Sweet Corn IPM Newsletter No. 9 – August 11, 2010
August 11th, 2010
For full page print version, please see link at the bottom.
Insect Pressure High in Most Cornfields
Drought Stress Showing in Unirrigated Fields
SITUATION
Warm temperatures have kept corn development at a rapid pace, although many areas are very dry and some unirrigated fields are showing drought stress. Both corn earworm and fall armyworm moth counts remain high this week and weather patterns suggest that insect pressure is likely to remain fairly high in the near future. Tropical storms now forming in the ocean could bring large moth flights to Maine in the weeks ahead, so keep an eye on the weather and keep silking corn protected.
European corn borer: While moth counts remained low at most sites this week, two locations saw moth numbers jump up, suggesting the possible start of a second generation of European corn borer. This might be expected given the very early start to the season this year. Typically, we see only one distinct generation in Maine, but in years where the growing season is longer than normal we may see the start of a second generation, which can threaten late silking corn. Moths were over threshold for silking corn in Nobleboro, North Berwick and Sabattus this week; but all locations are on a spray interval for corn earworm. The larval feeding injury on pre-silking corn was not exceeded at any site this week.
Corn earworm: Pheromone trap catches remain high in most locations this week, including two of the highest counts of the season. Three-day spray intervals for fresh silking corn were recommended for very high moth pressure in Dresden and North Berwick this week. Four-day spray intervals were recommended in Biddeford, Cape Elizabeth, Dayton, Jefferson, Levant, one site in Lewiston, Monmouth, New Gloucester, Nobleboro, Oxford, Palmyra, Poland Spring, Readfield, Sabattus, Wales, Warren, Wayne and Wells. Five-day spray intervals were recommended in Farmington, one site in Lewiston and Old Town. A six-day spray interval was recommended in Charleston.
Corn Earworm Moth, photo by David Handley
Fall armyworm: Moth counts were at their highest levels of the season in many locations this week, suggesting increased pressure from fall armyworm can be expected in the coming days. Moths exceeded threshold for silking corn in Biddeford, Cape Elizabeth, Dayton, Jefferson, Lewiston, Monmouth, New Gloucester, Nobleboro, North Berwick, Poland Spring, Readfield, Warren and Wells. All of these fields were already on a spray interval for corn earworm, so no additional sprays were recommended. Fall armyworm feeding injury exceeded the 15% threshold for pre-silking corn in Biddeford and Jefferson this week.
Male Fall Armyworm Moth, photo by David Handley
When Should You Stop Spraying?
When a silking cornfield is under a recommended spray interval for corn earworm, we usually recommend that spraying be stopped once the silks have become thoroughly dried and brown. At this point, corn earworm moths are unlikely to lay eggs on it. However, if earworm pressure is very high (e.g. 91+ moths per week) and/or fall armyworm moths are over threshold (3+ moths per week), then spraying should probably continue until either the moth counts drop or you reach the required days before harvest (dh) for the product being used.
Airblast Sprayer on Corn, photo by David Handley
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 | CEW Moths |
ECB Moths |
FAW Moths |
%ECB +FAW |
Recommendations / Comments |
| Biddeford | 67 | 2 | 69 | 31% | 4-day spray interval recommended for all silking corn |
| Cape Elizabeth I | 83 | 1 | 44 | 7% | 4-day spray interval recommended for all silking corn |
| Cape Elizabeth II | 80 | 0 | 29 | 2% | 4-day spray interval recommended for all silking corn |
| Charleston | 2 | 0 | 0 | 6-day spray interval recommended for all silking corn | |
| Corinth | 10 | 0 | 1 | 0% | 4-day spray interval recommended for all silking corn |
| Dayton I | 52 | 1 | 21 | 3% | 4-day spray interval recommended for all silking corn |
| Dayton II | 53 | 1 | 12 | 0% | 4-day spray interval recommended for all silking corn |
| Dresden | 135 | 4 | 0 | 0% | 3-day spray interval recommended for all silking corn |
| Farmington | 6 | 2 | 2 | 5-day spray interval recommended for all silking corn | |
| Jefferson | 14 | 0 | 3 | 19% | 4-day spray interval recommended for all silking corn |
| Levant | 8 | 0 | 0 | 2% | 4-day spray interval recommended for all silking corn |
| Lewiston I | 30 | 0 | 10 | 0% | 4-day spray interval recommended for all silking corn |
| Lewiston II | 6 | 2 | 22 | 8% | 5-day spray interval recommended for all silking corn |
| Monmouth | 26 | 0 | 10 | 2% | 4-day spray interval recommended for all silking corn |
| New Gloucester | 31 | 0 | 236 | 0% | 4-day spray interval recommended for all silking corn |
| Nobleboro | 21 | 39 | 13 | 2% | 4-day spray interval recommended for all silking corn |
| North Berwick | 120 | 7 | 7 | 1% | 3-day spray interval recommended for all silking corn |
| Old Town | 4 | 0 | 0 | 5-day spray interval recommended for all silking corn | |
| Oxford | 14 | 2 | 1 | 3% | 4-day spray interval recommended for all silking corn |
| Palmyra | 8 | 0 | 0 | 1% | 4-day spray interval recommended for all silking corn |
| Poland Spring | 36 | 0 | 19 | 8% | 4-day spray interval recommended for all silking corn |
| Readfield | 40 | 5 | 9 | 0% | 4-day spray interval recommended for all silking corn |
| Sabattus | 18 | 24 | 0 | 0% | 4-day spray interval recommended for all silking corn |
| Wales | 18 | 0 | 2 | 0% | 4-day spray interval recommended for all silking corn |
| Warren | 53 | 0 | 4 | 0% | 4-day spray interval recommended for all silking corn |
| Wayne | 11 | 0 | 2 | 0% | 4-day spray interval recommended for all silking corn |
| Wells I | 26 | 0 | 14 | 4% | 4-day spray interval recommended for all silking corn |
| Wells II | 51 | 0 | 21 | 7% | 4-day spray interval recommended for 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. |
| 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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