended for all silking corn |
| Livermore | 0 | 3 | 0 | 2% | No spray recommended |
| Monmouth | 0 | 0 | 1 | 0% | No spray recommended |
| New Gloucester | 2 | 0 | 5 | 5% | 6-day spray interval recommended for all silking corn |
| Nobleboro | 2 | 2 | 0 | 0% | 6-day spray interval recommended for all silking corn |
| North Berwick | 2 | 1 | 1 | 7% | 6-day spray interval recommended for all silking corn |
| Old Town | 1 | 4 | 0 | 0% | No spray recommended |
| Oxford | 0 | 0 | 1 | 12% | No spray recommended |
| Palmyra | 2 | 5 | 1 | 2% | 6-day spray interval recommended for all silking corn |
| Poland Spring | 1 | 1 | 0 | 10% | No spray recommended |
| Readfield | 0 | 0 | 0 | 2% | No spray recommended |
| Sabattus | 0 | 1 | 0 | 3% | No spray recommended |
| Wales | 0 | 0 | 0 | 0% | No spray recommended |
| Warren | 1 | 0 | 0 | 4% | No spray recommended |
| Wells I | 0 | 0 | 1 | 3% | No spray recommended |
| Wells II | 0 | 2 | 0 | 8% | 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. |
Tags: corn, Highmoor Farm, pest management, sweet corn
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