Northern Illinois Agronomy Research Center

Department of Crop Sciences---University of Illinois

COLLEGE of AGRICULTURAL, CONSUMER AND ENVIRONMENTAL SCIENCES

FEBRUARY 2002 Newsletter Issue 19:1 Lyle Paul - Agronomist David Lindgren - Farm Foreman 14509 University Rd. Shabbona, Il 60550 Phone/Fax 815/824-2029 e-mail lylepaul@illinois.edu

2001 Growing Degree Days (Base 50)

2001 Precipitation (Inches)

Western Corn Rootworms in Northern Illinois- How close has the rootworm that lays eggs in soybeans gotten?

One of the main questions for corn growers for 2002 is if they will need to apply an insecticide on first year corn following soybean or will the corn and soybean rotation continue to effectively control the rootworm population. This question arises from the behavioral adaptation of the western corn rootworm (WCR) adults to lay eggs in soybean fields so the eggs will be there the next spring to hatch and the larva feed on the corn roots. This problem started in east central Illinois and has spread from there. The short answer to the question on the need to use an insecticide in this general area from Kevin Steffey and Mike Gray is that they are not sure.

The only way to determine if you would need to apply an insecticide in 2002 is to have put yellow sticky traps in the soybean fields for a four-week period in July and August of 2001. The other problem with the results from this scouting technique is that the traps do not indicate what is happening in an entire area, but just what the expected population of rootworms will be in that specific field.

To try and help determine the movement activities of the WCR, corn and soybean fields at NIARC, (DeKalb Co.), Northwestern Agricultural Research Center (Warren Co.), Orr Agricultural Research Center (Pike Co.), Dixon Springs Agricultural Center (Pope Co.) and near Urbana (Champaign Co.) have been monitored for the past four years. This has been a cooperative effort with Drs. Eli Levine and Joe Spencer from the Center for Economic Entomology, Illinois Natural History Survey. The following is a summary of their findings presented in a poster at the Entomological Society of America, San Diego, CA. 8-12 December:

Levine, E., J.L. Spencer, E.A. Adee, R.A. Hines, L.E. Paul, G.A. Raines, T.R. Mabry, and S.A. Isard. 2001. Disperal of western corn rootworm adults from cornfields into soybean fields at sites in Illinois where crop rotation is still effective and where it has failed.

Results
Although WCR adults were found in corn at all sites in 1998, WCR were scarce in the soybean vial traps at the four remote sites (DeKalb, Warren, Pike and Pope Co.). At Champaign Co., WCR were initially detected in corn and remained most abundant there for approximately 3 weeks. After July 29, WCR population densities increased in soybeans and rapidly exceeded those in corn. WCR movement into soybeans occurred even while fresh to light brown corn silks were available and beetle densities in corn were fairly low. Consistently high numbers of WCR were captured up to 120 meters into the interior of the Champaign Co. field. The DeKalb Co. site differed from the other remote sites in 1998 in that the soybean border trap caught nearly as many beetles as some traps in corn; for the most part, these beetles were captured in soybeans later in the season, (August 26).

The 1999 results were similar to the 1998 results at all sites except DeKalb Co. where WCR abundance in soybeans was similar to abundance in corn. As the season progressed, WCR captures in DeKalb Co. soybean vial traps eventually overtook those in corn (August 19) a pattern typical of problem area (July 22), but occurring approximately a month later in the season. During the 1999 field season, reports of larval injury to corn planted fol-lowing soybeans and capture of WCR adults on yellow sticky traps in soybean fields in DeKalb Co. were reported.

In 2000, extremely few WCR were again captured in vial traps in soybeans in Warren and Pike Co., despite the capture of large numbers of WCR in vial traps in corn. Fairly large numbers of WCR were captured in vial traps in soybeans in DeKalb Co., but captures never exceed that in corn. In Champaign Co., capture of WCR in soybean overtook that in corn very early on in the season (July 20).

In 2001, the same pattern of very few WCR being captured in vial traps in Warren, Pike and Pope Co. appeared. As in 1999, total WCR capture in soybeans was similar to that in corn for DeKalb Co.; WCR capture in soybeans overtook that in corn about August 15. As in earlier years, capture of WCR in soybeans overtook that in corn very early in the season for Champaign Co. (July 25).

Conclusions:

1. High abundance of WCR adults in soybean fields continue to distinguish problem from non-problem areas.

2. Spread of the WCR biotype that lays eggs outside of cornfields is moving very slowly from its presumed origin in east central Illinois to the north, south and west. The pattern of adult WCR movement from corn into soybeans in DeKalb Co. now matches that of problem areas. Warren, Pike and Pope Co. appear to be unaffected by the new biotype at the present time.

That is the end of the printed portion of the poster. Additional details on the poster included the number of WCR adults captured in the vial traps at the Warren, Co., DeKalb Co. and Champaign Co. locations. In 2001, the peak capture of WCR adults in soybean field vial traps for any week in Champaign Co. was about 83 WCR. The peak capture of WCR adults in soybean field vial traps for any week in DeKalb Co. was about 8. The WCR adult capture at each of the soybean field vial traps in DeKalb Co. was about 10% of the WCR adult capture in the soybean field vial traps in Champaign Co.

Other indicators to consider, the area south of Yorkville has problems in first year corn fields in 2001. The area north of Yorkville, for the most part, did not appear to have problems in 2001. A field about 3 ½ miles from the Research Center with sticky traps this past summer had less than ½ the number of beetles caught to justify treatment in 2002.

Steffey’s and Gray’s recommendations are that if you or your neighbors had problems in 2001, you probably should treat with a rootworm insect-icide this year. They would also recommend you put sticky traps in soybean fields this year to determine if you will need to treat first year corn in 2003. Another point to remember is that from Steffey and Gray’s work from the early 90's, in continuous corn, about ½ of the fields did not have sufficient root damage to have justified insecticide application. All of these points should be included in the decision-making process when deciding on insecticide use for first year corn following soybeans. Unfortunately, there is no easy straight forward answer to the question on insecticide use for first year corn.

WCR Web Page
Another resource that could be helpful for learning more about corn rootworms is:
http://www.ipm.uiuc.edu/fieldcrops/insects/western_corn_rootworm/

This site also has information on how to scout fields and survey results form 2000 by county.
Survey results form 2001 are available at: http://www.staff.uiuc.edu/~s-isard

Internet newsletter:
The newsletter has come through the mail on an irregular basis. We will continue to do that. If you would like your name removed from the mailing list, please let us know. If you would prefer to get the newsletter as an e-mail attachment, please e-mail me at:lylepaul@illinois.edu with the version -Word Perfect or Word you would prefer. For address corrections, e-mail, write or call to the address at the top of the newsletter.

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