  Cosmic strings are potential gravitational wave (GW) sources that can be
probed by pulsar timing arrays (PTAs). In this work we develop a detection
algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes
PTA data. We find four events with a false alarm probability less than 1%.
However further investigation shows that all of these are likely to be
spurious. As there are no convincing detections we place upper limits on the GW
amplitude for different event durations. From these bounds we place limits on
the cosmic string tension of G mu ~ 10^{-5}, and highlight that this bound is
independent from those obtained using other techniques. We discuss the physical
implications of our results and the prospect of probing cosmic strings in the
era of Square Kilometre Array (SKA).
