We consider an integrated maintenance/production and spare parts optimization problem for components of a wind turbine farm for which the degradation level is observable. Degradation is modeled as a function of the current operating mode. The spare parts are stocked at a local inventory. The costs associated with spare parts deliveries and part replacements depend on the operating mode. Our objective is to optimize the total discounted cost of maintenance, production and spare part related costs over a finite planning horizon. We formulate the problem the structure of the optimal policy, which is shown to be a bi-threshold policy in each operating mode. Our numerical experiments show that the cost savings obtained by the integrated optimization of maintenance, production and spare parts are significant.