Apparently this is no longer much of an issue. Quoting [0]:
"The federal ban was lifted in 1966, though many states maintained their own bans. Research showed that blackcurrants could be safely grown some distance from white pines and this, together with the development of rust-immune varieties and new fungicides, led to most states lifting their bans by 2003. Blackcurrants are now grown commercially in the Northeastern United States and the Pacific Northwest. Because of the long period of restrictions, blackcurrants are not popular in the United States, and one researcher has estimated that only 0.1% of Americans have eaten one. [...] By 2003 restrictions on Ribes cultivation had been lifted across most of the states, though some bans remain, particularly on the blackcurrant. State laws are enforced with varying degrees of efficiency and enthusiasm; in some states, officials effectively ignore the ban."
[0] https://en.wikipedia.org/wiki/Blackcurrant_production_in_the...