Hello Garden Guy,
I wouldn't know of any chemical, I'm O~Natur~el
but, my only suggestion to keep that bug away is,
Keep their growing environment pretty much almost what they like...And they won't send out distress calls to bag bugs saying they are sick........
(does that make sense??)
Especially, keep them on top of the dirt, good draining dirt and nothing on top of them~like compost or dead leaves...And maybe divided every so many years to keep them vigorous!!!!

Weezie

* * * *
Weezie

Don't forget to be kind to strangers. For some who have
done this have entertained angels without realizing it.
- Bible - Hebrews 13:2





http://photobucket.com/albums/y250/weezie13/