November in New England is not so fondly called stick season. It’s that short time between the panoramic color of fall leaves and beautiful deep snows. It can be a little quiet in the woods. So, on today’s hike I decided to survey the health of all the American Beech (Fagus grandifolia) trees I encountered. My results were dismal. Only one tree was free of beech bark disease.
Beech bark disease is caused by a unique relationship between an introduced insect called the Beech Bark Scale (Cryptococcus fagisuga), and Nectria fungi (Nectria coccinea var. faginata and N. galligena). This disease has been known in Europe since at least the 1840s, where it attacks European Beech (F. sylvatica). It was accidentally introduced to North American at Halifax, Nova Scotia in 1890 on a shipment of ornamental trees.
The infestation spreads about 10 miles per year, mainly from the dispersal of Beech Bark Scale by wind and animals. It first appeared in New England in 1929 when it was found in Maine. By 1950 it was found throughout the entire state, and by 1960 it was found across New England. Today it is as far west as Wisconsin and south into North Carolina and Tennessee.
Since there are few natural controls known, the disease is likely to become established across the entire range of American Beech. The native Twice-stabbed Ladybird Beetle (Chilocorus stigma), aptly named for the two bright red spots on each side of its black back, preys on Beech Bark Scale, but doesn’t appear to limit the population very much.
Beech Bark Scale is easy to see on infected trees in the fall. They exude small but noticeable white, waxy filaments on tree trunks. These wingless insects are parthenogenetic, egg growth and development occurs without fertilization by a male and all offspring are females. Adults lay eggs in the summer which soon hatch and the young nymphs, called crawlers, move into bark fissures or may be carried to other trees by wind or wildlife. Once the young crawlers settle down they push their stylet, a sharp needle-like mouthpart, into the bark and begin feeding and secreting the woolly wax cover that they use to help survive the winter season.
The minute wounds created by the stylets allow Nectria fungi to colonize. The fungal colonies cause cankers on the bark surface. This quickly leads to wilting of leaves and loss of twigs and branches. Eventually, the cankers cause enough damage around the tree that the trunk simply snaps in a wind storm. Beech snap is now common throughout the New England forest.
This is bad news for the wildlife that depends on beech for survival. Bear, deer and turkey rely on the energy rich beech nuts in the fall. The Early Hairstreak (Erora laeta), a tiny blue butterfly who’s caterpillars only feed on beech flowers, is only found in beech forests. There is at least a glimmer of hope. Some resistant trees have been found and are now being produced in nurseries with the hope that they could be transplanted throughout the range to perhaps bring healthy beech slowly back to the forest.
American Beech (Fagus grandifolia) trees I encountered. My results were dismal. Only one tree was free of beech bark disease.