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Kudzu (Pueraria montana var. lobata)
Photo credit: Matthew Erb/Tree Pittsburgh
What is a noxious weed?
A noxious weed is a plant species that has been designated by a country, state, provincial, or national agricultural authority as one that is injurious to agricultural and/or horticultural crops, natural habitats and/or ecosystems, and/or humans or livestock. Most noxious weeds are introduced species (non-native) and have been introduced into an ecosystem by ignorance, mismanagement, or accident. Occasionally some are native. Typically they are plants that grow aggressively, multiply quickly without natural controls (native herbivores, soil chemistry, etc.) and adversely affect native habitats, croplands, and/or are injurious to humans, native fauna, and livestock through contact or ingestion.
Noxious weeds are a large problem in many parts of the world, greatly affecting areas of agriculture, forest management, nature preserves and parks, and other open space lands. These weeds are typically agricultural pests, though many also have impacts on natural areas. Many noxious weeds have come to new regions and countries through contaminated shipments of feed and crop seeds or intentional introductions such as ornamental plants for horticultural use.
Which species are considered noxious in Pennsylvania?
In Pennsylvania, 20 plant species are considered to be noxious weeds (14 of which are tracked in the Pennsylvania iMapInvasives database). These species are determined to be noxious by the Pennsylvania Controlled Plant and Noxious Weed Act (2017) and are broken into Class A and Class B species.
Class A Noxious Weeds
Preventing new infestations and eradicating existing infestations of noxious weeds in this class is high priority. The following are Class A noxious weeds:
Palmer amaranth (Amaranthus palmeri)
Common water-hemp (Amaranthus rudis)
Tall water-hemp (Amaranthus tuberculatus)
Animated oat (Avena sterilis)
Dodder (Cuscuta spp.) - except for native species
Goatsrue (Galega officinalis)
Broomrape (Orobanche spp.) - except for native species
Class B Noxious Weeds
The department may require control of Class B weeds to contain an injurious infestation, or may provide education or technical consultation. The following are Class B noxious weeds:
Exotic Lythrum species, including Lythrum salicaria L. (commonly known as purple loosestrife), the Lythrum salicaria complex and Lythrum virgatum L. (commonly known as European wand loosestrife), their cultivars and any combination thereof.
Goatsure (Galega officinalis)
Photo credit: Sarah Gregg/Flickr
Hydrilla - Federal Noxious Weed (Gallery)
Hydrilla (Hydrilla verticillata)
Photo credit: Robert Vidéki, Doronicum Kft., Bugwood.org
Which species are considered federal noxious weeds?
Over 100 species have been designated as federal noxious weeds based on their invasive characteristics, according to the United States Department of Agriculture (USDA). View a complete list of federal noxious weeds here. From this list, the following federal noxious weeds are currently being tracked in the Pennsylvania iMapInvasives database and are listed under the following two categories:
Early Detection Species
Saw-petal water-hyacinth (Eichhornia azurea)
Indian swampweed (Hygrophila polysperma)
Giant salvinia (Salvinia molesta)
Tropical soda-apple (Solanum viarum)
High Priority Species
Giant hogweed (Heracleum mantegazzianum) - Also PA noxious weed
Goatsrue (Galega officinalis) - Also PA noxious weed
Hydrilla (Hydrilla verticillata) - Also PA noxious weed
Who should I contact if I find a noxious weed?
If you believe you've discovered a noxious weed, please report your finding(s) to:
Trilby Libhart, State Botanist
Pennsylvania Department of Agriculture, Bureau of Plant Industry
Address: 2301 North Cameron Street, Harrisburg, PA 17110
Pennsylvania Extension Service
Find your local county extension office.
Submit a Public Report (for non-registered users)
Submit an Observation Record (for registered users)
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Purple loosestrife (Lythrum salicaria)
Photo credit: © Ellie Buick/Flickr
Feral swine (Sus scrofa)
Photo credit: Brian Gratwicke, Flickr Creative Commons
Excluding noxious weeds, are there other species of concern to be mindful of?
Yes. In Pennsylvania, there are many species that present serious concerns based on their invasive characteristics. These species are broken down into two categories: Early Detection & High Priority.
Early Detection species are defined by any of the following criteria:
1. Species that are newly established in Pennsylvania.
2. Species that are thought to be in Pennsylvania but are not well documented.
3. Species that are expected to arrive in Pennsylvania (based on professional judgment) AND are thought to be at least moderately invasive.
View Pennsylvania's Early Detection species.
High Priority species are defined as being exotic, invasive species that are not yet widespread statewide (occurring in less than 1/3 of Pennsylvania counties), AND are considered at least moderately invasive.
View Pennsylvania's High Priority species.
Other than the Pennsylvania Department of Agriculture, do any of Pennsylvania's state agencies have particular species they are concerned about?
The Pennsylvania Fish and Boat Commission (PFBC) currently has a list of banned aquatic invasive species (AIS) which are not allowed to be sold, bartered, possessed, or transported in Pennsylvania. View PFBC's banned AIS list.
The Pennsylvania Department of Conservation and Natural Resources (DCNR) has information on their website regarding various invasive species currently threatening our natural lands. View details on those species.
The Pennsylvania Game Commission (PGC) is currently monitoring feral swine (Sus scrofa) in our state due to its devastating effects to our natural wildlife and habitats as well as many commercial industries. Learn more about the negative impacts of feral swine:
Rusty crayfish (Orconectes rusticus)
Photo credit: U.S. Geological Survey, Bugwood.org
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