The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: What do you spray on field corn to control corn flea beetle or do you let it go?
Answer: Flea beetle feeding does not concern us unless:
1) Stewart's disease is a possibility (not in this case),
2) spike to 2 leaf corn is "covered" with them and the corn is not growing due to cool, wet conditions (not a problem now).
In other words, with this weather, I am not recommending treatment for field corn, no matter the number of beetles.
--John Obermeyer, entomologist (5/15/98)