The general conditions for the weak and strong regimes of incompressible magnetohydrodynamic turbulence are derived and studied in the framework of the direct interaction approximation. It is shown that in the framework of the weak turbulence theory, the autocorrelation and cascade timescales are always of the same order of magnitude. This means that, contrary to the general belief, any model of turbulence which implies a large number of collisions among wave packets for an efficient energy cascade (such as the Iroshnikov Kraichnan model), does not represent a model of weak turbulence.
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