In this Issue:

VEGETABLE NEWS

Vegetable Insect Pest Update

BERRY NEWS

Flower Initiation

APPLE NEWS

Weekly Trap Counts

MDA PUBLICATION

“Greenbook 2007” Highlights Innovative Demonstration Farm Projects

To Our Readers

Order: 2007 Minnesota Vegetable Guide

Insect, Pest Fact Sheets

Vegetable Insect Pest Update

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

The 2^nd flight of European corn borer (ECB) has remained active in several regions of southern MN over the last 2 weeks.  In both St. James (Watonwan Co.) and Owatonna (Steele Co.), black light trap catch peaked at 154 moths per night on 8/14/07.  Trap catches have declined since then but remain relatively high compared to previous years.  If sweet corn is at a susceptible stage (row tassel or later), which should be the case for most acres this time of year, trap catches above 10 ECB moths / night could lead to significant egg lay and ear infestations.  You can follow black light trap catch across the state at http://www.vegedge.umn.edu/2007/MNlist.htm               

Corn earworm (CEW) moth catch in wire-mesh pheromone traps across southern MN increased significantly over the last 2 weeks (see Figure 1).  Several locations have reported one night pheromone trap catches in excess of 500 CEW moths with a peak of 868 CEW at Blue Earth (Faribault Co.) on 8/18/07.  Trap catches at this level indicate a major risk for susceptible sweet corn (silking stage) and application timing is critical to achieving adequate larval control.  We have encountered problems with CEW pyrethroid resistance in the past, but a significant percentage of control can also be lost due to improper timing (Table 1).  Poor control at harvest can also result from insecticides being applied either too early or too late, if the interval between sprays is too long, or a combination of these factors. With numerous rainfall events during the past week (e.g., >3” per day), fresh-market growers relying on ground application equipment will have some challenges.  

Recently, with trends toward pyrethroid resistance in CEW-sweet corn trials in the Midwest, it has been difficult to sort out how much of the loss in control is due to poor timing or resistance. Following the 2006 field season, and evaluation of multiple treatment scenarios, we summarized the results from several studies. Here, we illustrate the contribution of pyrethroid resistance and poor timing (“< optimal timing” in Table 1), we provide a brief summary of results from 2006 late-season CEW-pyrethroid trials at Rosemount, MN.  These results reflect natural CEW pressure under late-season Midwest production, for small plot trials, with primary efficacy limited to eggs and larvae.  Although the results may not be this clear in all trials, we did have sufficient CEW pressure (>0.50 large larvae/ear in untreated check plots) and several key points are instructive:

• Optimal control is defined here, as the 1st spray was applied at 50% fresh-silk, with the 2nd spray applied 3 days later, and the 3rd and 4th sprays at 5-6 day intervals thereafter,
• Less than Optimal control refers to the 1st spray applied too early for CEW (e.g., row-tassel or very early silk), or applied too late (past 50% silk), and subsequent sprays applied at 6-7 day intervals thereafter (i.e, 2nd spray too late, etc.)
• Comparing the 39% control to 100% illustrates the worst-case scenario of poor timing and/or possible resistance (total loss in control =61%),
• Comparing the High Rate (Capture+Warrior) scenario for both “Optimal timing” (100% control) and “< Optimal timing” (58% control), provides a loss in control of 42%,
• Comparing the High Rate (Capture+Warrior) scenario (100% control) to the Standard Rate (0.04 lb ai) treatment (81% control), provides a loss in control of 19%.  This loss in control reflects the loss due to resistance.

Table 1. Summary of selected pyrethroid treatments (max. rate scenario for Capture/Warrior; 4 sprays total) vs. a standard scenario for Capture alone (0.04 lb ai/ac; 4 sprays)*

*Data contributions also from: R. Weinzierl (Univ. of Illinois), Rick Foster (Purdue Univ.), Tom Rabaey (General Mills Corp.), and B. Jensen (Univ. of  Wisconsin).

Again, these same percentages in loss of control will not occur in every trial, but the results do illustrate what may be occurring in many Midwest trials, where the total loss in control is due, in part, to both of these factors.  For example, for other locations, the loss due to pyrethroid resistance could be greater, and/or loss due to poor timing could be greater. We reiterate, when poor overall control is observed, the first action should be to review the timing of all sprays, and ensure adequate calibration of equipment.  If CEW moth flight data are available, also compare the timing of your sprays and peak silk dates to the timing of the moth flight.  If your timings are similar to the optimal timing scenario (for Midwest conditions) and you still see poor control, then resistance is more likely affecting your results.  Finally, this overall “optimal timing” scenario also accounts for many details regarding CEW biology, egg developmental time (3-5 days, avg. summer temperatures, etc.), the use of moth flight action thresholds of 5/night (wire-mesh traps), etc., which is not fully discussed here.  For more information, see the sweet corn chapter in Midwest Vegetable Insect Guide, R. Foster and B. Flood (Editors), Meister Publications (http://www.meisterpro.com/vim/).  

For more recent information on late-season management of CEW in sweet corn, see the August 3, 2007 article (web only), and the August 10, 2007 article of the newsletter.  Progress of CEW trap catch can be viewed on the VegEdge website at http://www.vegedge.umn.edu/2007/CEW.htm

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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.

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Last Revised July, 2007 by woldx018@umn.edu
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