I have an Chinese Elm Tree cultivar "Frosty" . I kept it as a Bonsai for 10 yrs. then planted it in the yard in full sun in a well drained area 6 yrs. ago. It is now 15 feet tall. The last 2 years now again this year it is having pretty severe leaf drop. They yellow and some but not all have holes in the leaf. There seemed to be a lot of ant trails so I doused the trunk with a broad spectrum insecticide. Seemed to alleviate the problem some what last season but this year applied insecticide before it leafed out and it didn't help. Any suggestions ? Thanks Jim