Other Introduced Insects and Diseases
While many insects and diseases were introduced more than 50 years ago, "new" introductions are still a threat. Seven species of bark beetles have been recorded in the Northeast for the first time in the past decade. Beech bark disease, already established in New England, New York and Pennsylvania, is slowly spreading toward Maryland.
The hemlock woolly adelgid, a native of Asia introduced into the United States in the 1950's, is a potentially serious pest of hemlock trees. This aphid-like insect is commonly found in urban forests around Baltimore and Washington, and is slowly spreading toward the native hemlock stands of western Maryland. Since 1991, forests with large numbers of hemlocks have been attacked by the hemlock woolly adelgid in Frederick County.
The pine shoot beetle (Tomicus piniperda), native to Europe and Asia, is attacking forests in six north central States. These States are currently under Federal quarantine. Quarantine procedures restrict the movement of pine Christmas trees, pine nursery stock, and pine logs unless they are inspected and certified as pest-free. A proposal to add pine wreaths and garland as regulated articles is under consideration.
In April, 1995, a single pine shoot beetle was found in Allegany County. Since the nearest known infestation is several hundred miles from Allegany County and only one beetle was found, quarantines have been delayed until a more extensive survey has been completed. However, the US Department of Agriculture intends to amend the pine shoot beetle quarantine to include Allegany County in the future.
Non-native plants established in Maryland are threatening forests and other native plant communities. Many of these plant species were introduced prior to the initiation of Federal plant quarantines in 1919. Other species have been introduced more recently for landscaping, wildlife habitat, or erosion control.
Favorable climate and soil conditions, and absence of competitors to keep them in check are allowing these introduced species to spread to menacing proportions. Control is often difficult and expensive. While not as obvious or dramatic as the damage caused by insects and diseases, introduced species can dominate forested areas and old fields or other openings, preventing tree regeneration, inhibiting native herbaceous plants, reducing visual quality, and reducing recreational use. For example, mile-a-minute (Tracaulon (Polygonum) perfol-iatum) can be found covering herbaceous plants, shrubs, and small trees. Some of the introduced plant species that are causing problems in Maryland are listed below.
Some of the introduced plant species and the region of the state where they are causing problems.