The treatment of Alfv¿n wave mode decay by Cohen and Dewar (1974) is extended to a regime of finite temperature and large acoustic wave damping rates for a model (Lorentzian) Alf¿n wave power spectrum. When applied to hydromagnetic waves in the solar wind, the theory predicts a degradation of the low-frequency (~ (1 day)-1) portion of the spectrum on a time scale of the order of the time required for such waves to travel several AU.