Beech bark disease has been causing mortality of American and European beech (Fagus grandifolia and Fagus sylvatica, respectively) trees since its discovery prior to 1849 in Europe, although until 1914 beech scale was solely being blamed. We now know that the cause is a combination of scale damage and fungal infection. Beech bark disease is caused when the bark is altered by the insect pest, beech scale (Cryptococcus fagisuga) leaving it weakened, open and susceptible to infection by the fungus Nectria coccinea var. faginata.
This combination of infestation followed by infection results in high initial mortality rates and surviving trees are left deformed and incredibly weakened. Without the damage from scale insects opportunity for infection from fungus is greatly diminished. Scientists at the U.S. Forest Service’s Northern Research Station are developing a technique to identify trees with higher disease resistance; artificially infesting healthy trees left among areas of heavy BBD impacts with scale eggs demonstrating that these trees were resistant to the scale portion of the disease complex.
The protocol they have developed can be used to evaluate trees for disease resistance in the field, as well as in smaller potted seedlings and even grafts. Identification of scale resistant specimens is a critical component of managing beech bark disease, improving programs and developing effective silvicultural manipulation techniques. Beech bark disease research thus far has focused on identification, propagation and retention of American beech trees with known resistance to beech scale insects. Deeper investigation into the genetics of these trees shows that resistance is a heritable trait, making careful selection and breeding of trees with this trait can produce significant improvement within the span of a single generation. State and national forest managers, empowered by these findings, have begun to establish regional orchards composed of resistant beech trees in order to foster a genetically diverse source of BBD-resistant seeds for restoration purposes. Additionally, removing susceptible trees and retaining resistant trees within a forest stand can result in vast improvements to health and vigor of current and future generations.
Research studies such as these provide positive outlooks for what could have been a bleak future for American beech stands and the ecosystems in which they reside. Methods devised from these results are effective and accessible to forest and natural resource managers. Perhaps research into disease resistance of other species susceptible to devastation from pests and disease will provide similar results and hope.
Koch, J.L., Carey, D.W. A Technique to Screen American Beech for Resistance to the Beech Scale Insect (Cryptococcus fagisuga Lind.). J.
Vis. Exp. (), e51515, doi:10.3791/51515 (2014)