Beginning in the summer of 1993, county extension educators
and Purdue University Extension Specialists identified western corn rootworm
larvae, Diabrotica vergifera virgifera, (WCR) in a cornfield that
had been planted following soybean. Corn roots exhibited root pruning and
some
plant lodging, typical to damage associated with Indiana’s predominant species
of rootworm. Initially, specialists felt that the discovery was simply an
abnormality and dismissed the occurrence as a onetime event. However, in
the following
summer additional cases of corn rootworm feeding on first-year corn were
discovered in the area. In subsequent years the phenomenon continued to increase
in regularity
throughout several counties in West Central Indiana and East Central Illinois.
In some locations, summer thunderstorms and associated strong winds resulted
in significant plant lodging and yield loss.
Prior to the mid 1990s, farmers rarely applied a rootworm insecticide on
corn following soybean according to university recommendations. Previously,
WCR
larvae were only associated with corn planted into corn or popcorn residue.
As the number of cases of corn rootworm larvae feeding on first-year corn
began to increase, growers gradually began implementing rootworm insecticide
treatments
into their pest management program. It is now estimated that 85% of first-year
corn acreage in the region, or nearly 600,000 acres are being treated with
a soil insecticide for control of corn rootworm larvae. In addition, there
is evidence that producers in other regions of Indiana are increasing their
use of soil rootworm insecticides as a precautionary measure, despite documentation
that this phenomenon does not yet exist in their areas. The shift in behavior
or adaptation of WCR in this region, Indiana’s most productive land, has
virtually eliminated the benefit of crop rotation as a best management practice
for controlling
corn rootworm larvae.
Over the last several years, Purdue University Entomologists in cooperation with County Extension Educators have studied the development of WCR damage in first-year corn. Researchers believe that this WCR variant is likely caused by a genetic change in the insect population and/or the insect may be adapting its behavior to crop rotation by laying eggs in soybean. Researchers have also conducted field trials throughout the affected region and developed an effective IPM protocol that relies on scouting and thresholds to identify fields that are candidates for economic larval damage in next year’s corn.
For more information please consult Entomology publications E-49 and E-218.
These publications are in Adobe Acrobat PDF format. To read, download, or print the materials, you will need the free Acrobat Reader, available from the Adobe web site. |
