There is nothing selective that will kill kudzu and not injure pine trees. I would cut the kudzu off at ground level and then spray the freshly cut stubs with glyphosate (Roundup). Do not allow the glyphosate solution to come in contact with any desirable vegetation. Perform this task from August to October and repeat the process if you see re-sprouting. There are other stronger chemistries reserved for professionals that you may not have access to. Glyphosate has no soil activity so the pine trees' root system will not absorb it so no damage should be observed from root uptake.