Invasive plants along our roadsides, in our natural areas, or on our own properties destroy natural habitats. Great hulks of intertwining vines hide the identify of trees and shrubs. Hikers are impeded by stands of thorny, vine-wrapped, impenetrable thickets. Homeowners are now fighting the invasions of stiltgrass and wavyleaf grass in their lawns. Eradicating invasive plants can be a discouraging, costly, time- and labor-intensive battle. All these nonnative invasive plants share a fearsome ability to reproduce prolifically and outcompete native plants. The changes they impose threaten the existence of insects, birds, and wildlife.
This treatment calendar is based on data compiled by Blue Ridge PRISM (Partnership for Regional Invasive Species Management, Inc.). This volunteer-driven, nonprofit organization is dedicated to reducing the negative impact of invasive plants in the northern Blue Ridge Mountains of Virginia. For more information about the history of the organization, its mission, and the services it provides, see Blue Ridge PRISM.
Many of these nonnative plants will be familiar to you; some are not. Many are still sold in the trade by nurseries and plant purveyors because they are deemed to have ornamental beauty. But don’t let appearances deceive. These plants are a scourge whose rippling effects will pass from one decade to the next. For a brief discussion of the legislative process for controlling invasive plants, see “Don’t Buy Nonnative Invasive Plants – Even If You Can.”
The goal of this calendar is to provide an easy reference for identifying WHEN to treat WHICH invasive. This goal is complicated by the fact that there are often multiple types of treatments recommended for each invasive depending on several factors: the time of the year, the area in which the invasive grows, and the stage of plant maturity. This means that many invasives can be treated at different times of the year and will appear in more than one control month.
The following examples illustrate how control methods are influenced by multiple factors:
- When plants are small, manually pull in the spring when the soil is moist and there is a better chance of getting ALL the root fragments. Many invasives resprout if even a small piece of their roots is left in the ground. Manual methods are a good choice for smaller, newer infestations when the soil is moist.
- Larger plants may not respond well to manual pulling because it is more difficult to get all their root fragments. They either can’t be pulled at all, or you risk leaving the remaining roots in the ground to regrow.
- Tree stump methods, including cut stump (followed immediately by an herbicide application to the cut), hack and squirt, and basal bark can be done anytime of the year EXCEPT during leaf out when the sap is flowing upward to the new leaves. When sap is flowing upward, the herbicide won’t be readily absorbed by the roots.
- When using the hack and squirt technique, slow deterioration from the herbicide might create a falling hazard in high traffic areas. In this case, cut the tree down and treat the stump with herbicide.
- Fall to late winter (October-February) is usually considered a particularly good time for tree stump eradication methods because the plants will be easier to access without heavy undergrowth, and the temperatures are cooler.
- Foliar treatments (applying herbicide to leaves) are always effective for woody evergreen invasives such as English ivy, wintercreeper, and vinca. Foliar treatments are also usually effective for deciduous plants after they have leafed out and until leaf drop in the fall.
- If a foliar treatment is recommended, avoid damage to native plants that are in proximity, and use aquatic-compatible herbicides near water sources.
This calendar summarizes the information provided in the PRISM fact sheets; please refer to these Fact Sheets for more in-depth information on plant characteristics, environmental impact, and multiple treatment options. To see the PRISM Fact Sheets on each plant and photos for identification, click on the link highlighted in the plant’s name. For a description of different control methods, see Blue Ridge PRISM/Fact Sheets/Control Methods. For types and amounts of the recommended herbicides, Blue Ridge PRISM refers to Va. Dept. Forestry/Non-Native Invasive Plant Species Control Treatments.
NOTE ON HERBICIDES: THE LABEL IS THE LAW. READ THE LABEL. Carefully prepare and apply herbicides according to label directions; apply the minimum amount of recommended herbicide that will be effective for a particular situation. Be aware that the labels can change; refer to labels for updated information.
We would all like to avoid herbicides, but these invasives are so prolific and so persistent, that herbicides are often necessary. To minimize the use of herbicides, use a paintbrush approach or a spot application whenever possible rather than a foliar spray. If a foliar spray is the most effective method, woody shrubs can be cut back first to minimize the amount of herbicide that’s needed. When using the cut stump method for larger diameter trunks and vines, herbicide can be painted 1″ around the inside perimeter of the cut stump rather than on the entire surface. This VIDEO demonstrates how to use a paintbrush approach with the cut stump method. Be aware that cut stump, hack and squirt, and basal bark treatments require a much higher concentration of an herbicide’s active ingredient (a.i.) than any foliar spray. Using foliar spray concentrations for cut stump, etc. will be ineffective. See this Blue Ridge PRISM article for instructions on how to safely and effectively use herbicides.
INVASIVE WATCH BY MONTH
FEBRUARY
Paradise Tree or Tree of Heaven (Ailanthus altissima) is a nonnative invasive that threatens natural areas, agricultural fields, disturbed areas, and developed landscapes. Ailanthus is a particularly important target plant because the nonnative insect pest, Spotted Lanternfly, prefers, and may even require, A. altissima trees to complete its lifecycle. A spotted lanternfly infestation has the potential to severely damage Virginia’s orchard crops and canopy trees. Small ailanthus saplings, up to about 3’, can usually be hand pulled or foliar sprayed. If the stem is too big to hand pull, try breaking it with your hands. The wood is very brittle and breaks easily. Apply concentrated herbicide to the end of the broken stem. This can be done all year, except during leaf out. If the stem is too thick to break, use the cut stump technique applying herbicide immediately to the cut. The basal bark treatment can be used for trees with 4-6” stems. The hack and squirt technique can be used on stems that are 4” in diameter up to mature trees. Do not use the hack and squirt method if the tree is situated in a high-traffic area; deterioration from the herbicide over time might create a hazard once the tree falls. NOTE: If you are not using herbicide and the tree is too big to hand pull, LEAVE IT ALONE. Without applying herbicide, ailanthus will initiate its survival response and generate dozens of root sprouts worsening the infestation.
Lesser Celandine or Fig Buttercup (Ficaria verna, previously named Ranunculus ficaria) grows so densely and so rapidly that it forms a continuous thick mat of foliage that smothers low perennials and prevents the seed of wildflowers, grasses, and trees from germinating. A member of the buttercup family, this plant has toxic properties that can cause illness in livestock. The foliage sprouts from underground roots and tubers and appears in late winter before anything else greens up. Flowers begin blooming in March or early April and stop when the weather becomes hot. When blooming finishes, the leaves yellow and the plants go dormant. Small infestations of lesser celandine can be controlled by hand digging when the soil is moist. Care must be taken to remove as much of the plant material (including all root material, bulblets and tubers) as possible. For larger infestations, apply foliar applications of herbicide to lesser celandine during the late winter through the early spring (February-March) before native plants emerge. Lesser celandine is usually found growing close to water; in this case, use an aquatic-approved glyphosate applied at a rate of 1.5%-2.0%. Despite its invasive properties, F. verna is still commercially sold by nurseries and plant purveyors.
MARCH
Asiatic or Oriental Bittersweet (Celastrus orbiculatus) is a branched, deciduous vine with woody stems that can scale trees up to 60’ high. Stems of old vines are commonly 4” in diameter. Be careful with identification; Asiatic bittersweet closely resembles American bittersweet (Celastrus scandens), a relatively rare native. In fall, the fruits turn red and remain in winter when they are eaten by birds and dispersed to other locations. Hand pull small vines in spring when the soil is moist. Be sure to remove the crown and all large roots or vigorous new growth will occur. Low bushy vines or resprouted vines can be killed with a foliar herbicide spray after leaves appear in spring through fall. Be mindful of native plants growing in the area. It is best not to spray large vines. From fall to winter, use the cut stump method with herbicide applied immediately to the cut or use the hack and squirt method when vines are large enough.
Garlic Mustard (Alliaria petiolata) has displaced native wildflowers such as spring beauty, wild ginger, bloodroot, trillium, and toothworts in many forested areas. Although this plant is easiest to recognize after it produces white flowers in early April, its foliage is also distinctive, and all parts of the plant emit a strong garlic odor. It is easy to pull in spring when the ground is moist. If the infestation is too large for hand pulling, spot-spray the rosettes with a recommended herbicide any time the ground is not frozen. It is essential to remove garlic mustard before it sets seed in May-September.
Mile-a-Minute (Persicaria perfoliata) is an annual vine and prolific seeder that can grow 6” a day and reach heights of 25’ in a single season. Tiny, recurved, needle-sharp barbs arm its leaves and stems. Clusters of tiny, white flowers appear in June followed by green fruits that ripen to bright blue. Seeds of green fruits are viable. The plant flowers and fruits continually from early summer until frost. Seeds of mile -a-minute can float for days, allowing the noxious weed to rapidly invade an entire watershed. Mile-a-minute can be manually pulled before it sets seed but wear gloves to protect against the barbs. Foliar sprays are effective but also kill whatever is underneath the vine. A preemergent herbicide is called for in large areas of infestation. The herbicide should be applied to the soil in early to mid-March before seeds germinate in June. Do not use preemergent herbicides near wetlands, streams, etc. because it harms aquatic life.
APRIL
Callery or Bradford Pear (Pyrus calleryana ‘Bradford’) and other ornamental pears started out as popular landscape trees in the 1960s and are now considered invasive in 29 states. Control trees less than 6’ tall with a higher-than-usual (3-4%) concentration of foliar spray. Foliar sprays are effective from when leaves emerge in spring until just before they begin to develop fall color. Use the standard approaches for eradicating invasive trees: hand pull small saplings; if too big to pull, use the cut stump method with herbicide applied immediately to the cut; the basal bark treatment; or hack and squirt. You can hand pull any time and use the other approaches any time except at leaf out.
Wavyleaf Grass (Oplismenus undulatifolius) has now invaded Virginia and appears on the state’s noxious weed list. It thrives in shady sites from very moist to somewhat dry, and spreads through root-like stems called stolons. The wavy leaves have the appearance of corrugated cardboard or water ripples. Pointed seed tips (awls) spread for miles by grabbing onto the fur of animals and the clothes of hunters and hikers. This perennial grass breaks dormancy and starts growing rapidly in April. Seeds germinate from April into June. Wavyleaf can be hand pulled if populations are small, but all bits and pieces of stolons must be removed or they will resprout. Be sure to remove tiny seedlings which resemble miniature, mature plants. For larger infestations, two herbicide treatments during the same growing season are strongly recommended. Use a recommended grass-specific herbicide from April through June. This herbicide won’t harm wildflowers. After June, use a non-selective herbicide; some studies have shown that grass-specific herbicides are less effective in the summer. Non-specific herbicides may also be used from April until frost, but other plants will be at risk. In wet areas or near streams, use an aquatic-safe product. You must complete the control treatment before wavyleaf begins setting seed in late summer.
MAY
Garlic Mustard (Alliaria petiolata), generally described in the March treatment section, sets seed in May-September. It is essential to remove garlic mustard before it sets seed. Do not mow garlic mustard when seed pods are present in May-September.
Kudzu (Pueraria montana var. lobata) has engulfed at least 7 million acres of public and private land in the Southeast. It is easiest to spot kudzu when its very showy reddish-purple flowers appear in late summer to early fall. Foliar herbicide sprays must be applied twice a year. The first spray is applied in late spring or early summer after leaves mature. The second treatment is applied in late summer or early fall. New (small) outbreaks can be controlled without herbicide by grubbing (pulling out by the roots) any time of year.
JUNE
Autumn Olive (Elaeagnus umbellata) targets sunny fields and pastures, roadsides, forest edges near mowed fields, and open woods. Its silvery green leaves appear early in spring and last until late fall. Red, oval fruits ripen in August and September. Seedlings and young autumn olive shrubs can be hand–pulled or dug when the soil is moist if the population is not extensive. Digging larger plants is problematic because they resprout from any roots left behind. For larger and/or mature stands, prevent seed production and dispersal by cutting back and treating plants with herbicide by mid-July to prevent seed ripening. Autumn olive can be controlled at any time of year, except during leaf out (spring growth), by cut stump with herbicides or hack and squirt for large stems. Watch for resprouts; cut and treat new stems or apply a foliar herbicide spray to the new foliage. The basal bark method can also be used with a concentrated herbicide in a horticultural oil. This is most effective in January-February or from May-October. Foliar sprays can be used from spring through fall but may need a second application and may not be effective. This is a very difficult plant to eradicate. See the PRISM Factsheet for more detail.
Mile-A-Minute Vine (Persicaria perfoliata, formerly Polygonum perfoliatum), included in the March treatment section, begins to flower in June with clusters of tiny, white flowers followed by green fruits that ripen to bright blue. The plant flowers and fruits continually from early summer until frost. Both manual pulling and herbicide treatments should be done before seed setting in mid- to late-June.
Multiflora Rose (Rosa multiflora) is a multi-stemmed, spreading shrub with branched, thorny arching stems (canes) that can climb high into trees. Multiflora rose forms dense thickets by three methods: rooting at the tips of its long, arching canes; forming new crowns and canes from its spreading root system; and producing abundant fruits. White, yellow-centered flowers bloom in May and June, followed by small, hard, green fruits (rosehips) in mid-summer. It is best to control this invasive before rosehips ripen to red in fall. Several control methods will be necessary over several years. Pulling or grubbing (remove by the roots) individual shrubby plants from the soil works only if all roots are removed. Mow or weed whack the shrubs (using a brush cutter, not a string trimmer) and apply a foliar spray to the regrowth. You can also use a cut stump method on the shrub with an immediate application of herbicide to the cut. For vines that climb into trees, cut the stems close to ground level and paint or spray an herbicide immediately on the cut vine stump. Do not confuse multiflora rose with native roses. Native roses have pink, not white, blossoms, as well as other different characteristics. Natives are rare and don’t form the extensive expanses that you find with multiflora rose.
Tree of Heaven or Paradise Tree (Ailanthus altissima), generally described in the February treatment section, can be treated with the hack and squirt stump method best done from June 1 to October 1.
JULY
Japanese Honeysuckle (Lonicera japonica) is a rapidly spreading nonnative vine that competes for both above- and below-ground resources, inhibiting the growth of desirable trees, shrubs, grasses, and wildflowers. This vine retains its leaves well into winter (year-round in mild climates). Hand pulling young Japanese honeysuckle in a small area when the soil is moist can be effective, but any roots left in the soil will resprout. Foliar sprays are less effective in spring because the herbicide does not thoroughly move from the leaves into the roots during spring growth. If feasible, wait until after July 4 to treat with foliar sprays. Don’t spray overhead vines. Instead, cut them near the soil any time of year to kill the top growth; apply foliar herbicide to the regrowth. For the cut stump method, sever thick vines near the ground and treat the cut ends with a recommended concentrated herbicide from early summer into winter.
Porcelain-Berry (Ampelopsis brevipedunculata) is a woody perennial that is related to grape and grows so fast that it can engulf a small tree, such as a dogwood, in one growing season. This invasive vine has a vast, hard-to-kill root system. Tiny, yellow-green, nectar-containing flowers are arranged in flat clusters and bloom June through August. They are followed by colorful clusters of shiny berries of different colors, including creamy-white, green, yellow, and lilac. These eventually ripen to bright turquoise blue in September and October. Gardeners continue to buy this plant because of its attractive berries. Herbicidal foliar treatment is most effective when applied between midsummer and early fall. For large infestations, foliar treatments are the only feasible option. To reduce the amount of herbicide needed, cut back the vines and spray the regrowth. Hand pulling works only for young plants. It is nearly impossible to dig up the taproot of an established porcelain-berry. To prevent seed dispersal, remove porcelain-berry by pulling, cutting, or mowing from winter to midsummer, before any fruits develop for that season.
Wavyleaf Grass (Oplismenus undulatifolius), described generally in the April treatment section, should be treated with two herbicidal foliar treatments within the same season. From April-June, use a grass-specific herbicide. After June, use a non-selective herbicide; some studies have shown that grass-specific herbicides are less effective in the summer. Be mindful, however, that non-selective herbicides will put other plants at risk. In wet areas or near streams, use an aquatic-safe product. Complete control treatments before wavyleaf begins setting seed in late summer. If pulling manually, get all parts of the stoloniferous roots.
AUGUST
Japanese Stiltgrass (Microstegium vimenium) forms a dense ground cover that smothers native plants and prevents regeneration of forests and fields. Hand pulling small infestations when the soil is moist before plants set seed is effective but labor intensive. Mowing is best done just before stiltgrass flowers in August and September and need be done only once if you wait until then. Mow stiltgrass as low as possible, scalping the ground, to remove all above-ground parts. Foliar sprays are effective, but the type of herbicide and the timing of application is important. See the PRISM Factsheets for more detailed information.
Kudzu (Pueraria montana var. lobata), generally described in the May treatment section, is easiest to spot when its reddish-purple flowers appear in late summer to early fall. Foliar herbicide sprays must be applied twice a year. The first spray is applied in late spring or early summer after leaves mature. The second foliar treatment is applied in late summer or early fall. Treatment using the cut stump followed by herbicide treatment is best done in late summer or early fall. New, small outbreaks can be controlled without herbicide by grubbing (pulling out by the roots) any time of year.
SEPTEMBER
Porcelain-Berry (Ampelopsis brevipedunculata), generally described in the July treatment section, is easy to spot in fall when clusters of different colored berries ripen to bright turquoise blue in September and October. Herbicidal foliar treatment is most effective when applied between midsummer and early fall. For large infestations, foliar treatment is the only feasible option. Cut stump bigger vines applying an herbicide immediately to the cut. If you can reach the largest stems in the tangle, use a basal bark application. Apply a concentrated, recommended herbicide mixed with horticultural oil to the lowest 12” of the stems; no cutting is needed. Be careful not to spray nearby desirable plants.
FALL / EARLY WINTER / WINTER (October- February)
Many invasive plants are easily identifiable in fall because of brightly colored berries, fall foliage color, or both. Although there are multiple treatment approaches that work at different times of the year, this section describes eradication methods that are effective from fall to late winter. These methods include cut stump, hack and squirt, and basal bark. The methods may be applied at any time of the year except for early spring when the sap starts flowing upward to the leaves.
Asiatic or Oriental Bittersweet (Celastrus orbiculatus), generally described in the March treatment section, is easy to spot from fall into winter due to its golden-colored foliage and brightly colored reddish berries. Tag in fall if you want to treat in the spring. It is best not to spray large vines; cut stump them from fall to winter and immediately apply herbicide or use the hack and squirt method. Hack and squirt is faster and easier than cutting.
Autumn Olive (Elaeagnus umbellata), generally described in the June treatment section, can be effectively treated in January-February with the basal bark method using a concentrated herbicide in a horticultural oil.
Callery or Bradford Pear (Pyrus calleryana ‘Bradford’), generally described in the April treatment section, can be treated from fall into early winter by using cut stump, hack and squirt, or basal bark methods.
Chinese Privet (Ligustrum sinense) is an evergreen to semi-evergreen shrub, growing 15-30’ tall, that can form large stands and impenetrable thickets. Although Chinese privet and all other species of privet are invasive, they are still being sold in nurseries as hedges or privacy screens. White or off-white flowers bloom profusely in June; blue-black, berrylike fruits appear in August and last into winter when they are eaten by birds and small mammals. Privet seedlings and small saplings can be removed by hand pulling when the soil is moist. Larger shrubs might require a Weed Wrench® or a forest mulcher. From November to January, after deciduous plants have dropped their leaves, cut larger privets down to a manageable size and apply a recommended foliar herbicide at a concentration higher than is needed to control most invasive plants. The cut stump method with an herbicide application to the cut, or a basal bark treatment are also effective methods and can be applied anytime except early spring.
Japanese Honeysuckle (Lonicera japonica), generally described in the July treatment section, is best treated with foliar sprays from autumn to early winter after most native plants have lost their leaves or are dormant, but before a hard freeze (24°F). For the cut stump method, sever thick vines near the ground and treat the cut ends with a recommended concentrated herbicide from early summer into winter.
Porcelain-Berry (Ampelopsis brevipedunculata) is generally described in the July treatment section and is also included in the September section. To prevent seed dispersal, manually remove by pulling or mowing from winter to midsummer before any fruits develop for that season. From fall to winter, cut stump bigger vines and apply an herbicide immediately after. If you can reach the largest stems in the tangle, you can also use a basal bark application. Apply a concentrated, recommended herbicide mixed with horticultural oil to the lowest 12” of the stems; no cutting is needed. Be careful not to spray nearby desirable plants.
Tree of Heaven or Paradise Tree (Ailanthus altissima) is generally described in the February treatment section and is also included in the June treatment section. Cutting down live ailanthus promotes prolific resprouting. If trees must be felled, apply a concentrated, recommended water-soluble herbicide IMMEDIATELY to the top and sides of the cut stump. See the February treatment section for recommended treatment methods of cut stump, hack and squirt, and basal bark.
OTHER ERADICATION METHODS
Goat grazing is an option for some invasives such as autumn olive, Chinese privet, kudzu, and multiflora rose. Goats will also eat desirable plants, however, and the area will generally need to be grazed for several consecutive years to rid the invasives because the roots are not eaten and must be killed. Herbicides can be effectively used after invasive plants resprout.
Manually pulling plants from the soil works only if all roots are removed, otherwise the roots will sprout new plants. This make digging larger plants especially difficult. In low–quality, heavily invaded fields, large woody plants can be pulled with a chain or a tractor bucket. In many cases, manual pulling needs to be followed by herbicide treatments. Hand pulling works best on smaller, newer infestations and when the soil is moist. Please be aware that manually pulling invasive plants will disturb the soil/leaf litter area to some degree; the act of pulling a plant from the soil can bring buried seeds of that plant or other invasive plants to the soil surface where they may germinate.
Mowing is impractical in a forest setting. It makes sense only in limited circumstances, such as in a field where you might want to cut invasive grasses or woody invasives at a certain time of year to prevent flowering and seed set. You will need to mow or bush-hog several times during the growing season for several or even many years. Weed whackers with string trimmers can be used to cut herbaceous invasive plants to the ground. For example, using a string-trimmer in August-September is recommended for the control of stiltgrass before it sets seed. Be mindful that weed whacking may harm desirable plants along with the invasive plants.
Prescribed burns or controlled burns can be a feasible way to reduce the mass of vegetation so that herbicides can later be applied more effectively. Multiple burns are sometimes required. Prescribed burns are sometimes used for autumn olive, Japanese honeysuckle, Chinese privet, and newer infestations of kudzu. The roots of these plants are rarely killed, so grow back must be dealt with subsequently.
SOURCES
Feature Photo: Goats Grazing on Invasives, US Navy, Petty Officer 1st Class Michael Wagoner
Leadership of Blue Ridge PRISM, Inc., with particular thanks to William Hamersky
“How to Control Invasive Plants: Manual, Mechanical and Biological Methods,” Blue Ridge PRISM
“Controlling Invasive Plants Effectively and Safely with Herbicides,” Blue Ridge Prism
VA Dept. of Forestry Nonnative Invasive Plant Species Control Treatments
“Don’t Buy Nonnative Invasive Plants – Even If You Can,” The Garden Shed (December 2018)
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