The theory of m-th root Finsler metrics has been applied to Ecology, Biology,
Seismic Ray Theory, Gravitation, etc. It is regarded as a direct generalization of Riemannian
metric in a sense, that is, the second root metric is a Riemannian metric.
On the other hand, the Riemannian curvature faithfully reveals the local geometric
properties of a Riemann-Finsler metric. In this paper, we study the class of quintic
(alpha; beta)-metrics. We show that the every 5-root (alpha; beta)-metrics with the scalar flag curvature
K is a weak Berwald metric if and only if F is a Berwald metric and K = 0.
Then, F must be locally Minkowskian.