  We study the dominant non-perturbative power corrections to the ghost and
gluon propagators in Landau gauge pure Yang-Mills theory using OPE and lattice
simulations. The leading order Wilson coefficients are proven to be the same
for both propagators. The ratio of the ghost and gluon propagators is thus free
from this dominant power correction. Indeed, a purely perturbative fit of this
ratio gives smaller value ($\simeq 270$MeV) of $\Lambda_{\ms}$ than the one
obtained from the propagators separately($\simeq 320$MeV). This argues in
favour of significant non-perturbative $\sim 1/q^2$ power corrections in the
ghost and gluon propagators. We check the self-consistency of the method.
