Masters Theses

Date of Award

12-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Paris Lambdin, Mark Windham, M. L. Pan

Abstract

American beech, Fagus grandifolia Ehrhart, is a dominant species in cove hardwood, northern hardwood and hemlock forests. Beech bark disease (BED), which can cause mortality of American beech, is a complex which includes beech scale, Cryptococcus fagisuga Lindinger, and the fungi Nectria galligena Bresadola and N. coccinea var. faginata Lohman, Watson, and Ayers. Beech scale was accidentally introduced into North America from Europe on stocks of European beech, Fagus sylvatica Linnaeus, in the 1890s. In 1993, beech scale and Nectria spp. were discovered in beech stands in the Great Smoky Mountains National Park (GSMNP). A research project was conducted to: 1) monitor incidence, progression, and impact of beech scale and BED in the GSMNP (project initiated in spring 1994 by other cooperators), 2) assess the incidence and seasonality of predatory mites in selected plots in the GSMNP, and 3) investigate areas outside of the GSMNP for the presence of beech scale.

Beech scale is currently present in all ten plots evaluated in the GSMNP. At Gregory Bald, the last plot to become infested, percent infestation reached about 25% in spring 1997. The percent of live trees within all plots infested with beech scale increased significantly from 55.6% in spring 1994, to 87.9% in spring 1997. Percent incidence of Nectria spp. has fluctuated, peaking at 19.6% in spring 1995 and decreasing to about 10% in spring 1997. The percent mortality of all trees within plots (n=455) has increased significantly from the initial value of 16.0% in spring of 1994 to 26.7% in spring of 1997. Forney Ridge exhibited the highest percent mortality of any single plot, reaching 90.9% of American beech dead in the plot by spring 1997. These data suggest that beech scale can be expected to continue to increase through areas once free from this pest and become increasingly vulnerable to infection by Nectria spp. As incidence of infection by Nectria spp. increases, beech mortality should also be expected to increase.

A new species of mite, in the genus Allothrombium, was observed to feed on scale. Populations of this predatory mite were monitored during the spring and summer of 1996 and 1997. While Allothrombium new sp. feeds consistently on beech scale, the presence of beech scale did not significantly effect the presence of mites on beech trees. Factors such as temperature, time of day, and time of year were significant influences on mite presence. The first-instar, of which most species of this genus are parasitic on arthropods, is inactive. The observations during spring and summer of 1997 suggest that the mites overwinter as adults and have one generation each year.

Five areas outside of the GSMNP, four in Tennessee and one in North Carolina, were examined for the presence of beech scale. No beech scale was found outside of the GSMNP in the areas investigated. Nectria spp. were found on one tree, but this infection was not suspected to be associated with BED.

As the infestation of beech scale on beech trees increases, tree mortality is also expected to increase. The high tree mortality at Fomey Ridge is an example of the devastation that beech scale and BED can cause, and may be a prelude to what may happen in other areas of the GSMNP. Although Allothrombium sp. has been observed feeding on beech scale, further research needs to be conducted to evaluate its feasibility as a possible biological control agent of beech scale. This predator may help to slow the dispersal of beech scale and consequently the effects of BBD. While beech scale is presently not found in this area outside the GSMNP, research suggests that it is highly likely for beech scale to eventually spread to these areas. Continued monitoring of beech scale, both within the GSMNP and areas surrounding the GSMNP, is necessary to better understand, and perhaps eventually control, beech scale and BBD.

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