Official restriction on trade of wild borage grown around start of May (7)

I believe the answer is:

embargo

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'official restriction' is the definition.
'embargo' can be an answer for 'restriction' (thesaurus). I am unsure of the 'official' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for embargo that I've seen before include "Prevent publication" , "Prohibit" , "Official ban on trade or commerce" , "Ban on commerce - mob rage (anag)" , "Legal stoppage of commerce" .)

I've seen this clue in the Irish Times.

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