Leaves in the upper portion of the crown may remain attached. Leaf symptoms usually include brown spots or patches that expand outward to the leaf margins. Although the leaves may be curled and distorted, they usually do not wilt. In the case of oak decline these factors can include drought, defoliation, fungi that cause stem cankers or root diseases, and wood-boring beetles. The interaction of these factors may result in the decline and death of oak trees over a local or regional area.
Symptoms vary greatly, and differentiating oak decline from oak wilt can be quite difficult.
The absence of the typical leaf symptoms of oak wilt and the retention of dead leaves on the tree are indicators of oak decline. Trees killed by oak wilt are usually completely defoliated and retain few living or dead leaves, but this may not be a consistent symptom for red oaks in the South. Oak wilt usually occurs in discrete, spreading pockets of mortality, with trees on the margins of the infection center becoming infected over time. Declines may occur in discrete pockets, or over a fairly large area, but do not typically spread outward from an initial infection center. Trees in decline may die over a period of years, or may ultimately survive a decline episode with only dead branches in the crown.