In this Issue:


Vegetable Insect Pest Update


Temperature and Apple Size

Weekly Trap Counts

Apple Scab Infections

This is the last regular Newsletter for the season.  Look for our wrap-up edition in late September!

Order: 2008 Minnesota Vegetable Guide

Insect, Pest Profiles

Vol 5 No. 11   August 15, 2008

Vegetable Insect Pest Update

Eric Burkness and Bill Hutchison, University of Minnesota

This week, in the Rosemount, MN (Dakota Co.) area, black light trap catches of European corn borer (ECB) have remained low with less than 5 moths caught per night.  Across the state the 2nd flight has also remained relatively low with trap catches generally below 25 moths per night (see graph).  As of August 12th, we are at 1660 degree days (base 50°F), which should put the peak moth emergence for the 2nd flight sometime early next week. We are also approaching the half way point of the 2nd flight treatment window which ends at 2100 degree days. 

Corn earworm (CEW) moth catch in wire-mesh pheromone traps across the state increased significantly over the last week from averages of less than 5 moths per night to more than 40 moths per night in the Owatonna, MN area (Steele Co.) (see graph).  This level of trap catch represents a significant risk for sweet corn that is in the silking stage.  It may be too early to see the high trap catches of >100 moths/night, we typically see in late August, but these levels are still significant.  Application timing is critical to achieving acceptable control and pyrethroid timing trials conducted at UMORE Park in Rosemount, MN, in 2007 (Table 1), suggest that starting a spray program at row tassel or first silk may not be necessary for CEW.  For example, Treatment #5 (Warrior, 5 sprays) provided control that, statistically, was comparable to the 6 or 7-spray programs, and the first spray was not applied until 100% silk.  These results (and data from previous years) suggest that waiting until peak to late silk, can provide more flexibility in timing insecticide applications for CEW in sweet corn, and can reduce insecticide applications where CEW is the primary target pest.  We recognize that these results are not in agreement with much of the extension guidelines regarding spray timing for CEW, however, we believe we now have enough data to support the concept of waiting until peak to late-silk for the 1st spray.

Also a reminder for managing CEW in 2008, the insecticide, Coragen™ (DuPont), has received Section 18 approval for use in Minnesota, Wisconsin and other Midwest states (see July 11th article for details,  The Sec. 18 label (PDF) can also be downloaded:


click to enlarge click to enlarge


Table 1. The impact of spray timing and total sprays (Warrior, lambda-cyhalothrin) on corn earworm (H. zea) control in sweet corn, Rosemount, MN, 2007*



Mean number larvae per ear

Marketable ears (%)




Rate lb(AI)/ac

Total ECBa

Large CEW (% control)b

Total CEW (% control)c


Total damaged

1. Warrior 7 apps



0.11 (91) c

0.20 (87) b

89 ab

0.80 e

2. Warrior 2 apps



0.89 (25) b

1.40 (7) a

26 c

6.48 b

3. Warrior 6 apps



0.10 (92) c

0.20 (87) b

93 ab

1.09 de

4. Warrior 6 apps



0.05 (96) c

0.14 (91) b

95 ab

0.68 e

5. Warrior 5 apps



0.09 (92) c

0.23 (85) b

91 ab

0.88 e

6. Untreated check



1.18 (--) a

1.51 (--) a

13 c

9.20 a








Means within columns followed by the same letter are not significantly different (P > 0.05), Protected Least significant difference Test (LSD). 

*Spray dates were as follows:
TRT 1 (0% silk emerged)     = 8/10; 8/13; 8/16;           8/21; 8/24; 8/27; 8/30
TRT 2 (~50% silk emerged) =          8/13; 8/16
TRT 3 (~50% silk emerged) =          8/13; 8/16;           8/21; 8/24; 8/27; 8/30
TRT 4 (~90% silk emerged) =               8/15;    8/18;   8/21; 8/24; 8/27; 8/30
TRT 5 (100% silk emerged) =                       8/17;       8/21; 8/24; 8/27; 8/30

a Includes all ECB instars in the husk, silk, tip, side, butt, or shank of the ear.
b Includes CEW that are 3-6th instar in the tip, side, or butt of ear.
c Includes all CEW instars in the tip, side, or butt of the ear.
d Percentage of ears with only small larvae (1-2 instar ECB and/or 1-2 instar CEW) and/or damage limited to the tip; no damage or larvae on the side or butt of the ear.
e Total kernels damaged/ear in the tip, side, or butt by ECB and/or CEW.


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Co-Editors: Bill Hutchison (, Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (, 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, , 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: and at the MDA web site in pdf format at:

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