Since netherwart and warpedwart are naturally generated, they should have assigned tool, and probably also can_decay block data. Now collecting wood from fungi is extremaly messy (left floating canapies) or extremaly slow (collecting warts by hand).
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It would be feature request if devs wouldn't add natural generation of those blocks in large quantities. Now, since 20w06a, I consider this a bug.
This is more of a feature request than a bug report :T