  Dwarf galaxies are dark matter-dominated and therefore promising targets for
the search for weakly interacting massive particles (WIMPs), which are
well-known candidates for dark matter. Annihilation of WIMPs produce
ultra-relativistic cosmic-ray electrons and positrons that emit synchrotron
radiation in the presence of magnetic fields. For typical magnetic field
strengths (few $\mu $G) and $\mathcal O$(GeV--TeV) WIMP masses, this emission
peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio
continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the
LOw-Frequency ARray (LOFAR) to derive constraints on the annihilation cross
section of WIMPs into primary electron-positron and other fundamental
particle-antiparticle pairs. Our main underlying assumption is that the
transport of the cosmic rays can be described by the diffusion approximation,
thus requiring a non-zero magnetic field strength with small-scale structure.
In particular, by adopting magnetic field strengths of $\mathcal O(1\,\mu$G)
and diffusion coefficients $\sim 10^{27}~\rm cm^2\,s^{-1}$, we obtain limits
that are comparable with those set by \emph{Fermi} Large Area Telescope using
gamma-ray observations of this particular galaxy. Assuming s-wave annihilation
and WIMPs making up 100 per cent of the DM density, our benchmark limits
exclude several thermal WIMP realisations in the $[2,20]$-GeV mass range. We
caution, however, that our limits for the cross section are subject to enormous
uncertainties which we also quantitatively assess. In particular, variations on
the propagation parameters or on the DM halo can shift our limits up by several
orders of magnitude (in the pessimistic scenario).
