Hello, I have a chestnut orchard which is outside US in a region where no one or only few are growing chestnuts therefore there is limited expertise and knowedge about growing and maintaining chestnuts. Every year I replant around 30-40 % of the orchard mainly due to delayed graft failure, nurseries that sell diseased trees and poor orchard management. That is why I am asking here. 

Recently I have noticed that some of the leaves of some of the trees are turning yellow and I am wondering what might be the cause and would it lead to tree dieback. I have applied biofertiliser Hemozim Bio N5. Thank you