Pheromone and Light Traps for Sweet Corn Insects

Bill Hutchison, Ext. Entomologist, University of Minnesota, Rick Weinzierl, Ext. Entomologist, University of Illinois

Corn Earworm -- Although pheromone traps are available for use in monitoring many insect pests of vegetables, their use is particularly important in monitoring flights of corn earworm moths. Because the corn earworm does not overwinter in Minnesota or Wisconsin, its seasonal pattern of occurrence is more dependent on the timing of its immigration into an area than on degree-day accumulations after any specific winter or spring starting date.

The ONLY way to judge the combined effects of immigration timing and local development, to determine the need for insecticide applications in sweet corn, is to use a pheromone trap. Corn earworm traps are large, cone-shaped traps constructed of wire or nylon screening. (Paper sticky traps are not effective for monitoring this pest.)

Click here to see suppliers of traps and lures. Traditional wire-mesh traps can be ordered from Bob Poppe, Lexington, IL (309-723-3201) or from Great Lakes IPM or Gemplers (phone numbers, etc. in the following table). Our experience in Minnesota is that the nylon-mesh traps work well for corn earworm. Most of the other companies sell the nylon mesh traps. ONLY order HERCON pheromone lures (containing the synthetic version of the pheromone that females use to attract males) from Great Lakes IPM or Gemplers. Request a packet of 10 Hercon "Zealure tapes" for each trap you operate. You will need to change the lures in the trap every 7-14 days, depending on temperature (the hotter, the more frequent) and known intensity of moth flights, and you will have the best information if you check the traps every day or at least 5 days/week. Traps tell you when male moths are flying (and mating is ongoing and females are laying eggs); egg hatch usually occurs within 2 to 5 days (depending on temperatures) after moths are caught.

In most Minnesota and Wisconsin locations, and in most years, corn earworm does not become a significant problem until mid- to late-August, when the majority of moths migrate to the upper Midwest. However, in 1999 in Minnesota, we had a significant flight in June, resulting in very heavy infestations (50%+ of ears infested) on early-planted sweet corn.

Beginning in 2000, I am recommending that Minnesota growers place their corn earworm traps out in mid-May to ensure that they track the early flight, as well as the traditional August flight.

Once moths arrive, multiple applications are often needed to protect sequential plantings of sweet corn (during silking). In Illinois, the period extends from early June through late September or early October. In other areas or years, the "earworm season" may be much shorter, perhaps spanning only mid August through mid September. Using pheromone-baited traps allows growers to decide when to spray and when to save the money and effort when sprays are not needed. For more information on earworm management, please refer to last year's newsletter article (August 19, 1999), located at: http://www.vegedge.umn.edu/mnvegnew/vol1/cew0818.htm

European corn borer -- Although pheromone traps can be used for corn borer, several years of research in Minnesota indicates that these traps are not as consistent as light traps, either within the season, or across locations. In Minnesota, we are now relying entirely on light traps for tracking corn borer flights.

Light traps are beneficial for several reasons:

catch female moths as well as males (pheromone only catch males), ·
we have a 30+ year light trap data base, for some locations to compare to, as a benchmark
light traps capture all strains or biotypes of the corn borer (univoltine vs. traditional bivoltine (2-gen./yr strain)
light traps catch other species that can be of importance (e.g., armyworm)

One disadvantage of light traps is that you do need a power source, and yet still have the trap close to a corn field and/or grassy/weedy area. Despite this obstacle, light traps continue to be the most popular monitoring tool for corn borer.

Pheromone traps continue to be preferred for corn earworm because of the reliability of the earworm ph. lures, AND because of relatively LOW sensitivity to light traps. Light traps WILL detect earworm moth flights, but it is common to just pick up 1-2 moths, which can sometimes be missed. Bottom line, is that a light trap really gives too many "false negative" results for earworm. A few moths in a light trap indicate a significant flight is likely taking place; however, because of its low sensitivity, ZERO earworm moths can also mean the moths are here, we are just not detecting them (=false negative error).

Various light-trap networks have been in place for over 30 years in MN and WI, and for some areas of IL. These are maintained by many volunteers (several vegetable processing companies), as well as some employees of the respective Departments of Agriculture. Beginning in 2000, the Midwest Food Processors Assoc. (Madison, Wisc.) will be providing additional funding to help expand the network for both corn borer and corn earworm. This partnership, along with the Minnesota Dept. of Agriculture and Extension personnel, will help to ensure that this network is maintained for years to come.

To make the trap catch data more accessible, the entire system (with error checking included) is web-based. In preparation for the 2000 field season, the web site ("Bug Web") will be expanded. Bug Web is presently located at: http://www.mnipm.umn.edu

Future editions of BugWeb can be accessed from the home (welcome) page of the VegEdge site at: http://www3.extension.umn.edu/ If you have not already done so, type the VegEdge address into your WWW browser, for future use this year.

Light Trap Network Dr. Ken Ostlie, Entomology, University of Minnesota, is the coordinator for the Light Trap Network. As part of the MWFPA grant, there are plans to expand the network in two key ways:

Expand it from MN to also include WI, IL and IA
Expand it from corn borer only, to also include corn earworm (the corn earworm network will be based on pheromone traps, as discussed above)

With multiple processing companies having multiple production sites in all four states, it is imperative to have this information available for the entire region, in a timely manner, and in one place. The expansion of the network will probably require two years to complete. For more information on the network, you can contact Dr. Ostlie at 612-624-9272, or at: kostlie@extension.umn.edu

Final Note: With all complications aside, pheromone traps and light traps provide valuable information on the timing and intensity of corn borer flights. Trap monitoring of both pests is especially important pepper and green bean growers because sampling programs for these crops cannot rely on assessments of foliar feeding to indicate corn borer presence or density.

Bill Hutchison and Eric Burkness will provide more information about corn earworm and European corn borer management in future issues of the newsletter. In the meantime, if you have any questions about traps or lures, please contact Eric Burkness, 612-624-3670 (Hutchison lab), or at: burkn001@tc.umn.edu

Eric can also provide you with a copy of a 2-page handout (by fax or mail), that provides all the background information about the light trap network

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised February 25, 2000.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©1999 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.