Stopping ants farming aphids on apple trees

Hello,

Just joined the forum to see if there is anyone out there who can help me stop ants farming aphids on my apple trees. We have a healthy ant population in the garden, would be happy to let them be - but they are farming aphids on all the apple trees. So far have tried:

Many kettles of boiling water

Tree grease (but most are cordons so the ants just go up the wall instead)

Spraying the aphids

Diatomeous Earth

Ant powder

Bait stations

Have seen a product that involves a 'natural' nematode predator and wondered if anyone has used this with any success?

Otherwise I am now running out of ideas!