Cutting out black knot in a new tree

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I planted this adirondack apricot last year and it devloped black about a month after i planted it. I cut it out last September and sanitized with diluted bleach. You can see the scar. I left the little low branch to grow in beacuse…well plan B.
Looks like plan is up. Whats the best time to snip that infected part off? Should i do something special, like tar cote it?

i had a Adirondack gold apricot that grew to a beautiful 10ft. tree. then suddenly it just died over winter. it wasn’t a particularly cold one either. ive read its common with this tree.