Just as you finish up dealing with the onslaught of western corn rootworm beetles clipping silks in your corn this year, you need to be getting ready to monitor your soybean fields. Population monitoring of the western corn rootworm beetle should be underway in soybean fields this last week of July. Soon you'll note soybean fields in your area with yellow sticky traps in them. What are they doing? The yellow sticky traps are out there to monitor adult western corn rootworm (WCR) beetle populations to predict what will happen in that field when corn is planted in it next spring. WCR has been a persistent problem, okay a horrendous problem, in the east central part of Illinois and has spread to the north and west and just a bit south.

The larval stage of the western corn rootworm is what causes damage to corn roots resulting in poor small root systems and goose necked stalks. Did western corn rootworm larvae cause damage to corn roots in your field this season in your first year corn? Did you treat with a granular insecticide at planting to control the larval stage? Did you need to?

The threshold for damage was developed using Pherocon AM unbaited yellow sticky traps. You need a minimum of twelve traps per field for four weeks, that's forty-eight traps. Your first set of twelve Pherocon AM yellow sticky traps should be placed in an equidistant grid in the field this week. Place the traps just above the soybean canopy each week. Change the traps once a week for a total of 4 weeks. When you collect the traps each week bring some plastic wrap with you to put over the individual collected traps. You can stack them up then as you collect them. If you don't want to count the number of beetles on the traps right away then put each in a plastic bag, label them and place the collected traps in a refrigerator. The insect fauna on the traps will begin to deteriorate pretty rapidly if you don't store them this way.

Count up western rootworm beetles on the traps for the whole monitoring period; calculate beetles per trap per day. The threshold for treatment is 5 or more beetles per trap per day. Our IPM website with additional information is http://www.ipm.uiuc.edu/fieldcrops/insects/western_corn_rootworm/index.html

If you monitor soybean fields that will be planted to corn next season you will have field specific information on whether your first year corn will need an insecticide application, otherwise your decision will just be a guess. This is an expensive guess to make as well with the price of insecticide application ranging from $16 to $30 acre. Monitoring an entire soybean field will cost you around $80 and some sweat equity. But, you will have the information you need next season to make the best environmentally sound pest management decision. Should your monitoring indicate that insecticide application is warranted then check out our recommendations for insecticide consistency and efficacy that are reported each year in our "Bulletin" at http://www.ipm.uiuc.edu/bulletin/index.php , it is worth your effort to check out the results when they come in.

For more information contact Suzanne Bissonnette (217) 333-4901.