Triple Massey products over global fields

Let $K$ be a global field which contains a primitive $p$-th root of unity, where $p$ is a prime number. M. J. Hopkins and K. G. Wickelgren showed that for $p=2$, any triple Massey product over $K$ with respect to ${\mathbb{F}}_p$, contains 0 whenever it is defined. We show that this is true for all primes $p$.