Allegheny River Headwaters Watershed Conservation Plan

Allegheny River Headwaters Conservation Plan
Chapter 4. Biological Resources
most effective when applied late in the season, while the plants are preparing for dormancy. However, an
initial treatment mid-summer along with the late treatment would be effective to reduce the amount of
seeds being produced.
Spotted Knapweed
Accidentally introduced to the U.S. in the late 1800s as a contaminant in seeds and discarded soil
from ship ballasts, spotted knapweed has been established in McKean and Potter counties. This shortlived,
perennial, herbaceous plant derived its name from spots that are formed by black margin on the
flower’s bract tips.
Spotted knapweed forms a basal rosette of leaves during its first year, and then blooms in subsequent
years, typically for three to seven years. It has a deep and stout taproot that allows it to draw in water
from deep in the soil during dry conditions. The flowering stems reach eight to 50 inches tall and contain
25–35 purple-to-pink flowers per head. Each year—between June and October—the plant produces 500–
4,000 seeds per square foot and the seeds remain viable in soil for five to eight years. Seeds are dispersed
via humans, wildlife, livestock, vehicles, fill dirt, crop seed, and contaminated hay.
Spotted knapweed infests natural and semi-natural habitats, including barrens, fields, forest, prairies,
meadows, pastures, and rangeland. In addition to outcompeting native species, it reduces native plant and
animal biodiversity, decreases foliage production, and increases erosion, surface runoff, and stream
sedimentation. It prefers to establish in well-drained, light-textured soils that received summer rainfall.
However, it does not compete well with vigorously growing grasses in moist areas.
Manual, biological, and chemical treatments can be used to combat spotted knapweed populations;
combining these efforts increases the effectiveness of their use. Persistent hand pulling of the species
prior to seed set is effective when the entire crown and taproot is removed. Two larvae, three moth
species, and a weevil are natural predators of spotted knapweed, and when introduced into large
infestations, they can reduce seed production by half. A variety of herbicides are also available treatment
options; however, each one has advantages and disadvantages. Before using any treatment method,
determine which method is the best for the infested site and consider a combination of treatment methods.
Animals
Invasive animal species include forest pests, such as gypsy moth, Sirex woodwasp, and common
pine shoot beetle, as well as the aquatic spiny water flea. Information regarding invasive animal species is
not as readily available and numerous as that for invasive plant species. The section below details the
known invasive animal species.
Common pine shoot beetle
Native to Europe, the common pine shoot beetle was accidentally introduced into the U.S. from
infested packaging materials in 1992. This invasive beetle impacts pine trees by breeding under the bark
at the base of the trees. The entire State of Pennsylvania remains in a quarantined area, restricting the
movement of pine materials in order to prevent further infestation of the species.
The adult beetles range in size from three to five millimeters long, are brown or black and
cylindrical. The larva is approximately five millimeters long, with a white, legless body and brown head.
In March and April, the adult beetles become active, leaving their over-wintering sites in order to
mate and lay eggs in dying or stressed pine trees, freshly cut trees, stumps, logs, and bark mulch. The
adult females deposit their eggs into gallery systems bored approximately 10–25 centimeters long
between the inner bark and outer sapwood of the host. From April to June, the larvae feed and mature
under the pine bark in separate feeding galleries. When matured, they stop feeding, pupate, and tunnel
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