I would suggest using different varieties of aerated compost tea recipes used as a soil and foliar appliation on and around the trees' soil base.

Mix in the tea recipes fish oil, neem oil, cedar oil, and dry molasses products for pest control. You might want to try sulfur products too in the mixture too, if it makes sense to your farming or gardening style.

The aerobic compost tea and molasses products will increase beneficial microbial activity for extra disease and pest protection on the trees' surfaces and near the roots.

Hope this helps.
Happy Gardening!