  The field induced switching of conductance in the charge ordered half-doped
manganites is controlled by the combination of metastability, an inhomogeneous
high field state, and cation disorder. We study this non-equilibrium problem
via real space Monte Carlo on a disordered strong coupling model appropriate to
the manganites. We reproduce the variation of the switching fields with the
mean ionic radius r_A and cation disorder \sigma_A, and demonstrate how the
experimental features arise from the proximity of several phases in the Landau
free energy landscape. Our prediction for the field melted state is consistent
with a growing body of experimental evidence.
