Permaculturists have been using physical methods for years to stop ants protecting aphid herds -- you may not need any chemicals at all. Hunt around for some h

Permaculturists have been using physical methods for years to stop ants protecting aphid herds -- you may not need any chemicals at all. Hunt around for some half-donut shapes that clip around the trunk that you can fill with water. (I can't find any pics after a quick search, but I know they exist.) Otherwise, maybe something mild like a vaseline barrier - probably need to protect from the rain, of course.