In addition to oak wilt, there are several tree health conditions caused by extreme environmental conditions (e.g. drought), Hypoxalon canker (non-aggressive, facultative saprophyte, Hypoxylon atropunctatum), oak decline (complex interaction of natural and human-caused environmental stresses and pests that weaken oaks over time), climate change and other stressors which may affect habitat quality in Hays County.
Oak wilt is caused by the fungus Ceratocystis fagacearum which develops in the outer sapwood in vessels or tissues that conduct water and nutrients from the roots to the leaves (Appel 2001a), is infectious and potentially affects all Quercus and related species in the family Fagaceae. Quercus species vary in resistance or vulnerability. Foliar symptoms (unseasonal defoliation, coloration), patterns of tree mortality (large clusters, unseasonal die off), and the presence of fungal mats are indicators of oak wilt.