The following question was sent to the P&PDL diagnosticians here at Purdue University:

corn fleaQuestion: 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)