UW Extension and IPM Program
Corn rootworm egg hatch has been underway in southern Wisconsin for a short period of time. Not that you would expect to see above ground symptoms, but it is a good time to start thinking about and preparing for root evaluation and beetle scouting. Never have these two practices been more important. Wisconsin is in a unique situation with respect to rootworm resistance management. We can have an impact on the “resistance curve” if we incorporate beetle scouting and root monitoring into our routine.
Scouting for beetles during the egg laying period (early/mid-August to early September) will provide information that is essential to delaying resistance. Beetle numbers have been low in recent years and field counts will give you information necessary to determine IF rootworm protection is needed next year and which control tactic may be best suited for individual field needs. Thus, reducing reliance on a single management tactic.
Monitoring roots for larval damage should begin by the end of July and be completed before significant root regeneration takes place. Using the Iowa State Nodal Root Rating Scale will quantify the amount of feeding and indicate if your current rootworm management practice is working, if you had root injury on first year corn and especially if your Bt trait(s) are working.
There are several resources available which can help you gain experience with both practices and are listed below.
Corn Rootworm Rating
Corn Rootworm Beetle Scouting
IPM Decision Aid: Managing corn rootworm Bt resistance
Corn Rootworm: How to Validate Your Management Decision (Video)
How to Scout for Rootworm Beetles (Video)
Corn Rootworm Damage and Root Node Injury Scoring