  The ground state of nanowires of single crystalline Pyrochlore
Y$_2$Ir$_2$O$_7$ is a density wave. Application of a {\it transverse} magnetic
field increases the threshold electric field for the collective de-pinning of
the density wave state at low temperature, leading to colossal
magnetoresistance for voltages around the de-pinning threshold. This is in
striking contrast to the case where even a vanishingly small {\it longitudinal}
magnetic field sharply reduces the de-pinning threshold voltage resulting in
{\it negative} magnetoresistance. Ruling out several other possibilities we
argue that this phenomenon is likely to be a consequence of the chiral anomaly
in the gapped out Weyl semimetal phase in Y$_2$Ir$_2$O$_7$.
