Sweet Corn IPM Newsletter No. 11 – August 25, 2010
August 25th, 2010 
For full page print version, please see link at the bottom.
Pest Counts Remain High
For Many Fields the End of the Season is in Sight
SITUATION
Moth counts continue to be variable around the state, with relatively high pressure in the southern and coastal regions and lower pressure in the north and western regions. Fall armyworm feeding injury is becoming more prevalent in younger fields not yet being sprayed for corn earworm. However, most fields have little, if any, corn remaining which is not yet in silk. Dryness continues to plague many late fields, which could reduce ear size and quality as we move towards the end of the season.
European corn borer: Moth counts were very low this week, suggesting that what earlier looked to be an emerging second generation of this pest may have fizzled out. No fields were over threshold for moths in silking cornfields, and no significant feeding injury in younger corn was found at any of the sites. Remember that European corn borer overwinters in the corn stalks and stubble left on the field. As soon as fields are harvested it can be helpful to mow and/or plow down all of the plant residue to reduce the overwintering population. Seed a cover crop, such as rye or oats, to reduce soil erosion and conserve soil nutrients and organic matter.
Corn earworm: Pheromone trap catches were lower in most locations this week, but still high enough to require short spray intervals at many sites. A three-day spray interval for silking corn was recommended for very high moth pressure at one site in Cape Elizabeth this week. Four-day spray intervals were recommended in Biddeford, one Cape Elizabeth site, Corinth, Dayton, Dresden, Levant, Lewiston, New Gloucester, Nobleboro, Oxford, Old Town, Poland Spring, Wales, and one site in Wells. Five-day spray intervals were recommended in Charleston, Monmouth, Readfield, Sabattus and a site in Wells. Six-day spray intervals were recommended in Farmington, Jefferson, and Warren. No sprays for corn earworm were necessary for fields in Palmyra and Wayne.
Corn Earworm Moth, photo by David Handley
Harstack Trap, photo by David Handley
Fall armyworm: Similar to corn earworm, moth counts were quite variable around the state this week. Moths exceeded threshold for silking corn in Biddeford, Cape Elizabeth, one site in Dayton, Jefferson, Levant, Lewiston, New Gloucester, Nobleboro, Poland Spring, Readfield and one site in 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 Cape Elizabeth, Dayton, Nobleboro, North Berwick and Poland Spring.
Fall Armyworm Injury on Corn Leaves, photo by David Handley
Corn smut has been found in a field this week. This fungus disease is easily recognized by the large galls which form in the ears, tassels, stalks and leaves. The young galls are silvery-white in color. When the galls mature they rupture into masses of powdery, black spores. This fungus tends to infect plants with a prior injury, perhaps from cultivation or insect feeding. Smut usually affects a few plants in a field and is not considered an economically significant problem. There is no effective fungicide for corn smut.
Smut 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
Sweet Corn IPM Weekly Scouting Summary
| Location | CEWMoths | ECBMoths | FAWMoths | %ECB +FAW |
Recommendations / Comments |
| Biddeford | 25 | 0 | 40 | 6% | 4-day spray interval recommended for all silking corn |
| Cape Elizabeth I | 24 | 0 | 44 | 37% | 4-day spray interval recommended for all silking corn |
| Cape Elizabeth II | 164 | 1 | 53 | 19% | 3-day spray interval recommended for all silking corn |
| Charleston | 4 | 0 | 1 | 5-day spray interval recommended for all silking corn | |
| Corinth | 17 | 1 | 0 | 3% | 4-day spray interval recommended for all silking corn |
| Dayton I | 20 | 1 | 52 | 77% | 4-day spray interval recommended for all silking corn |
| Dayton II | 35 | 0 | 0 | 28% | 4-day spray interval recommended for all silking corn |
| Dresden | 29 | 1 | 1 | 4-day spray interval recommended for all silking corn | |
| Farmington | 2 | 0 | 2 | 6-day spray interval recommended for all silking corn | |
| Jefferson | 2 | 0 | 5 | 6-day spray interval recommended for all silking corn | |
| Levant | 33 | 0 | 0 | 1% | 4-day spray interval recommended for all silking corn |
| Lewiston I | 10 | 0 | 3 | 4-day spray interval recommended for all silking corn | |
| Lewiston II | 66 | 0 | 6 | 4-day spray interval recommended for all silking corn | |
| Monmouth | 5 | 0 | 1 | 0% | 5-day spray interval recommended for all silking corn |
| New Gloucester | 9 | 0 | 111 | 1% | 4-day spray interval recommended for all silking corn |
| Nobleboro | 22 | 0 | 9 | 99% | 4-day spray interval recommended for all silking corn |
| North Berwick | 20 | 0 | 2 | 25% | 4-day spray interval recommended for all silking corn |
| Old Town | 20 | 0 | 0 | 4-day spray interval recommended for all silking corn | |
| Oxford | 8 | 0 | 2 | 4-day spray interval recommended for all silking corn | |
| Palmyra | 1 | 0 | 0 | No spray recommended | |
| Poland Spring | 56 | 0 | 13 | 36% | 4-day spray interval recommended for all silking corn |
| Readfield | 6 | 0 | 3 | 5-day spray interval recommended for all silking corn | |
| Sabattus | 4 | 0 | 2 | 5-day spray interval recommended for all silking corn | |
| Wales | 19 | 0 | 1 | 4-day spray interval recommended for all silking corn | |
| Warren | 3 | 1 | 2 | 6-day spray interval recommended for all silking corn | |
| Wayne | 1 | 0 | 0 | 0% | No spray recommended |
| Wells I | 41 | 0 | 8 | 1% | 4-day spray interval recommended for all silking corn |
| Wells II | 7 | 0 | 1 | 4% | 5-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.
HARVESTING PUMPKINS
Pumpkins and winter squash are maturing early this year, causing a lot of head scratching and wondering what to do with orange pumpkins just in time for Labor Day. If the vines and foliage are in good condition it may be best to leave the fruit in the field. However, early harvest and storage may be preferable to leaving the fruit in the field particularly if the vines are in poor condition. Appropriate application of protectant fungicides such as chlorothalonil prior to harvest will help protect the fruit, stems, and foliage from powdery mildew, black rot and other fruit rots and should increase storage life.
Leaving the pumpkins in the field once foliage cover is reduced or after the vines have died may lead to extensive losses of otherwise marketable fruit. Foliage cover is needed to prevent sunscald of the fruit; and dead, decaying vines can reduce the quality of pumpkin stems. If the field has a history of Fusarium or Phytophtora, leaving mature fruit in the field will increase the likelihood of losses due to fruit rot. If you do plan to store the fruit in the field, cut the fruit from the vine and windrow the fruit in drier sections of the field. Cutting the fruit from the vine will help protect the stem from the spread of powdery mildew along the vine and can reduce shriveling and shrinkage of the stem. It is important to scout for insects feeding on the fruit and stems. The most common and serious pests are squash bug nymphs and adults and the striped cucumber beetle. Insect feeding on the fruit or stems will result in unsightly scarring and pitting which can also allow entry of diseases. Control these insects with appropriate insecticides (consult the latest edition of the New England Vegetable Management Guide for a list of available insecticides).
Ideally, pumpkins should be harvested when fully mature, with a deep orange color and hardened rind. However, as long as pumpkins have started to turn color, they will ripen off the vine if held under the proper conditions. While not ideal, this may be preferable to leaving them in the field if conditions are not favorable. Only bring in injury and disease-free fruit to cure and store. If necessary, pumpkins can be ripened in a well-ventilated barn or greenhouse. The best temperatures for ripening are 80-85°F with a relative humidity of 80-85%. Night temperatures should not drop below the sixties. Even if pumpkins are ripe, a period of curing can improve storage life. The curing period should be about 10 days. During this process, the fruit skin hardens, wounds heal and immature fruit ripens – all of which prolongs the storage life.
Pumpkins should be stored in a cool, dry place. Ideal temperatures are between 50° and 60° F and relative humidity of 50 – 70%. Higher humidity allows condensation on the fruit with risk of disease, and lower humidity can cause dehydration. Higher temperatures increase respiration and can cause weight loss. Store fruit on pallets or in large bins, being careful not to overfill or stack pumpkins too high. Pressure bruises can reduce storage life. Stacking pumpkins on dirt or concrete floors can result in significant fruit losses to fruit rots. Even if it is difficult to provide the ideal conditions, storage in a shady, dry location, with fruit off the ground or the floor, is preferable to leaving fruit out in the field.
Thanks to –R. Hazzard, J. Howell, A. Carter, and Robert Wick. University of Massachusetts; Dale Riggs & Robert Rouse, Pumpkin Production Guide, NRAES; Maurice Ogutu, University of Illinois Extension, in Vegetable Growers News, August 2004; and Liz Maynard, Purdue University; Andy Wyendandt, Wes Kline, Rutgers Univ.
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