  Two coherent radio emission mechanisms operate in stellar coronae: plasma
emission and cyclotron emission. They directly probe the electron density and
magnetic field strength respectively. Most stellar radio detections have been
made at cm-wavelengths where it is often not possible to uniquely identify the
emission mechanism, hindering the utility of radio observations in probing
coronal conditions. In anticipation of stellar observations from a suite of
sensitive low-frequency ($\nu\sim 10^2\,{\rm MHz}$) radio telescopes, here I
apply the general theory of coherent emission in non-relativistic plasma to the
low-frequency case. I consider the recently reported low-frequency emission
from dMe flare stars AD Leo and UV Ceti and the quiescent star GJ 1151 as test
cases. My main conclusion is that unlike the cm-wave regime, for reasonable
turbulence saturation regimes, the emission mechanism in metre-wave
observations ($\nu\sim 10^2\,{\rm MHz}$) can often be identified based on the
observed brightness temperature, emission duration and polarisation fraction. I
arrive at the following heuristic: M-dwarf emission that is $\gtrsim
\,$hour-long with $\gtrsim 50\%$ circular polarised fraction at brightness
temperatures of $\gtrsim 10^{12}\,$K at $\sim 100\,{\rm MHz}$ in canonical
M-dwarfs strongly favours a cyclotron maser interpretation.
