In this issue
Sweet Corn Insect Pest Updates
Check Hybrids for Corn Rust Resistance!
Regional Analysis of Pyrethroid Efficacy Against European Corn Borer in Late-season Sweet Corn
| Vol. 2 No. 10 | July 21, 2000 |
Regional Analysis of Pyrethroid Efficacy Against European Corn Borer in Late-season Sweet Corn
Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul, Minn.
I am often asked which pyrethroid insecticide performs best against European corn borer in sweet corn. My answer is typically based on the most recent data available. However, relying on 1-2 years of recent data, or the results from 1-2 locations, does not always provide the most complete answer. With the following analysis, I have explicitly incorporated the results from 23 trials conducted over the past 10 years. Although insecticide efficacy is just one of many issues to consider in developing an IPM program for a given crop, it is nevertheless a key element that deserves more attention. In particular, I believe that with many pest management tactics (e.g., resistant varieties, biological control and chemical control) it is useful to look at the risks (variability) with specific pest control tactics as well as the expected mean (average) level of control.
With this preliminary analysis, I provide one approach to summarizing multiple studies to assess the efficacy of four primary pyrethroid insecticides currently labeled for ECB control in sweet corn. Although this particular summary does not use the formal statistical methods to analyze treatment effects across studies (i.e., formal meta-analysis), it is similar to a meta-analysis in that I have conducted a careful evaluation of multiple trials (multiple researcher, locations, and years), where similar protocols were used.
Click here to print the graph.
Key for lb ai to product/ac rates:
Capture 0.03, 0.04 lb ai=2.1 and 2.5 fl oz product/ac respectively
Warrior 0.02 , 0.025 lb ai=2.6 and 3.2 fl oz product/ac, respectively
Baythroid 0.031, 0.0375 lb ai=2.0 and 2.4 fl oz product/ac, respectively
Pounce 0.15, 0.20 lb ai=6.0 and 8.0 fl oz product/ac, respectively
Click here to print the graph.
Protocol: Data sets for analysis were collected from published reports in Arthropod Management Tests, Entomol. Society of America, and unpublished annual reports from extension entomologists throughout the Midwest. States currently represented in the data set include: MN, WI, IN, IL, OH and PA. All data for this analysis met the following criteria: late-season sweet corn trials (typically conducted between July-Sept.) for Midwest U.S. latitutudes, standard randomized complete block designs with at least 4 replications, a minimum of 25 ears/replication examined (100 total/treatment), minimum of 30% ear infestation in the untreated check plots, and the timing of the first spray ranging from row tassel to 20% silk. Based on typical Midwest summer temperatures, the time period ranges from 28 days before harvest (dbh) at row tassel to 21 dbh for first silk. A total of 23 trials were found to meet all of the criteria. However, each trial did not always include all treatments; current sample size (n) for each treatment is: Capture 0.03 (15), Capture 0.04 (12), Warrior 0.02 (20), Warrior 0.025 (22), Baythroid 0.031 (11), Baythroid 0.0375 (7), Pounce 0.15 (18), and Pounce 0.20 (15). The mean number of sprays ranged from 2 to 6/trial (mean of 3.6 sprays), and the ear infestation in the untreated check plots ranged from 0.28 to 3.9 late-instar (3-5th) ECB larvae/ear (mean of 1.2/ear).
Results: The enclosed figure summarizes the mean and 95% confidence interval (CI) of percent ECB control for each pyrethroid. The CI should be interpreted as we have 95% confidence that the actual mean, lies within this range. As expected, all four insecticides, at each respective rate, provide a high level of control (mean from 94-99%) against ECB. However, there is a considerable variation in control based on the 95%CI. The treatments with the highest level of control also have more narrow confidence intervals. Where confidence intervals overlap, it is likely there is no significant difference in control.
NOTE: At least two additional key factors that will influence the variability in percent control (risk of poor control), including: a) timing of FIRST application (i.e., first spray should be at 28 dbh, row tassel, to minimize the chance of late-instar larvae in ears at harvest, and b) inherent varietal differences (e.g., longer, tighter husk cover can have a tremendous impact on reducing final at-harvest infestations in ears).
In summary, this is a very basic statistical summary of the data currently available (n=23 trials). Additional analyses are underway which will dexcribe the probability of x level of control, include additional data sets for the pyrethroids, evaluate new products such as SpinTor, and focus on corn earworm in sweet corn as well as other vegetable insect pests. Much of this information will be provided in upcoming issues of the newsletter.
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 12,
2001.
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