Frequently Asked Questions

Invasive plants are species that are not native to a specific location and have a tendency to spread, often causing damage to the environment, human economy, or human health. These plants can outcompete native vegetation, leading to a reduction in biodiversity and altering ecosystems.

By Executive Order 13751* (2016):

‘Invasive species’ means, with regard to a particular ecosystem, [emphasis added] a non-native organism whose introduction causes or is likely to cause economic or environmental harm, or harm to human, animal, or plant health.

*This amended Executive Order 13112 (1996).

• Rapid Growth and Reproduction: Invasive plants often grow quickly and reproduce in large numbers, allowing them to establish and spread rapidly in new environments.

• Adaptability: They can thrive in a wide range of environmental conditions, making them highly adaptable to different habitats.

• Lack of Natural Predators: In their new environment, invasive plants often face fewer predators or diseases that would naturally control their growth in their native habitats.

• Efficient Dispersal Mechanisms: These plants often have effective methods of spreading their seeds, such as wind, water, or animal transportation.

• Ecological Impact: Invasive plants can disrupt local ecosystems by competing with native species for resources such as light, water, and nutrients. This can lead to a decline or extinction of native plants and the animals that depend on them.

• Economic Impact: They can affect agriculture by reducing crop yields and increasing management costs. Invasive plants can also impact forestry, fisheries, and recreational areas, leading to financial losses.

• Health Impact: Some invasive plants can cause health problems for humans. For example, they might produce allergens or toxins that affect people or livestock.

• Kudzu (Pueraria montana): Originally introduced to the United States from Asia for erosion control, kudzu has spread extensively in the southeastern U.S., smothering native plants and trees.

• Japanese Knotweed (Fallopia japonica): Known for its ability to grow through concrete and asphalt, this plant can cause significant structural damage and is difficult to eradicate.

• Purple Loosestrife (Lythrum salicaria): This plant invades wetlands, replacing native plants and altering the habitat for wildlife.

The Virginia Department of Conservation and Recreation currently lists 103 plants as invasive in Virginia.

Many other non-native plants are being monitored for their invasive potential in Virginia. The list may be updated as new invasive species are identified.

Over 900 plants are collectively listed as invasive across one or more of the 50 states in the USA.

Japanese Knotweed (Reynoutria japonica) and Cogon Grass (Imperata cylindrica) rank at or near the top of the world’s worst invasive plants.

Japanese Knotweed can grow through lava, concrete, brick, asphalt. It can grow through the foundation of your house, and in the UK you may not be able to get a mortgage if Japanese Knotweed is found on your property.

Effective management of invasive plants involves a combination of prevention, early detection, and control methods. It is crucial to:

• Educate the Public: Raising awareness about the impacts of invasive plants and how to prevent their spread is essential.

• Implement Control Measures: These can include mechanical removal, chemical treatments, and biological control using natural predators.

• Restore Native Vegetation: After removing invasive plants, replanting native species can help restore the balance of the ecosystem and prevent future invasions.

Understanding and managing invasive plants is critical to preserving biodiversity and maintaining healthy ecosystems. By taking proactive measures, we can mitigate their impacts and protect our natural environments.

The best way to get a positive ID on a specific plant is to use a series of three tools.

First, use a good photo ID app on your phone — while no tool is perfect, many people find that PictureThis has the highest level of accuracy.

Once you have a potential ID from PictureThis, go to our ID & Control app to see if the plant is listed as invasive in Virginia. If you find the plant in our database, look at all the photos for comparison. Be sure to also check the native plant comparison photos provided, to confirm that you have the invasive plant and not a native look-alike.

Lastly, we recommend you visit the Digital Atlas of the Virginia Flora, or download the Flora of Virginia app on your phone, and read the listing for your plant. Check that the location where you found the plant is a match for the known places where these plants are likely to grow. This will help you confirm a positive ID.

There are several methods for controlling invasive plants. These include:

• manual methods (hand pulling, etc.)

• mechanical methods (mowing, sawing, etc.)

• chemical methods (cut stump, hack & squirt, foliar spray, etc.)

We have a Fact Sheet that describes each of these methods for you.

You can search for a specific invasive plant on our ID & Control app, and there you will find listed the various methods of control that have been found to be effective for that species.

The most effective timing varies by species. You can find general recommendations on the Virginia Department of Forestry control chart.

You can find more specific recommendations on Blue Ridge PRISM’s Management Calendar (coming soon!).

Winter is an ideal time to treat and/or remove many species of invasive plants in Virginia.

Woody species like trees, shrubs, and vines are often more easily accessible during the winter because the other vegetation has died back.

This is also a good time because there is less risk of damaging native plants that have gone dormant for the season.

For many invasive shrubs and vines, we recommend waiting for a warm winter day after a good, soaking rain or snow melt. This is a great time to get outside and work on removing invasive plants as the ground will be soft and many shrubs and vines can be pulled right out. Wineberry, Periwinkle, English Ivy, and Winter Creeper are just a few examples of invasive plants that are ideal for winter removal.

Many invasive plants can be controlled succesfully without using herbicides.

Some species — like Tree-of-heaven (Ailanthus altissima), for example — are extremely difficult to control without the careful use of a specific, highly targeted herbicide, and trying to manage these species without using herbicides may create an even worse infestation.

Prescribed fire has been an important land management tool for thousands of years, predating modern civilization.

Blue Ridge PRISM does not work with prescribed fire. However, you can find more information at the Virginia Prescribed Fire Council, including a list of fire contractors in Virginia.

Unfortunately, for most invasive plant species that are already established, the chances of eradicating them are very slim. For this reason, we talk about managing and controlling these plants, rather than eradicating them.

The exception to this is when a new invasive plant has just arrived in an area and there is only a small, isolated population. We call this period “Early Detection and Rapid Response,” or EDRR. This is when we need to move fast! If we act immediately, we have the best chance of eradicating this species before it can spread.

Learn more about the “invasion curve,” and why we all need to be vigilant in watching out for EDRR species.

An herbicide, also known as a weed killer, is a chemical substance used to kill or prevent the growth of weeds and other unwanted plants.

Herbicides are a specific class of pesticides and refer to those chemicals that kill plants.

“Pesticides” is the broad term and includes all materials that are used to prevent, destroy, repel, attract or reduce pest organisms.

The types of pesticides include:

• Insecticides: Kill or control insects

• Herbicides: Kill or control weeds

• Fungicides: Kill or control fungi

• Rodenticide: Kill or control rodents

Blue Ridge PRISM supports the safe and proper use of herbicides only when they are necessary. If there is a manual or mechanical method of treatment that will be successful, we will always recommend that.

Some plants, such as Tree-of-heaven (Ailanthus altissima), will respond to cutting or mowing with intensified vigor and will re-sprout from the stump or the roots —or both — and cause a bigger infestation than before. Without the use of herbicides these plants are extremely difficult to remove.

In other instances, the sheer size of the infestation may necessitate using herbicide. Japanese stiltgrass (Microstegium vimineum), for example, can be easily pulled by hand; however, when the forest floor is carpeted with acres and acres of stiltgrass, hand-pulling is not feasible. In this case, only a targeted foliar spray treatment will prevent this volume of stiltgrass from going to seed and spreading exponentially.

PRISM does not advocate for widespread, broadcast spraying of herbicides. Instead, the methods we recommend involve a highly targeted, surgical approach to help ensure that only the target invasive plant species is treated.

If you choose to use herbicides to control invasive plants, be cautious when using them. Read and understand the herbicide label prior to use. Use the correct amount and the correct concentration at the correct time.

You’ll find recommendations for specific plants on the Virginia Department of Forestry chart here, and also in our Invasive Plant ID & Control app.

The label is the law. If you are using herbicides in an aquatic environment, you are required to use an aquatic-safe herbicide.

As a practical matter, you may choose to only purchase aquatic-safe formulations when they are available.

You will find a list of personal protective equipment and other equipment here.

A “buckthorn blaster” is an inexpensive dauber bottle with a sponge tip. It resembles a bingo marker.

Buckthorn blasters are used for the highly targeted cut stump method of treating invasive woody shrubs and vines.

You can purchase one here.

The label is the law and you’ll find the list of required PPE on each herbicide label.

At a minimum, you can expect to need long sleeves, long pants, boots or closed-toe shoes, gloves, safety glasses, and a hat.

If you are mixing herbicides, you will also need long chemical-resistant gauntlet gloves that protect you up to your elbows, and a face shield. We recommend wearing an N-95 mask under the face shield as well.

You can find links to several herbicides, tools, and supplies here.

PRISM has created this online file for you and we’ll do our best to keep it updated. Let us know if a link is broken and we’ll get it fixed!

Remember, the label is the law. Using an herbicide for a purpose not specified on the product label is against the law.

The “Roundup” brand has many different products under this name and some have different chemical compositions. Some versions of Roundup have recently been reformulated and contain different active ingredients than before, so it is impossible to answer this question categorically.

Always read the label to determine what species of plants the herbicide is approved to treat.

We do not recommend using vinegar or mixtures of vinegar, salt, and dish soap. These will burn the above-ground portion of the plants, but invasive plants that have deep roots will grow back. Using these mixes will also kill all the beneficial insects and microbes in the soil.

PRISM does not recommend using agricultural vinegar.

Agricultural vinegar is sometimes used on weedy grasses or forbs. It is an extremely strong acetic acid and must be handled with caution and the proper PPE.

Agricultural vinegar works with sunlight to burn the tops of the plants. For shallow-rooted forbs, it may succeed in killing them. Deeply-rooted plants or plants with a tap root, however, may grow back from the roots.

Agricultural vinegar will also burn and kill insects, including pollinators, and microbes that it comes in contact with.

The label is the law. Each product label will have this information for the specific chemical. Please read the label carefully.

Herbicides can kill pollinators. PRISM recommends that you only use herbicides when the invasive plant is not in bloom, or after the flowers have faded, so the plant is not attracting any pollinating insects.

“Glyphosate degradation is a mainly microbial-mediated process [29,30], and the pathway has been widely studied in laboratories [31]. It degrades at a relatively rapid rate in most soils, with half-life estimated between 7 and 60 days [12].”

Source: NIH National Library of Medicine

A surfactant is a substance that reduces the surface tension of a liquid, which increases its spreading and wetting properties. Surfactants are also known as surface-active agents.

Surfactants are a type of adjuvant.

A nonionic surfactant is a type of surfactant (or adjuvant)that does not ionize, meaning it doesn't form charged species. Nonionic surfactants are often used in laundry and dishwashing detergents because they are low foaming and not significantly affected by water hardness.

Nonionic surfactants increase the efficiency of herbicides by helping the active ingredients diffuse into plant leaves.

A carrier oil for herbicide is an oil that helps herbicides penetrate the bark of trees, shrubs, or brush. Some examples of carrier oils include: 

• Basal oil: A safer, newer alternative to diesel fuel that's formulated to help herbicides penetrate bark. It's non-aromatic, non-carcinogenic, and has surface-active compounds. 

• Diesel fuel: A traditional carrier oil that can still be used, but newer options are safer. 

• Kerosene: A carrier oil that can be used for basal bark applications. 

• Fuel oils: A carrier oil that can be used for basal bark applications. 

• Methylated seed oil: A carrier oil that can be used for basal bark applications. 

• Crop oil: A carrier oil that can be used for basal bark applications. 

When using a carrier oil with an herbicide, it's important to read the herbicide's product label to make sure you're using the right carrier oil. You should also make sure to thoroughly mix oil-based herbicide mixtures. 

Blue landscape marker dye is not necessary, but it is extremely helpful when you are applying chemicals so that you can see where you have already worked.

We highly recommend using a marker dye. There are many brands available, and a small number of products come with the dye already mixed in.

If you need to purchase marker dye, you can buy one like this.

This dye is highly concentrated and you only need a VERY small amount.

Your property may qualify for one or more of the current state programs for landowners, depending on the location and type of invasive plant removal work you would like to do.

You’ll find all of the current programs that we know about listed here on the Virginia Invasive Plant Coalition website. Scroll down on the Resources page to the section labeled “Land Steward Assistance Programs.”

We will update this list as more opportunities become available.

Blue Ridge PRISM does not have funding to give grants for invasive plant removal.

The Plant Virginia Natives campaign produces beautiful native plant guides specific to each region of the state. Many of these guides are available to download for free.

Here are some great resources:

Lawns into Meadows

Prairie Up

The Virginia Native Plant Society maintains a list of vetted native plant nurseries in the state.

Chapters of VNPS also have annual native plant sales — follow your local chapter on social media or sign up for their newsletter for announcements of upcoming sales.