Techniques for controlling loading on a wind turbine blade in the flap-wise direction. A system model has a description of flap loading on the blade and is used to predict flap loading on the blade over a prediction horizon using the system model. A dynamic flap loading limit is determined based on predicted flap loading and a measured flap loading, and a constraint is defined to limit flap loading on the blade based on the dynamic flap loading limit. The predicted flap loading is used in a cost or performance function, and the cost function is optimized subject to the constraint to determine pitch for the blade to control flap loading on the blade. Advantageously, the dynamic limit varies based on discrepancies between predicted and measured flap loading to allow for adaptive back-off from extreme loads prior to such loads building up or being exceeded.