I planted three of these beautiful trees in early May and all are doing great. However, one tree has developed what appears to be small holes near the bottom of the tree trunk and sap is running out of these holes. Over the last two weeks, the number of holes and resulting sap flow has increased.

I applied some Malathion solution around the base of the tree two weeks ago and again today.

Questions: What is the cause of the holes and sap? And, is the Malathion the right treatment?

Thanks for your help.