Let K be the function field of a smooth, irreducible curve defined over Q. Let f ∈ K[x] be of the form f (x) = x q + c where q = p r , r ≥ 1, is a power of the prime number p, and let β ∈ K. For all n ∈ N ∪ {∞}, the Galois groups Gn(β) = Gal(K(f −n (β))/K(β)) embed into [Cq] n , the n-fold wreath product of the cyclic group Cq. We show that if f is not isotrivial, then [[Cq] ∞ : G∞(β)] < ∞ unless β is postcritical or periodic. We are also able to prove that if f1(x) = x q + c1 and f2(x) = x q + c2 are two such distinct polynomials, then the fields ∞ n=1 K(f −n 1 (β)) and ∞ n=1 K(f −n 2 (β)) are disjoint over a finite extension of K.