Sweet Corn IPM Newsletter No. 1 – June 27, 2014
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2014 SWEET CORN PEST SEASON BEGINS!
European Corn Borer Moths Active, Larvae Feeding in Early Corn
The 2014 University of Maine Cooperative Extension Integrated Pest Management (IPM) program for sweet corn is underway. More than twenty volunteer farms are serving as pest monitoring and demonstration sites, with fields in North Berwick, Wells, Dayton, Cape Elizabeth, New Gloucester, Poland Spring, Auburn, Lewiston, Sabattus, Nobleboro, Warren, Monmouth, Wales, Wayne, Oxford, Farmington, Levant, Stillwater, Garland and East Corinth. Pheromone traps have been set up at these farms to monitor the adult (moth) stages of European corn borer, corn earworm and fall armyworm, and we have begun scouting the fields for feeding injury by insect larvae. The information collected at these sites along with management recommendations will be shared every week during the season through this newsletter and blog. If you would prefer to receive this newsletter via e-mail, give us a call at 207.933.2100 or send an e-mail message to: firstname.lastname@example.org.
Farmers with well-drained fields were able to get some early plantings going in spite of a rather cool, wet start to the season. Early seedings started under clear plastic or fabric row covers are now in the pre-tassel to tassel stage, with one southern field already starting to show some silk. In spite of the wet conditions during the spring, some fields are starting to get a bit dry, so the recent rain was quite welcome. Warmer weather predicted for next week should speed up plant development. European corn borer moths have been active in some fields, as evidenced by some light feeding damage we have seen in some pre-tassel fields this week.
European corn borer: We have set up pheromone traps for European corn borer this week, and we’ll start reporting on moth activity in the next issue. We found some feeding injury and very small larvae in pre-tassel fields this week, indicating that moths are now laying eggs on the undersides of corn leaves. The egg masses are small and look like overlapping fish scales. European corn borer overwinters in Maine, and is usually the first pest to become a significant problem. To monitor corn borer, we scout 100 corn plants in each field, examining twenty plants in a row at five different locations. This provides a good estimate of the total amount of injury in a field.
In the early stages, European corn borer feeding damage looks like small “pinholes” in the leaves. Whorl stage corn only needs to be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15% because larvae feeding on the later stages are more likely to move into the ears. On the tassels, feeding damage first appears as chewing and brown waste found in the small florets. After the tassel has emerged from the stalk, the larvae chew into the stalk just below it, often causing the tassel to fall over. Sprays during the pre-tassel stage, when both moths and larvae are present, reduce the opportunity for larvae to move into the stalks and ears of the plant. Once the larvae are in the stalks they are protected from sprays. Good spray coverage of the entire plant provides the most effective kill of larvae as they move from one part of the plant to another. Rotating the type of insecticide used also improves control. Materials registered for controlling European corn borer include Bacillus thuringiensis products (XenTari®, Dipel DF®), Avaunt®, Coragen®, Warrior®, Lannate®, Baythroid®, Asana®, Radiant®, Delta Gold®, Mustang®, Sevin XLR® and Larvin®. We found corn borer feeding injury in pre-tassel fields in Sabattus, Farmington, Livermore Falls, New Gloucester and Nobleboro this week; but only the field in Nobleboro exceeded the injury threshold. Once corn reaches the silk stage, sprays may be based on the number of corn borer moths caught in pheromone traps rather than feeding injury. European corn borer moths will lay eggs on flag leaves of silking corn, and the larvae can move into the ears without leaving visible feeding injury that would be noticed when scouting. If more than five moths are caught during a week in a field with silking corn, a spray is recommended. Varieties of corn genetically modified to produce the Bt toxin (e.g. Bt corn, Attribute® varieties), should not need to be sprayed to control European corn borer.
Corn earworm: Pheromone traps are now set up around the state to monitor the arrival of corn earworm. Corn earworm generally appears in Maine in early July, but the actual date varies greatly. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths start being caught at a site, all silking corn in the fields should be protected with a spray. These moths lay eggs on the fresh silks and the larvae move directly into the ears of corn. When corn earworm moths cannot find silking corn to deposit their eggs on, they may lay eggs on the leaves of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm, until the ears become available. When larvae are found feeding on younger corn, the damage is accounted for, along with any borer or armyworm damage, to determine if a spray is warranted.
Fall armyworm: This is usually the last serious corn insect pest to arrive in Maine. The moths must fly in from southern over-wintering sites, and 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. Larvae may also move into the ears through the silk channel, behaving similarly to corn earworm. Pheromone trap catches will indicate if there is a threat to silking corn. However, corn will usually be on a spray program for corn earworm when fall armyworm is present, and both insects would be controlled.
Do-It-Yourself IPM: To get the most accurate information about the pest situation on your farm you should monitor the fields yourself on a regular basis. Pheromone traps and lures are available that can give you an accurate, early warning of the arrival of all of the major insect pests. Traps and lures can be purchased from pest management supply companies such as Gempler’s (1.800.382.8473) or Great Lakes IPM (517.268.5693).
To learn more about IPM scouting techniques, insect identification and control thresholds, order the fact sheet Managing Insect Pests of Sweet Corn available from the University of Maine Cooperative Extension. Color pictures are provided to help with insect identification, and a chart with spray thresholds is supplied to post near your sprayer for easy reference. You can download a copy from the UMaine IPM website or call the Pest Management Office at 1.800.287.0279.
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
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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.