Oak Mortality in Pennsylvania: A Ten-Year Study

Abstract

Abstract The primary cause of crown dieback and mortality in the red oak group (Quercus rubra L., Q. coccinea Muenchh., and Q. velutina Lam.) was determined to be insect and spring-frost defoliations. An oak leaf tier (Croesia semipurpurana [Kearf.]) was the most important agent, due to its selective feeding habits within this group. Other environmental, site, and pathogenic factors contributed occasionally to deterioration but did not initiate the decline process. Mortality ceased and recovery of declining oaks began when defoliation ceased, in spite of the most extended period of drought on record. Two or three consecutive years of 60 percent to 100 percent defoliation predisposed trees, or crown portions, to killing attacks by the two-lined chestnut borer (Agrilus bilineatus [Web.]). Pure stands of the red oak group suffered the greatest losses and should be avoided in silvicultural management. Mortality of chestnut oak (Q. prinus L.) and associated white oak (Q. alba L.) was due principally to continuous attacks of a pit-making oak scale (Asterolecanium minus [Ratz.]).