The Irish province crossed for a team-record 10 tries against the South African side, powerhouse forward Botha touching down twice in the first half either side of a Calvin Nash score at Thomond Park.
Jack O'Donoghue also dotted down before half-time and John Hodnett registered a debut try shortly after the restart, while Neil Cronin, Shane Daly and Dan Goggin all went over.
Arno had his hat-trick with five minutes remaining and Daly scored a second as Munster moved top of Conference B.
Glasgow Warriors was also emphatic as it battered Zebre 56-24 in a high-scoring affair at Scotstoun.
George Horne and Mesu Dolokoto each scored twice as the Warriors ran in seven tries.