  Perturbation series in QCD are generally asymptotic and suffer from so-called
infrared renormalon ambiguities. In the context of the standard operator
product expansion in MS-bar these ambiguities are compensated by matrix
elements of higher dimension operators, but the procedure can be difficult to
control due to large numerical cancellations. Explicit subtractions for matrix
elements and coefficients, depending on a subtraction scale R, can avoid this
problem. The appropriate choice for R in the Wilson coefficients can widely
vary for different processes. In this talk we discuss renormalization group
evolution with the scale R, and show that it sums large logarithms in the
difference of processes with widely different R's. We also show that the
solution of the R-evolution equations can be used to recover the all order
asymptotic form of the singularities in the Borel transform of the perturbative
series. For the normalization of these singularities we obtain a quickly
converging sum rule that only needs the known perturbative coefficients as an
input. This sum rule can be used as a novel test for renormalon ambiguities
without replying on the large-beta_0 approximation.
