University of Maryland Extension CMREC, HGIC, and the UMD Plant Diagnostic Lab have received numerous reports of sudden discoloration of foliage and death of white oak (Quercus alba) trees throughout the Mid-Atlantic region in August through October of 2019. We have visited sites with symptomatic trees, examined samples submitted to the UMD lab, and spoken with several arborists, landscapers, state and local forestry officials and landowners, in pursuit of information that might reveal a specific cause.
While our investigation is still in progress, here are some factors that these individual cases all have in common:
1. Affected trees are older trees, approximately 40 – 80 years old or older. Younger trees in the same areas are not affected.
2. The onset of symptoms is fast – foliage that appeared healthy in spring and summer, became brown in color in August, often within 2-4 weeks. Most of the brown leaves remain attached to twigs of affected trees.
3. Although other oak species have been showing twig dieback and decline symptoms for several years, it is primarily white oaks that have this sudden browning of the canopy.
4. Symptomatic white oaks are often in urban and suburban landscapes, but trees in forests and in large landscaped areas with unrestricted root zones are also affected.
5. In some cases, affected trees have large trunk wounds, previous root damage from compaction or construction, and show previous branch dieback, but many trees do not have any visible obvious symptoms of injury or major decline prior to browning of the foliage.
6. A variety of pests and diseases that are usually considered to be opportunistic invaders of stressed trees (such as ambrosia beetles, Armillaria root rot and Hypoxylon canker) are often observed in symptomatic trees. Sawdust-like frass at the base of the tree or on the bark of the lower trunk indicates the invasion of ambrosia beetles.