Invasive plant
Garlic mustard
Alliaria petiolata
Garlic mustard identification: a first-year rosette, a second-year flower stem and a garlic smell when a leaf is crushed.
State hub · PA
Pennsylvania
Invasive plants in Pennsylvania are listed in three noxious weed classes. Class B includes Japanese knotweed, tree of heaven and garlic mustard.
Last reviewed
Regulatory status
Pennsylvania's noxious weed list is set under the Controlled Plant and Noxious Weed Act (3 Pa.C.S. Chapter 15), which passed in 2017. The Department of Agriculture groups listed plants into Class A (established but geographically limited, intended for eradication), Class B (widely established, eradication not feasible) and Class C (not known to be present; the federal noxious weed list is included by default). Class B includes Japanese knotweed, tree of heaven, garlic mustard, poison hemlock, lesser celandine and Callery pear. Giant hogweed is Class A. Noxious weeds cannot be sold, transported, planted or otherwise propagated in Pennsylvania. The Act does not read as a blanket duty to clear existing plants, but the department can issue a control order requiring treatment for a specific site.
Pennsylvania’s current noxious weed list is set under the Controlled Plant and Noxious Weed Act (3 Pa.C.S. Chapter 15), which passed in 2017. It is not the same as the older 7 Pa. Code Chapter 110 list that still shows up in search results.
The Department of Agriculture puts listed plants into three classes.
| Class | What it means | Examples from the current list |
|---|---|---|
| Class A | Established in Pennsylvania but geographically limited; the state intends to eradicate it. | Giant hogweed, goatsrue, kudzu, Palmer amaranth |
| Class B | Widely established; the state says it cannot feasibly be eradicated. | Japanese knotweed, tree of heaven, garlic mustard, poison hemlock, lesser celandine, Callery pear, multiflora rose |
| Class C | Not known to be present; a potential threat if introduced. The federal noxious weed list is included by default. | Water soldier, plus the federal list |
Noxious weeds cannot be sold, transported, planted or otherwise propagated in Pennsylvania. That is the main legal effect for a homeowner who is buying, moving or planting a plant.
The Act does not read as a general order to clear every existing patch on private land. Its listed violation is sale, transport, planting and propagation. The Department of Agriculture can issue a control order that requires treatment for a specific site, so a letter from the department is different from a general listing. Penn State Extension puts it plainly: people who already have these plants are not required to remove them, but control is encouraged.
The older 7 Pa. Code Chapter 110 list is narrower. It names giant hogweed, multiflora rose, Canada thistle, musk thistle and Johnsongrass, among others, but it does not include the newer Class B additions such as Japanese knotweed, tree of heaven and garlic mustard. Use the department’s current class list when you need a plant’s legal status.
Three species are worth starting with in Pennsylvania: Japanese knotweed, tree of heaven and garlic mustard. All three are Class B. Our removal guides cover the methods. If you use an herbicide, follow the product label, because the label is the law.
Read the current Pennsylvania class list before you buy, move or plant a listed species. Browse all state pages. This page was checked against the state sources on November 3, 2026.
Reporting and official sources
- Pennsylvania controlled plant and noxious weed lists
- Pennsylvania Department of Agriculture, noxious weeds and controlled plants
Reporting routes and classifications change. Confirm the current process with the state agency before submitting a report.
Priority species in Pennsylvania
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Invasive plant
Japanese knotweed
Reynoutria japonica
Japanese knotweed identification: hollow jointed stems, squared leaf bases and deep rhizomes. It resembles bamboo but has herbaceous stems.
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Invasive plant
Tree of heaven
Ailanthus altissima
Tree of heaven identification: long compound leaves with smooth edges and a gland at each leaflet base, pale bark and a strong odor when crushed.
Sources
Facts on this page were checked against the sources below. Each link shows the date the source was accessed.
- Controlled Plant & Noxious Weeds Lists — Pennsylvania Department of Agriculture Accessed November 3, 2026
- Noxious Weeds and Controlled Plants — Pennsylvania Department of Agriculture Accessed November 3, 2026
- Temporary Order Establishing the Requirements for a Research Project on the Noxious Weed "Knotweed" — Pennsylvania Bulletin Accessed November 3, 2026
- 7 Pa. Code Chapter 110. Noxious Weeds — Pennsylvania Code Accessed November 3, 2026
- Pennsylvania's Newest Noxious Weeds — Penn State Extension Accessed November 3, 2026
Related pages
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All state pages
Browse every published state hub.
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Invasive plants
Identification profiles for invasive plants.