The ability of Xylella fastidiosa (Xf), the causal agent of Pierce’s Disease in grapevine, to systemically colonize the xylem directly correlates with symptom development. Xf facilitates its colonization of the xylem by dismantling vessel pit membranes, the components of which are substrates for Xf’s cell wall-degrading enzymes (CWDEs). Xf utilizes at least one polygalacturonase (PG) and one endoglucanase (EGase) to breach pit membranes that separate one xylem vessel element from another. We have assessed the roles of two EGases in Xf in both their individual and collective roles in virulence and determined that these EGases act as additive virulence factors during the grapevine infection process. Furthermore, a proteomic analysis of the Xf secretome indicates that these two EGases are secreted via the Type II secretion system. Taken together, these data indicate that EGases are critical to the Xf infection dynamics in planta.