  We present flavor SU(3) sum rules for $D \to PP$ and $D \to PV$ decay
amplitudes, that are valid to second order in symmetry breaking by the strange
quark mass spurion. Decay rate sum rules are also computed to this order.
Particular attention is given to sum rules arising from the isospin and U-spin
subgroups, the former providing sensitive tests for alternative sources of
SU(3) breaking. We apply the latter together with the postulated $\Delta U = 0$
rule for the large penguin picture to predict the ratio and difference of the
direct CP asymmetries for $D \to KK^*$ and $D \to \pi \rho$.
