I am new to gardening. I have NO clue, honestly ....

I planted two pear trees in winter and have kept them hydrated (Abatte and Comice). Two weeks ago the leaves started turning black.

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Most of the leaves, about 80% fell off the trees and yesterday I went back to the garden centre to ask what should be done. The guy was very friendly and he told me :

- to cut all the leaves off and burn them
- the scratch the branches to see if they are green underneath.

He suggested it may be a fungal infection.

Do you think this is good advice? It seems at bit drastic to me.

What are the chances of the leaves returning next spring?
What should I do differently next year?

Thanks for ANY help. As I already mentioned - I am a beginner with all this.