We have been using Zylam systemic this year as a soil drench application. This is a preventative application at the higher rate. .75 oz per inch at breast height. I will probably rotate to Imidicloride (sp) next year. We have had them all around the counties in our greater metropolitan area. From what I have found if the tree is 50% or greater affected cut it down. Purdue's website has been most help-ful!