  Pulsar Timing constraints on scalar-tensor theories with conformal and
disformal couplings to matter are discussed. Reducing the dynamics to the
motion in the centre of mass frame and using the mean anomaly parametrisation,
we find the first post-Newtonian corrections induced by the conformal and
disformal interactions in the form of a generalized quasi-Keplerian solution.
We also derive the radiation reaction force due to scalar radiation and the
corresponding Post-Keplerian Parameters (PKP). We use different pulsar time of
arrival (TOA) data sets to probe the scalar corrections to the PKP. In
particular, we focus on systems with large orbital frequencies as the
contributions to the PKP terms induced by the disformal coupling are sensitive
to higher frequencies. We find that the most constraining { {pulsar timings}}
are PSR B1913+16 and the double pulsar PSR J0737-3039A/B, being {{of the order
of}} the Cassini bound on the conformal coupling obtained from the Shapiro
effect in the solar system. { {The combined constraints using other pulsar
timings give an upper bound on the conformal coupling $\beta^2 < 2.33 \cdot
10^{-5}$ and a lower bound on the disformal coupling scale of $\Lambda \geq
1.12 \ {\rm MeV}$ which is comparable to the Cassini bound and to the GW-170817
constraints respectively}}. Future measurements for pulsar timing with black
hole companions are also discussed.
