What's the best grease to use on the trunk of fruit trees and at what height should the grease be at?
I use a 4" high thick coating of Vaseline John, around the trunk just below where the first branch comes out of the trunk. You can also buy grease bands from garden centres. I renew it yearly or if I accidentally rub any off in the normal course of gardening. One thing to realise is that ants will climb other nearby plants to get to the tree, so leave plenty of space around your fruit trees or cut-down the parts of any other plants which touch the tree above where you placed the grease band.