Ipyr was a lush, green world; and the primary home-world of House Thorvald, which governed the planet as an Earldom in the Landsraad. During to the first rebellion against Emperor Paul Atreides Muad'Dib, from 10,194 AG to 10,198 AG; led by planetary ruler Memnon Thorvald, the planet was Thorvald's base of operations.
Paul Atreides's forces then "sterilize" Ipyr, using "weapons, explosives, highly toxic chemical bombs, defoliants, and wide-dispersal incendiaries" to destroy every living thing and render the planet uninhabitable.
Sources: Paul of Dune?,
On the net: Dune wikia,