After dormant basal spraying buckthorn will it still leaf out in spring? Does it leaf out, then die? If it leafs out does that mean the basal spraying was ineffective?
Wouldn't be unusual to see an initial greenup. In spring dormant trees release all of there energy that was stored in the root system back up into the tree. This will also carry the tricopyr with it. You may also see shoots coming off the roots depending how effective the kill was.
I don't use a sprayer. I use a dish soap bottle and apply a ring around the tree about 8" above the root collar area. Have had good results.
At this point, watch & wait. Can take awhile for complete kill to occur. I have had trees rebound year after spraying and then die the next year.