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WEB ONLY EDITION

Late-Season Corn Earworm Alert & European Corn Borer Update

Snap bean Alert!

Order: 2007 Minnesota Vegetable Guide

Insect, Pest Fact Sheets
Vol 4   August 3, 2007

Late-Season Corn Earworm Alert & European Corn Borer Update

Bill Hutchison & Eric Burkness, Dept. of Entomology, St. Paul, Minn.

As in previous years, the 2007 Corn Earworm (CEW) flight is now beginning to pick up some momentum.  However, the increase in CEW trap catch is limited to a few locations in the upper midwest, including Blue Earth, MN (IA-MN border), with flights of 93/night (7/27) and 66/night (7/31), and Rosemount, where we are seeing a gradual increase to 10/night.  We have also had the Low-level jet (LLJ) and synoptic weather systems conducive to support migration of CEW moths to Minnesota. According to Mike Sandstrom (NIU), these systems originated in SW Kansas and the panhandle area of NW TX and OK, where moth flights have also been high the past 7-10 days. Interestingly, to date, CEW moth flights have remained low, east of the MN catch area, e.g., into southern WI, northern IL and MI.  It is also useful to compare these early 2007 results with CEW migration timing observed in recent years at Rosemount (UMORE Park, Expt. Station), 2004-2006 (Fig. 1).  

Most state extension recommendations now support the use of pheromone traps for monitoring CEW flights and to assist with making treat, no-treat decisions for silking sweet corn and other attractive late-season crops.  However, there is some variation in the specific “trap-catch action thresholds” that some states provide. In brief, I want to expand on the update we gave last year for Minnesota, but also show the results of the past 3 years of field research (Rosemount), where we have tracked the timing of late-season moth flights in relation to sweet corn silking, and subsequent ear infestations (Fig. 1).  The data support the use of relatively conservative action thresholds of either 5 moths/night for the Hartstack (wire-mesh) traps and approx. 2/night for the Scentry (nylon-mesh) trap.  Moth flight data shown in Fig. 1 is only for Hartstack traps, which provides consistent results for both low and high moth flights; Scentry traps tend to catch only about ½ of the Hartstack catch, and at low level flights, may not catch CEW at all.  Nevertheless, some Scentry traps are still being used, and the lower threshold should work fine in most cases, for these late-season flights. However, because there is some uncertainty with the efficiency of the Scentry trap, we are encouraging increased use of the Hartstack trap, and many more are now in place this year. Also, in some regions, black-light traps may continue to be used for CEW, however, but are also not recommended, due to similar inefficiency for CEW. 
  
CEW graph

PestWatch: To continue to monitor CEW flights this season, please follow the flights being posted, almost daily in some locations, at the new National CEW Map, hosted at Penn State University, "PestWatch".
Thanks again to the many cooperators who make this possible.

IPM and Resistance Management Recommendations for CEW, 2007:
As noted last year (Aug 3, 2006; Vol. 3), we remain concerned about the current and future efficacy of the synthetic pyrethroids for CEW control in sweet corn.  Some of this concern is also related to the challenge of correct timing and frequency of sprays, targeted during the rapid silk phase and ensuring that CEW eggs and larvae receive an effective dose, and/or residual activity is present on the silks during larval hatch. Given the fact that eggs hatch in 3-5 days (typical summer temps.) and larvae only need on average of ca. 45 min., following hatch, to move down the silk channel and enter the ear tip (and thus avoid additional insecticidal mortality), control timing is a challenge, and processors and growers must always be aware of these limitations, plus weather-related interruptions and constraints that all limit the efficacy of foliar applied insecticides.  That said, please consider the following options in managing CEW:

  • Fresh-market growers: If you are using Bt sweet corn (e.g., Attribute Bt; Syngenta Corp.), these hybrids provide very good CEW control (usually 80-90% control; as well as 100% control of ECB). For these growers this is the most effective alternative to pyrethroids; 1 spray, however, may still be needed during silking if Corn Rootworm beetles, or Western Bean cutworm are present.
  • If you are not using Bt sweet corn, and moth counts are >5 moths/night, for 3 consecutive nights, and sweet corn is silking, consider the following options to improve efficacy under high pressure situations:
 
  • The first CEW spray should be applied at peak silk (50% of plants silking), with subsequent sprays at 3-4 day intervals, for a max. of 4-6 sprays, until most silks have turned brown (based on 10+ years of MN data).
  • IF a 1st spray was applied at “row-tassel” (also can = 1st silk), for ECB (which is Good Timing for ECB), then a CEW spray will also be needed at 50% silk. 
  • DO NOT WAIT 5-6 days after the Row-Tassel (ECB) spray, to apply the next spray. That is, if both ECB and CEW are present, and the 1st spray is applied at Row-Tassel, then the 2nd spray will still be required in 3-4 days, or whenever 50% silk is reached.
  • In High-pressure CEW areas (e.g., >25 moths/night), and you are concerned about pyrethroid resistance, consider using the Maximum pyrethroid rate for the 1st and/or 2nd sprays (timing and efficacy of the 1st two sprays is most critical).  For the moderate levels of resistance observed to date, we found in a 2006 trial that the maximum rate for Capture for the 1st two sprays, followed by 2 sprays of Warrior (max rate), provided 100% control (at the silk timings mentioned above).
  • In small plot trials, which also mimic small fresh-market, ground-application spray programs, and with the standard rates for pyrethroids, we have obtained only 40-60% control of CEW, on average, in MN and WI trials since 2000; thus the need for higher pyrethroid rates.
  • Tank-mixes of pyrethroids with Lannate™ will provide an additional 10-20% control; however, previous research indicates this additional control is additive only, with no evidence of a synergistic effect with pyrethroids.
  • The use of spinosad based treatments, including SpinTor™ tank-mixed with pyrethroids, or the organic formulation, Entrust™ (both, Dow AgroSciences), will provide some control of low-moderate infestations, but efficacy data have been inconsistent. For organic growers, Dipel® (Bt foliar product) should still be available; however, multiple applications are necessary, again directed at the silks. Foliar Bt products are sensitive to UV radiation, and lose residual activity within 1-3 days after application. Pyganic™, an organic-certified natural pyrethrum product, is expensive, has low residual persistence, and provides less control than the synthetic pyrethroids.
  • Silk Clipping: Although Rootworm beetles can severely clip silks and reduce pollination, if it occurs early, we have found (3 yrs of research), that mechanical clipping of silks, AFTER POLLINATION, can reduce CEW egg and larval populations, and thus provide an alternative to pyrethroids. Clearly, this will only be practical for Small Fresh-Market and/or Organic plantings, but given the limited alternative options, this should be considered. Growers can try this on their farms, in selected plantings, where you have the on-farm labor to do so.  KEY: Timing of clipping should be 4-5 days After 100% Silk; this should be adequate time for pollination to occur with most hybrids (we have not tested all hybrids). Silks should be clipped down to husk; there will be some silk re-growth, and two clippings may be required. We have on-going research in place to further evaluate this option, and will provide more detailed results as they become available. 
  • Large production fields for processing sweet corn, will gain some benefit from aerial applications, that are likely to kill moths as well as eggs and larvae. The processing industry can also benefit from additional “process-out” methods in processing facilities.
  • Regardless of initial plans, be sure to keep good records of your actual spray dates, silking dates, and final level of control. Comparing this to CEW flight records (for traps on your farm, or regional traps) after the season will allow you to better evaluate what worked well, or not, for a given planting date.

European corn borer: European corn borer (ECB) flights have been very low for most MN locations the past 5 years (with exception of a few central MN univoltine “hot spots”). We are currently experiencing the 2ndgeneration of the bivoltine strain of ECB (as of 8/1, 1931 degree-days, 50F base). Subsequently, we are beginning to see significant increases for several black light traps (BLT) in the state. Specifically, one black light trap near Owatonna, MN, where over 400 moths were collected in one night (confirmed 8/2).  The ECB moth flight has also picked up at Rosemount (69/night; 8/2); data for all MN locations can be viewed at the VegEdge site: 2007 Moth Flight Data

For more information on CEW and ECB management on all crops, see the 2007 Midwest Vegetable Production Guide: http://www.vegedge.umn.edu/intro/vegguide.htm?ID=1179
Midwest Vegetable Production Guide (On-line,  Purdue; PDFs): http://www.btny.purdue.edu/Pubs/ID/ID-56/

For more information on recent trends in CEW Resistance to Pyrethroids, see the 2006 Symposium Papers at Plant Management Network

Note: All UofM Extension, staff and students have free access to Plant Management Network (PMN) journals and content. The full Proceedings is available to subscribers and persons affiliated with partners of the Plant Management Network. Low-cost annual subscriptions may be purchased online at www.plantmanagementnetwork.org/subscriptions. Partner affiliates may sign up free at www.plantmanagementnetwork.org/subscriptions/#complimentary.

 

 

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN).  Reports are posted on the U of MN and MDA web sites on Fridays.  If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us , MDA, 625 Robert St. North, St. Paul, MN  55155.  You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/plants/pestmanagement/ipm/ipmnews.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA).  These institutions are equal opportunity providers.

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 manufacturer directions.

                    

Last Revised July, 2007 by woldx018@umn.edu
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