I've had a mulberry tree for the past forty five years. It was fruiting heavily with almost a carpet of fruits falling. This year there were only a few fruits. Can it be due to any disease of the tree or any chemicals in the soil?
There could be many reasons:
- Rain or frost during flowering.
- Poor soil (after 45 years the mulberry could have "eaten" much of the nutriments)
- Wrong pruning: old branches will not produce fruits, but also the very young (of the last year).
or also diseases or chemicals (as you wrote), but I think you will have noticed that from other signs (e.g. leaves).