CREATE TABLE table_78209 ("Date ( s )  conducted" CLOB, "Polling organisation/client" CLOB, "Cons" CLOB, "Plaid Cymru" CLOB, "Lib Dem" CLOB, "Others" CLOB, "Lead" CLOB)

Tell me the dates conducted for plaid cymru of 19%
SELECT "Date(s) conducted" FROM table_78209 WHERE "Plaid Cymru" = '19%'
SELECT "Date(s) conducted" FROM "table_78209" WHERE "Plaid Cymru" = '19%'