Electromagnetic interference inJψdecays

We point out the importance of properly separating the electromagnetic and "direct" contributions to $\psi$-particle exclusive decay modes before a meaningful comparison with theoretical predictions can be made. This is illustrated using the decays $\frac{J}{\psi }\to \rho \pi$ and $\frac{J}{\psi }\to K{K}^{*}\mathrm{}\left(892\right)\mathrm{}$ with particular attention to tests of the SU(3) properties of $\frac{J}{\psi }$. An experiment is suggested to observe the effects of electromagnetic interference in $e^{+}{e}^{-}\to \rho \pi$ just below the $\frac{J}{\psi }$ mass, and its implications are discussed.