In this issue:

ECB and CEW Moth Flight Update

Comprehensive Review of Carbaryl (Sevin) Completed

Daily Crop "ET's" at their Peak

Use of Mosquito Trapping Devices on the Homefront

Corn Borer and Corn Earworm Alert: Be Ready for Late-July to Mid-August Flights (Southern MN and WI)

Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul

ECB flights remain low this week, but the 2nd generation emergence should be starting any day (see Figures, below). In addition to 2nd generation ECB, growers should also begin watch for the Corn earworm (CEW). The good news is that moth flights have remained low for most of southern Minnesota thus far this year. The bad news is that CEW flights, migrating from southern corn and cotton producing states, should start increasing during the next 2 weeks. In recent years, we have seen the first increase in moth flights occurring near Blue Earth, then Owatonna, then the Twin Cities, and eventually, all the way to Crookston and North Central Minnesota.

All sweet corn growers and processors in the southern Minnesota and Wisconsin, particularly those with fresh silking sweet corn should be aware of this flight, and consider the thresholds summarized below. Currently, CEW moth catches, in the Twin Cities area (e.g., Rosemount; Dakota Co.), still remain light at 1-2/night. However, all growers in the Twin Cities area, and north, should be aware that moths could be on the way to your area. If you do not have access to a pheromone trap, you can follow key MN sites at the following VegEdge site: http://vegedge.umn.edu/2003/moth.htm. At this site, you can also review the moth flight data for 2002.

Trap notes: If you are cooperating with our pheromone trap network this year, now is the time to get your trap out; place it near early silking corn. Although black light traps are much less sensitive than pheromone traps for CEW, data from light traps can still be useful in that 2-3 CEW moths/night also reflects a significant flight.

Recommended Action Thresholds for CEW control in Sweet Corn:

Sweet corn is most attractive to CEW Moths during the late tassel, EARLY silking stage. CEW prefer to lay most of their eggs on fresh silks; as silks begin to turn brown, and as ears mature, moths will move to nearby sweet corn that is just beginning to silk. CEW will also lay eggs in snap bean, tomato and pepper fields, but sweet corn is probably the preferred host, when given a choice.

Given the damage potential for CEW in sweet corn, action thresholds are very low. For both fresh and processing sweet corn, insecticide sprays should begin when 4% of the plants have eggs or young larvae present on the silks. Unlike ECB, CEW eggs are laid singly, and easy to see if you are relatively young, or not yet using reading glasses. Because it is difficult to search for CEW eggs, many growers use the following trap-based, moth-catch thresholds. The following thresholds have been adapted from Ohio State and Cornell University recommendations.

Spray Schedule for CEW, based on Number of CEW Moths Caught/Week in Pheromone Traps (Scentry; White Nylon Mesh; Heliothis model)

*Refers to maximum daily air (field) temperature.
Note: Spray program should stop once silks are 90% brown; brown silks are less attractive for new egg-lay.

Insecticide Choice, Selection, Notes:

CEW is more difficult to control than the European corn borer (ECB), and not all of the labeled insecticides, or pyrethroids, work as well on CEW. The following pyrethroids are generally effective against CEW. Additional considerations will include Pre-harvest interval (PHI), Re-entry interval (REI) and cost. For a summary of insecticide efficacy data for ECB and CEW, see the July 20, 2001 issue of the MN Veg IPM Newsletter at http://www.vegedge.umn.edu/mnvegnew/vol3/vol3n9.htm.

Notes: The pre-harvest interval (PHI) is not a problem for any product. However, the re-entry (REI) should be considered. All pyrethroids (Asana, Ambush, Baythroid, Capture, Pounce, Warrior, Mustang) and Lannate are Restricted Use Pesticides (RUP). Sevin (carbaryl), SpinTor and Bt products are the few non-RUPs labeled for sweet corn. SpinTor and Bt provide good control of ECB, but less consistent control of CEW.

Lannate is a good ovicidal material, but has very poor residual activity, or action on larvae; must be applied every 2 days, even with relatively light ECB or CEW pressure; not recommended.

Asana is good for CEW control; however, Asana does not provide consistent ECB control.

Overall, Warrior, Baythroid and Capture provide the most consistent level of CEW and ECB control; however, timing of the first spray, at first silk, is most critical for control of all products. Ambush and Pounce will also provide good ECB control, but less consistent CEW control.

**Also note the MAXIMUM product/acre/field that can be applied per year. Read labels carefully.

**For more information: Refer to the 2003 Midwest Vegetable Guide at: http://www.entm.purdue.edu/entomology/ext/targets/ID/index.htm

Bt Sweet Corn: If fresh-market growers are using Bt Sweet Corn (e.g., Rogers/Syngenta hybrids), they should see about 90% control of CEW (as well as 99-100% control of ECB), without any insecticide applications. Sprays for CEW control will only be needed if moth flights remain heavy throughout the year. If needed for CEW, Bt sweet corn would only need to be treated once, e.g., anytime between 20-25% silk. One spray at early to mid silk may also be necessary to control corn rootworm beetles feeding (clipping) on fresh silks. Both northern and western corn rootworm beetles are usually controlled in non-Bt sweet corn with conventional insecticide sprays. Bt sweet corn (current Bt events) will not control adult corn rootworm beetles.

Organic growers: Although some parasitic wasps can be used for ECB control, parasitic wasps are less effective on CEW. The best cost-effective options are to use a Bt product (Bacillus thuringiensis), such as Dipel, and/or an organic-certified pyrethrum product (again, starting at first silk). Check with your organic-certification group regarding which Bt and pyrethrum products are certified organic. Dipel, alone, will often provide effective ECB control. However, for CEW, I would consider a pyrethrum product. Pyrethrum products typically have less residual activity than synthetic pyrethroids, and must also be applied on a 3-5 day schedule, depending on max. field temperatures. *See also new federal organic certification information in: August 23, 2002 newsletter

For related articles on CEW control in sweet corn, please refer to previous issues at the Newsletter site, and type corn earworm in the Search box, at: http://www.vegedge.umn.edu/mnvegnew/mnindex.htm

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
Production Editor: Suzanne Wold, Research Fellow, Department of Entomology, 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 July 23, 2003.
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