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Northern Illinois Agriculture

University of Illinois Extension
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Western corn rootworm update

Posted by Russel Higgins -

Now this is January weather, we have just recorded several of the coldest nights since the first day of the year. Today we are sharing research conducted at the Northern Illinois agronomy research Center in 2012 as it pertains to our most destructive corn insect pest, the Western corn rootworm beetle.

Before leaving the topic of weather and insect pests, I am often asked if cold weather has a role in the mortality of the Western corn rootworm beetle, this insect is currently in the soil overwintering as an egg.

A quick synopsis of a Western corn rootworm survival study that was conducted by Mike Gray and Jon Tollefson at Iowa State University during the winters of 1983-1985. That study examined the influence of different tillage methods and winter weather on rootworm egg survival. To aid our memory, the winter of 1983-1984 were characterized by below normal snowfall and temperatures. The mean temperature for December was approximately 15°F colder than average in Iowa. The study indicated that corn rootworm egg survival was affected by tillage during a severe winter (1983-84). Egg survivorship was reduced by about 63-75 percent in plots that had been para plowed and mold-board plowed during the fall. However, there was no significant reduction in egg survivorship in plots that were no tilled or chisel plowed. During the more moderate 1984-1985 winter, mortality seems to be negligible; there were no significant differences among the four tillage methods.

The researchers provided the following summary

If a rootworm population reduction was to occur, then three conditions would have to be met:

  1. severe cold
  2. absence of an insulating snow cover, and
  3. mold-board tillage in the field.

Despite the temporary weather conditions, unless fields were moldboard plowed, I would not expect a significant increase in rootworm mortality from the winter of 2012-13. (Unless we have a dramatic shift in weather patterns).

Let's move on to the 2012 Western corn rootworm research shared by Dr. Mike Gray at the Corn and Soybean Classic last week in DeKalb County ,

 

  • On-farm research in the early 1990s revealed that 26 of 58 producers' continuous cornfields had root injury at or above the economic injury index.
  • Presently, only three Bt proteins offer protection against corn rootworm larval injury: mCry3A, Cry34/35Ab1, and Cry3Bb1.
  • Field level resistance has been confirmed to the Cry3Bb1 protein in some areas of NE Iowa and NW Illinois.
  • An escalation of soil insecticide use is anticipated for 2013, including use on corn rootworm Bt hybrids.
  • Recently published research indicates that for every 1 node of roots pruned by corn rootworms, a 15% yield loss may occur.
  • At the DeKalb location in 2012, yield reductions were very severe when only a soil insecticide was used on certain non-Bt hybrids.
  • At the DeKalb location in 2012, yield benefits differed across the Bt hybrids when a soil insecticide was used. Only Agrisure 3000GT (Garst 84U58 3000GT) benefited significantly from a soil insecticide treatment.
  • Additional research is required to determine the Insect resistance management effects of using a soil insecticide along with a Bt hybrid where resistance to a Bt protein has occurred.

The 2012 report of entomology research is now available at the on Target web site

http://ipm.illinois.edu/ontarget/


 



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