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 Corn Rootworm Product Efficacy Trials, UW-Madison Entomology 2003-2005 Minimize
Location: BlogsWisconsin Crop ManagerInsects and Mites    
Posted by: WCM Staff 1/19/2006 3:00 AM
The impact of corn rootworm larval feeding on corn is evaluated each growing season in replicated small plot trials at the Arlington Agricultural Research Station using the Iowa State University 0 to 3 Node-Injury scale (Oleson et al. 2005). The current article summarizes root-rating results for three years, 2003-2005.

Corn Rootworm Product Efficacy Trials, UW-Madison Entomology 2003-2005

Eileen Cullen, Extension Entomologist,
UW Entomology Department

The impact of corn rootworm larval feeding on corn is evaluated each growing season in replicated small plot trials at the Arlington Agricultural Research Station using the Iowa State University 0 to 3 Node-Injury scale (Oleson et al. 2005). The current article summarizes root-rating results for three years, 2003-­2005. The 0 to 3 Node-Injury scale was featured in Vol. 12, No. 18, July 7 2005 Wisconsin Crop Manager Newsletter “Research Brief: 0 to 3 Node-Injury Scale for Corn Rootworm Rating” http://ipcm.wisc.edu/wcm/pdfs/2005/05-18insect2.html.
 
According to common protocol, corn rootworm efficacy trials are planted each spring into continuous corn ground trap-cropped the previous year with late planted corn to attract corn rootworm beetles and attain heavy rootworm larval pressure in the plots. Treatments are assigned to plots in a completely randomized block design, replicated four times. Plots are 50 feet long x 4 rows wide (30-inch row spacing). Planting dates and subsequent root evaluations occurred May 3 and July 25 (2003); May 5 and July 26 (2004); and May 5 and July 19 (2005).
 
Results for all three years are summarized in Table 1. Five corn plants were evaluated per plot, for a total of 20 roots evaluated per treatment. Plants were cut to within 6 inches of the ground, dug up and removed. Roots were soaked and pressure-washed to remove soil prior to node injury rating. Root ratings between 0.25 and 0.50 or greater fall within potential economic injury range. We use a root rating threshold of 0.50 (some pruning has occurred, but never the equivalent of an entire node) to determine whether a product has provided adequate root protection. Root ratings greater than 0.50 are considered to have provided less than adequate control, and the closer a root rating is to 0.25 or below, the more effective a particular product is for that trial.
 
  • In the UW-Madison trials, soil applied granular insecticides Force 3G and Aztec 2.1G have performed the most consistently when pressure was heavy, resulting in root rating scores below 0.50 over three years in trials
  • The nicotinoid seed-applied insecticides Cruiser and Poncho 1250 at the corn rootworm rate (1.25 mg. per kernel) provided acceptable control in the 2005 trial under moderate rootworm pressure (untreated check 0.7 node-injury score), as did nearly all products tested. However, under heavy rootworm pressure in UW trials 2003-2004 (untreated check node-injury scores 1.14 to 2.02) the seed treatments have not provided adequate root protection.
  • The WI Department of Agriculture Trade and Consumer Protection Pest Survey team completed its annual corn rootworm beetle count in August 2005. A complete report and Wisconsin distribution map can be accessed at WI DATCP’s Wisconsin Pest Bulletin Newsletter, Vol. 50, No. 22, Nov. 4, 2005 http://pestbulletin.wi.gov/. (Click on the Corn link…). Highlights are re-printed in the following paragraph:
 
Corn rootworm - The survey, timed to correspond with peak adult emergence during the first two weeks of August, found high adult rootworm populations across much of the state, with the exception of the north central and northeast districts. The statewide average of  1.6 beetles per plant more than doubled the 0.75 beetle per plant threshold that entomologists consider to indicate a potential for corn rootworm problems in continuous corn the following year. Corn rootworm beetle populations were particularly high in the southwest and southeast districts, where averages of3.2 and 3.8 beetles per plant were recorded, respectively. In addition, the beetle survey showed the western species, Diabrotica virgifera LeConte, to be the dominant species statewide, comprising 58% of all rootworms present.
 
  • Results of the WI DATCP annual corn rootworm beetle survey indicate potential for heavy corn rootworm larval pressure in 2006. Pressure will be influenced by overwintering egg survival and soil moisture conditions during egg hatch following 2006 corn planting, but the general forecast, based on survey results indicates a rootworm year for 2006. The importance of scouting continuous corn fields in August to assess the economic need for a corn rootworm control product the next year was addressed in the Aug. 4, 2005 Wisconsin Crop Manager Newsletter, Vol. 12, No. 22 http://ipcm.wisc.edu/wcm/pdfs/2005/ CullenAu g3.pdf.
 
The February 2006 Wisconsin Crop Manager Newsletter (next issue) will present results from the UW-Extension/WI DATCP survey of the Variant western corn rootworm affecting first year corn. In The February 2006 Wisconsin Crop Manager Newsletter (next issue) will present results from the UW-Extension/WI DATCP survey of the Variant western corn rootworm affecting first year corn. In 2005 the UW-Extension Southeast Wisconsin Variant Trapping Network monitored 71 soybean fields over 11 southeastern and southern WI counties to obtain information on the range expansion of this Variant rootworm strain.
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