Tree versus landscape-level effects: Can basal debarking slow the spread of oak wilt?

Oak wilt is a fungal disease (caused by Ceratocystis fagacearum) that infects trees in the white and red oaks groups. The disease is spread through root grafts and insect transmission of sporangia (fungal mats), which form only on red oaks. Texas red oak (Quercus buckleyi), an important component of breeding habitat for the endangered golden-cheeked warbler (Dendroica chrysoparia), is highly susceptible to the disease and dies rapidly after infection. In three pairs of plots (all > 60 ha), we tested whether two years (2004 and 2005) of basal debarking, a recommended treatment for infected red oaks, would reduce fungal mats formation and slow disease spread. Control trees were 4.6 times as likely as treated trees to form fungal mats. Furthermore, basal debarking reduced the number of fungal mats on trees with at least one fungal mat (4.8±0.2 vs. 2.8±0.3; p=0.03). However, these reductions did not influence landscape-level infection rates. In 2005, infection rates increased in two of three control plots and in two of three treatment plots. In 2006, preliminary data indicate that the number of infected trees decreased in two study areas (both control and treatment plots). We suspect that weather may control the appearance of symptoms: hot, dry summers stress the fungus, which is at the southern edge of its range in Texas. Furthermore, disease spread through root grafts, which is not affected by our treatment, may be more prevalent than insect-mediated spread. Basal debarking alone is not an effective treatment for oak wilt in the Edwards Plateau.