History & Distribution | Biology & Habitat | Identification | Ecological Impacts | Human Health Impacts | Control

One of New York’s most striking and dangerous invasive plants, the giant hogweed (Heracleum mantegazzianum) can make a case of poison ivy seem like a mild rash.

History and Introduction

A member of the carrot and parsley family of plants (Apiaceae), giant hogweed is native to the Caucasus region of Eurasia. Because of its unique size and impressive flower head, the plant was originally introduced to Great Britain as an ornamental curiosity in the 19th century. The plant is named after the mythological god Hercules (he of robust size and strength). It was later transported to the United States and Canada as a showpiece in arboreta and Victorian gardens (one of the first North American plantings of giant hogweed was in gardens near Highland Park in the City of Rochester, New York). It was also a favorite of beekeepers because of the size of its flower heads (the amount of food for bees is substantial). A powder made from the dried seeds is also used as a spice in Iranian cooking. Unfortunately, as with so many invasive plants, giant hogweed escaped cultivation and has now become established in a number of areas in New York (see map, below), as well as in Connecticut, the District of Columbia, Illinois, Maine, Maryland, Massachusetts, Michigan, Ohio, Oregon, Pennsylvania, Washington, Wisconsin, and Ontario and Vancouver Island in Canada. Because of its public health hazard potential and, to a lesser extent, to its potential ecological impacts, giant hogweed is on the federal noxious weed list and several state lists of prohibited plant species.

Biology & Habitat

Giant hogweed (Heracleum mantegazzianum) is a member of the carrot or parsley family, Apiaceae (Umbelliferae). Except for its size, the plant can be mistaken for a number of native, noninvasive plants such as cow parsnip (Heracleum lanatum), Angelica (Angelica atropurpurea), and poison hemlock (Conium maculatum). Of these, the plant most likely to be misidentified as giant hogweed is cow parsnip. A fourth, not-so-innocuous, invasive giant-hogweed imposter found throughout North America is wild parsnip (Pastinaca sativa). Information on how to distinguish these giant hogweed wannabees from the real thing can be found later in this profile.

Giant hogweed is a perennial herb with tuberous root stalks. It survives from one growing season to another by forming perennating buds (surviving from season to season) and enduring a period of dormancy during the winter. The plant develops numerous white flowers that form a flat-topped, umbrella-shaped head up to two and a half feet across, resembling “Queen Anne’s Lace on steroids.” Flowers form from late-spring through mid-summer. Numerous (up to 100,000), half inch long, winged, flattened oval seeds form in late-summer. These seeds, originally green, turn brown as they dry and can be spread by animals, surface runoff of rain, or on the wind, establishing new colonies. Seeds can remain viable in the soil for up to 10 years. The plant’s stems die in the fall and remain standing through the winter, topped with the huge, brown dead flower heads.

Giant hogweed’s thick hollow stems are generally one to three inches in diameter but can reach four inches. Also impressive are the plant’s lobed, deeply incised compound leaves, which can reach up to five feet in width. The plant may grow to 15 to 20 feet in height.

Identification

As mentioned earlier, there are several plants in New York and the Northeast that can be mistaken for giant hogweed. Key features for distinguishing these plants from giant hogweed are explained below. Click the identification tables to enlarge.

Giant hogweed may grow to 15 to 20 feet in height. Stems are 1 to 3 inches in diameter, but may reach 4 inches. Stems are marked with dark purplish blotches and raised nodules. Leaf stalks are spotted, hollow, and covered with sturdy bristles (most prominent at the base of the stalk). Stems are also covered with hairs but not as prominently as the leaf stalks. Leaves are compound, lobed, and deeply incised; can reach up to 5 feet in width. Numerous white flowers form a flat-topped, umbrella-shaped head up to two and a half feet across. [See ID table 1]

Native Cow parsnip, while resembling giant hogweed, grows to only five to eight feet tall. The deeply ridged stems can be green or slightly purple, do not exhibit the dark purplish blotches and raised nodules of hogweed, and only reach one to two inches in diameter, contrasted with hogweed stems which can reach three to four inches in diameter. Where giant hogweed has coarse bristly hairs on its stems and stalks, cow parsnip is covered with finer hairs that give the plant a fuzzy appearance. Both sides of the leaves exhibit these hairs but they are predominantly on the underside of the leaves. In contrast to hogweed’s two- to two-and-a-half-foot flower heads, cow parsnip flower clusters are less than a foot across. The size difference carries over into leaf size with hogweed’s five foot, deeply incised leaves replaced by leaves that are less incised and only two- to two-and-a-half-foot across.

Native purple-stemmed Angelica is more easily differentiated from giant hogweed by its smooth, waxy green to purple stems (no bristles, no nodules), and its softball-sized clusters of greenish-white or white flowers, seldom reaching a foot across. As with cow parsnip, Angelica is much shorter than giant hogweed, usually no more than eight feet tall. Angelica leaves are comprised of many small leaflets and seldom reach more than two feet across.

Poison hemlock, a non-native biennial, is also shorter than giant hogweed, growing to only four to nine feet in height. While the stem has some purple blotches, it is waxy and the entire plant (stems, stalks, leaves) is smooth and hairless. The leaves are dramatically different from those of hogweed, being fernlike and a bright, almost glossy, green. All branches have small flat-topped clusters of small white flowers. Another distinguishing characteristic is poison hemlock’s unpleasant mouse-like odor. The entire plant is toxic, and the volatile alkaloids can even be toxic when inhaled. [See ID Table 2]

Wild parsnip, like giant hogweed, is of special concern because it, too, can cause phytophotodermititis, only not usually as severe as that of giant hogweed. This plant can be found extensively throughout NY’s Southern Tier, in the region east of Lake Ontario, some Central and Western New York counties, parts of the Catskills and counties east of the Hudson River. Unlike the perennial giant hogweed, wild parsnip is biennial, producing a rosette of leaves close to the ground in its first year and a single flower stalk with a flat-topped umbel with clusters of yellow flowers in its second year. The plant reproduces by means of the seeds of these flowers; it does not re-grow from its root as does giant hogweed. Wild parsnip is much smaller than giant hogweed, seldom exceeding 5 feet in height. Wild parsnip stems are yellowish-green with vertical grooves running their length. Wild parsnip has compound pinnate leaves with 5 to 15 toothed and variably lobed yellowish-green leaves.

Ecological Impacts

Colonies of giant hogweed can become quite dense owing to the plant’s prolific seed production and rapid growth rate. Such dense stands crowd out slower growing plants, the thick hogweed canopy displacing native plants that need direct sunlight to grow. The decreased abundance of beneficial native plants can reduce the utility of the area for wildlife habitat. When riparian plants are displaced, stream bank erosion can increase and streambeds can become covered with silt.

Human Health Impacts

Giant hogweed is one of a very few North American invasive plants that can cause human health impacts as well as ecological damage, causing a significant reaction when humans come in direct contact with the plant. Spread of this plant in urban and suburban areas is viewed as an incipient public health hazard. [Wild parsnip can result in almost as severe reactions.]

Soon after humans bruise the leaves or stems of the more common poison ivy, poison oak, and poison sumac, an allergic reaction to the plants’ poisonous oil (akin to carbolic acid) causes significant skin irritation, itching, rashes and open sores. In the case of giant hogweed, however, simply simply brushing against the plant’s leaves or stems does not cause the skin inflammation. For giant hogweed to affect a person, sap from a broken stem or crushed leaf, root, flower or seed must come into contact with moist skin (perspiration will suffice) with the skin then being exposed to sunlight. Irritation is not immediate, but will usually appear within one to three days after exposure. This form of skin irritation (dermatitis) is called “phytophotodermatitis”. The plant’s clear, watery sap contains a glucoside called furanocoumarin that is a psoralen. Psoralens sensitize the skin to ultraviolet radiation and can result in severe burns, blistering, painful sores, and purplish or blackened scars. These phototoxic effects are the result of the binding of the psoralens to nuclear DNA under the influence of ultraviolet irradiation, and the subsequent death of affected cells.

The first signs of giant hogweed-caused photodermatitis are when the skin turns red and starts itching. Within 24 hours, burn-like lesions form, followed by large, fluid filled blisters within 48 hours. The initial irritation usually will subside within a few days, but affected areas may remain hypersensitive to ultraviolet light for many years and re-eruptions of lesions and blisters may occur. On rare occasions, particularly in very sensitive individuals, the burns and blisters may be bad enough to require hospitalization. A side effect of exposure to the psoralens is the production of excessive amounts of melanin in the skin, resulting in residual brown blotches called hyper-pigmentation; scars and brown to black blotches may last for several years. The worst risk of exposure to giant hogweed is to one’s eyes – getting even minute amounts of the sap in the eyes can result in temporary or even permanent blindness. Medical help should be sought immediately; by the time symptoms of burning and hypersensitivity to sunlight are apparent, the damage could already be irreversible.

The only known antidote to contact with the sap is to immediately wash skin thoroughly with soap and water, removing the sap and hopefully preventing any reaction with subsequent exposure to sunlight. Once the irritation begins, medical advice should be sought. Treatment with prescription topical steroids early on may reduce the severity of a person’s reaction. It will also be important to cover the burns and blisters with light sterile dressings to prevent infection. Long-term, use of sunblock in subsequent years may be required to prevent sensitization by sunlight again.

People most at risk include landscape technicians and yard maintenance laborers who may come in contact with the sap when cutting the plant down or using line trimmers to control new growth. Children breaking off the long, bamboo-like stems to use as play swords are also at great risk. However, sometimes direct contact with the plant is not necessary for a reaction. Farmers have been known to develop symptoms when they touch cows who have gotten the sap on their skin while grazing (cows, themselves, seem impervious to the sap). The best prevention measure is to wear long sleeves and long-legged pants when contact with the plant is a possibility.

 

Control

If it weren’t for giant hogweed’s public health impacts, the plant most likely would not be worth the effort of controlling it. Although it does have ecologic impacts, they are not as severe as many other wetland invasive plants. However, the health impacts can be severe and the plant has found itself on the federal noxious weed list and several state lists, as well. It is a particular target of parks and transportation/highway departments’ invasive plant eradication efforts. Such eradication programs can incorporate a combination of physical removal and chemical control. If undertaken properly, such programs can be done without harm to humans or damage to the environment. Recently some landowners have been known to refuse permission to allow highway departments to chemically treat giant hogweed thickets. It is believed that this is usually a case of lack of knowledge on the landowner’s part.

Giant hogweed is very difficult to eradicate. Although the stems, stalks, leaves and flowers can be killed with a number of common selective herbicides, such as 2,4-D (the third most-often used herbicide in North America), dicamba (a benzoic acid herbicide), TBA (terbuthylazine) and MCPA, these herbicides are not effective at killing the plant’s tuberous perennial roots. Another common, selective broadleaf herbicide, triclopyr (a common brand name is Brush-B-Gone®), is also effective, particularly when applied directly to the entire surface of leaves and stems during periods of active growth; numerous applications may be needed to kill the root stalk. Early application (during the bud stage and the period of active plant growth) of glyphosate (commonly sold under the trade names Rodeo® and Roundup®) is most effective. Care should be taken when using any herbicides to control giant hogweed; particular care should be taken when using glyphosate as it is nonselective and will kill both the hogweed and desirable plants such as grass. Before using any herbicide, check with your state environmental regulatory agency to find out which products are licensed for homeowner use in your state.

For those hesitant to utilize herbicides, giant hogweed can be managed using various “cultural” methods. Unfortunately, owing to the plant’s persistence and spread by blowing seeds, such control can take many seasons worth of effort to achieve 100% control. Individual plants can be dug out, removing the entire rootstalk, a difficult process, particularly in patches where the plant has spread by root growth. Mowing, cutting and use of line trimmers can be used to remove a standing crop and starve the rootstalk. Unfortunately, unless performed numerous times during a season, mowing only serves to stimulate budding on the rootstalk. All of these methods should be done with extreme care and only while wearing protective clothing and eye protection. Skin contact with soiled clothing should also be avoided. Biocontrol by grazing cows and pigs (which are apparently not affected by the plant’s sap) may also help to manage but not eliminate the plant. Care should be taken not to get sap on uncovered skin when touching livestock after the animals contact crushed or bruised hogweed.

Control of wild parsnip is less difficult than controlling giant hogweed because as a biennial, wild parsnip reproduces only from seed, not from its rootstock. This plant can be controlled by cutting the stem from the root below ground level with a shovel, spade or machete before the seed head matures.

If you find giant hogweed in New York State, you are encouraged to call New York State’s Department of Environmental Conservation (DEC) Giant Hogweed Hotline:

845-256-3111

 

Reports

2014 Giant Hogweed Annual Report

The DEC Forest Health giant hogweed crews and partner agencies (Oswego SWCD and four PRISMs (Partnerships for Regional Invasive Species Management) — APIPP, CRISP, Lower Hudson, and SLELO) had an extremely productive field season which resulted in the following achievements:

• 1,495 (93%) of the 1,613 active sites located throughout 47 counties in NY State were visited
• 501 sites previously infested (28% of all sites), no longer had any giant hogweed plants
  • 239 of these sites have been monitored for 3 years with no plants found and we now consider them eradicated
• 516 sites had only 1-19 plants (34% of active sites). The sites are getting smaller in size
• 556 sites were treated with root-cutting- 22,255 plants controlled
• 551 sites were treated with herbicide- 397,000 plants sprayed
• 316 sites were treated with flower/seed head removal- 7,677 flower/seed heads removed
• The hotline, based out of the New Paltz DEC office, received 2,491 calls and emails

2017 Giant Hogweed Annual Report

View the 2017 Report

• 2,253 confirmed sites in 49 counties (no sites discovered in any new counties)
• 1,755 of the confirmed sites are in the monitor or treatment stage
• 123 sites newly designated as eradicated for a total of 498 eradicated sites (no plants for 3 consecutive years)
• 1,804 sites (80%) have 0-99 plants
• 140 new sites identified
• 1,872 sites visited
• 1,233 sites controlled – approximately 668,000 plants controlled
• 1,106 phone calls and e-mails responded to by GH Information Line staff
• 205,857 visits to DEC’s GH webpages

 

Printable Giant Hogweed Factsheet

Printable Giant Hogweed Identification Table

Problem  |  History  |  Biology  |  Habitat  |  Management  |  New York Distribution Map

Problem

Mile-a-minute weed (Persicaria perfoliata) is a vigorous, barbed vine that smothers other herbaceous plants, shrubs and even trees by growing over them. Growing up to six inches per day, mile-a-minute weed forms dense mats that cover other plants and then stresses and weakens them through smothering and physically damaging them. Sunlight is blocked, thus decreasing the covered plant’s ability to photosynthesize; and the weight and pressure of the mile-a-minute weed can cause poor growth of branches and foliage. The smothering can eventually kill overtopped plants.

History

Mile-a-minute weed (Persicaria perfoliata (L.) H. Gross, formerly Polygonum perfoliatum) is a member of the polygonum or buckwheat family. It is native to India and Eastern Asia and was accidentally introduced via contaminated holly seed into York County, Pennsylvania in 1930. Mile-a-minute weed has been found in all the Mid-Atlantic states, southern New England, North Carolina, Ohio, and Oregon (2011). In New York, mile-a-minute weed has been recorded mostly in counties south of the northern Connecticut border. Mile-a-minute weed has a large potential to expand in cooler areas, as the seed requires an eight-week cold period in order to flower. It is estimated that mile-a-minute weed is in only 20% of its potential U.S. range.

Infestations of mile-a-minute weed decrease native vegetation and habitat in natural areas impacting plants and the wildlife that depend on those plants as well. Mile-a-minute weed can also be a major pest in Christmas tree plantations, reforestation areas and young forest stands, and landscape nurseries. Areas that are regularly disturbed, such as powerline and utility right-of-ways where openings are created through regular herbicide use are prime locations for mile-a-minute weed establishment. Small populations of rare plants could be completely destroyed. Thickets of these barbed plants can also be a deterrent to recreation.

Biology

Mile-a-minute weed is an herbaceous annual vine. Its leaves are alternate, light green, 4 to 7 cm long and 5 to 9 cm wide, and shaped like an equilateral triangle. Its green vines are narrow and delicate, becoming woody and reddish with time. The vines and the undersides of leaves are covered with recurved barbs that aid in its ability to climb. Mile-a-minute has ocreae that surround the stems at nodes. This distinctive 1 to 2 cm feature is cup-shaped and leafy. Flower buds, and thus flowers and fruit, grow from these ocreae. When the small, white, inconspicuous flowers are pollinated they form spikes of blue, berry-like fruits, each containing a single glossy, black seed called an achene. Vines can grow up to six inches per day.

Mile-a-minute weed is primarily a self-fertile plant and does not need any pollinators to produce viable seeds. Its ability to flower and produce seeds over a long period of time (June through October) make mile-a-minute weed a prolific seeder. Seeds can be viable in the soil for up to six years and can germinate at staggered intervals. Vines are killed by frost and the seeds overwinter in the soil. Mile-a-minute seeds require an eight-week vernalization period at temperatures below 10 degrees Celsius in order to flower, and therefore be a threat. Germination is generally early April through early July.

Seeds are carried long distances by birds, which are presumed to be the main cause of long distance spread. Deer, chipmunks, squirrels and even one particular species of ant is known to eat mile-a-minute weed fruit. Viable seeds have been found in deer scat; an indication that other animals may also be vectors.

Mile-a-minute weed seeds can float for seven to nine days, which allows for long distance movement in water. This movement can be amplified during storms when vines hanging over waterways drop their fruit into fast moving waters, which then spread the seeds throughout a watershed.

Habitat

Mile-a-minute weed is generally found colonizing natural and man-made disturbed and open areas and along the edges of woods, streams, wetlands, uncultivated fields, and roads. It can also be found in areas with extremely wet environments with poor soil structure, and while it will grow in drier soils, mile-a-minute prefers high moisture soils. It will tolerate some shade for part of the day, but prefers full sun. Using its specially-adapted recurved barbs, mile-a-minute weed can reach sunlight by climbing over plants, helping it outcompete other vegetation.

Management

Mile-a-minute has a number of management options that can be employed. Different sites will dictate different levels of management depending on conditions and the level of infestation. Once all the plants have been removed, on-going monitoring and management must occur for up to six years in order to exhaust any seeds remaining in the soil.

Biological Control

The mile-a-minute weevil, Rhinocominus latipes Korotyaev, is a 2 mm long, black weevil which is often covered by an exuded orange film produced from the mile-a-minute plants it feeds on. This small weevil is host-specific to mile-a-minute weed and has been successfully released and recovered in multiple locations in the U.S.

The adult weevils feed on the leaves of mile-a-minute weed and females lay eggs on the leaves and stems. When the eggs hatch, the larvae bore into the stem to complete their development, feeding on the stems between the nodes. The larvae then emerge and drop to the soil to pupate. There are three to four overlapping generations per year, with about a month needed per generation. Egg laying ceases in late summer or early fall, and the mile-a-minute weevil overwinters as an adult in the soil or leaf litter.

Mile-a-minute weevil feeding damage can stunt plants by causing the loss of apical dominance and can delay seed production. In the presence of competing vegetation, mile-a-minute weed can be killed by the weevil. The mile-a-minute weevil is more effective in the sun than in the shade. Over time, mile-a-minute weevils have been shown to reduce spring seedling counts. Biological control of mile-a-minute weed is currently the most promising and cost effective method.

For more information on the mile-a-minute weevil, check the University of Delaware Biological Control on Invasive Plants Research website:

https://cdn.canr.udel.edu/wp-content/uploads/sites/6/2016/03/09184336/HG-et-al.-2015.-FHTET-revision.pdf

Cultural Control

Cultural methods can be used to help prevent mile-a-minute weed introduction to a new area. Maintain a stable plant community; avoid creating disturbances, openings or gaps in existing vegetation; and maintain wide, shade-producing, vegetative buffers along streams and wooded areas to prevent establishment.

Manual and Mechanical Control

Hand-pulling of vines can be effective; ideally before the barbs harden, afterwards thicker gloves are needed. Pull and bale vines and roots as early in the season as possible. Let the piles of vines dry out completely before disposing. Later in the season, vines must be pulled with caution as the fruit could be knocked off or spread more easily. Collected plants can be incinerated or burned, left to dry and piled on site, or bagged and landfilled (least preferred). Dry piles left on site should be monitored and managed a few times each year, especially during the spring and early summer germination period to ensure any germinating seedlings are destroyed.

Low growing populations of mile-a-minute weed can have their resources exhausted through repeated mowing or cutting. This will reduce flower production and therefore reduce fruit production.

Chemical Control

Mile-a-minute weed can be controlled with commonly used herbicides in moderate doses. The challenge with herbicides is mile-a-minute’s ability to grow over the top of desirable vegetation, and spraying the foliage of only the mile-a-minute weed can be challenging. Pre-emergent herbicides (herbicides that prevent seed germination) can be used with extensive infestations, often in combination with spot treatments of post-emergent herbicides (herbicides applied to the growing plant) for seedlings that escape control. Small populations are better controlled with post-emergent herbicides. General chemical control guidelines can be found at http://www.docs.dcnr.pa.gov/cs/groups/public/documents/document/dcnr_20033415.pdf. Areas treated with herbicides need to be monitored and retreated as necessary when new seedlings emerge from the seed bank, see above. Please contact your local Cornell Cooperative Extension office http://www.cce.cornell.edu for pesticide use guidelines. For treating wetland areas or infestations near water, contact a certified pesticide applicator. Always apply pesticides according to the label directions; it’s the law.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Problem  |  History  |  Habitat  |  Biology and Description  |  Management and Control  |  Restoration  |  New York Distribution Map

Problem

Japanese stiltgrass (Microstegium vimineum), also known as Nepalese browntop and Asian stiltgrass, replaces native vegetation in a wide range of ecosystems including forested floodplains, forest edges, stream banks, fields, trails, and ditches. It thrives as a weed in lawns and gardens. Japanese stiltgrass grows well in many light conditions (from deeply shaded hemlock forests to sunny open fields), prefers damp conditions, and often can be found in disturbed areas. It expands into dense stands of grass that prevent desirable vegetation from growing.

Areas infested with Japanese stiltgrass have decreased biodiversity. In addition to the early-season plants that are typically crowded out by invasive species, late-season grasses, sedges, and herbs are also affected. Infested areas also have an increased occurrence of other invasive plants and decreased native wildlife habitat and can provide good habitat for invasive animals including the cotton rat which can further affect local wildlife.

Japanese stiltgrass is not preferred by grazers such as white-tailed deer, goats and horses, which adds to its ability to outcompete native, preferred vegetation. A 2010 study by Pisula and Meiners indicates that Japanese stiltgrass has allelopathic potential to inhibit seed germination.

History

Japanese stiltgrass is an annual grass that is native to China, India, Japan, Korea, Malaysia, and the Caucasus Mountains. Around 1919, it was found to have been introduced to North America, in Tennessee, most likely through its use as a packing material for porcelain. It is considered invasive in Europe, Africa, Australia, New Zealand, South America, Mexico, and many island nations. Japanese Stiltgrass has extended its range into several Asian countries surrounding its native range, including Turkey, Nepal, and Pakistan.

It could be found in 24 eastern states and territories, from New York to Florida, to Texas, and Puerto Rico (2011). New York State had 16 counties reporting stiltgrass invasions (also in 2011). Japanese stiltgrass is commonly found in association with other invasive plants including garlic mustard (Alliaria petiolata), Lady’s thumb (Persicaria maculosa), Japanese honeysuckle (Lonicera japonica), and Japanese barberry (Berberis thunbergii).

Habitat

Japanese stiltgrass is able to establish and thrive in a wide range of habitats, and is most often associated with acidic to neutral, moist soils that are high in nitrogen. After disturbance, Japanese stiltgrass readily takes advantage of shaded areas, but can proliferate in sunny openings as well. Causes of disturbance include scouring floods and soil disturbing activity such as the use of heavy equipment (especially logging), tilling, mowing, construction activities, and heavy animal impact, including that from white-tailed deer.

Biology and Description

Japanese stiltgrass resembles a small, delicate bamboo and has a sprawling habit. It grows up to 3.5 feet tall. The leaves are 1-3 inches long, asymmetrical with an off-center mid-rib, and are alternately arranged on the stalk. Each lance-shaped leaf has a noticeable stripe of silvery, reflective hairs down the length of the upper leaf surface. Unlike most native grass leaves which are rough in one direction when rubbed, Japanese stiltgrass leaves are smooth in both directions.

In late summer and early fall, one or two delicate flower spikes form at the top of each stem. Each spike of flowers (inflorescence) can either require pollination or be self-fertile depending on soil moisture and sunlight availability. Individual plants can produce between 100 and 1000 seeds. Once those seeds mature the plant dies. Seeds can remain in the soil bank for at least 3 years. Japanese stiltgrass seeds readily germinate after a disturbance.

Japanese stiltgrass spreads over large areas through transportation of those seeds, primarily through the movement of soil, overland water movement, water movement through ditches and streams, and on the feet of animals and humans. Japanese stiltgrass also stolons; rooting at the node joints along the stem, producing new stems. Stolon (or tillering) spread does die off each year, but increases the number of flower spikes on a plant.

Management and Control

Before enacting management practices, be sure to properly identify the grass. There are a few native look-alikes that can be found in association with Japanese stiltgrass (or on their own). Virginia cutgrass (white grass), Leersia virginica, Pennsylvania knotweed, Polygonum persicaria, and some other fine grasses have similar morphology. The unique line of silvery hairs found on the midrib of Japanese stiltgrass is a quick identifier.

Prevention

To minimize the chances of a Japanese stiltgrass infestation, limit disturbing areas and remediate disturbed soils quickly.

Manual/Mechanical Control

Hand pulling of Japanese stiltgrass can be effective for small populations, which is why early detection and rapid response is so important. It is shallow rooted and generally easy to pull. Pull in late summer, ideally before seed set. Pulled plants without seeds can be left on-site; if seeds have formed the plants should be removed. Pulling in late summer allows Japanese stiltgrass seeds in the seed bank to germinate but does not leave enough growing season for them to establish. Do not pull before July as seeds previously left in the seed bank can grow and go to seed.

Populations of Japanese stiltgrass can also be mowed while the plants are in flower but before seed set, late summer to early fall. Mowing will set the plants back, but mowing too early will result in the plants still being able to flower and go to seed.

Soil tilling of infested areas may also be effective. Proceed with the same restrictions as above. Tilling may not be appropriate for all sites.

Due to the length of time seeds are viable in the seed bank sites must be managed and monitored for multiple years. Hand pulling, mowing, and tilling all create disturbances and should be followed with site remediation practices.

Chemical Control

Systemic herbicides can be an interim control of larger Japanese stiltgrass infestations. In the long term, conditions must be altered to prevent reintroduction of Japanese stiltgrass and other invasive plants. Choosing grass specific herbicides over broad-spectrum herbicides can help prevent mortality of non-target plants.

Post-emergent and pre-emergent herbicides have been proven effective. Post-emergent herbicides are applied when the plant is in full leaf and ideally before seed set. Pre-emergent herbicides can be applied at intervals throughout the growing season to prevent germination of Japanese Stiltgrass seeds in the spring as well as when the soil is disturbed so there is potential for additional germination times. Combinations of post and pre-emergent herbicides are viewed as a good tactic, along with continual monitoring for seed germination.

There are reports of Japanese stiltgrass populations becoming resistant to herbicides over time as natural selection allows the more resistant plants to survive and reproduce.

Alternative Methods of Control

The New York State Office of Parks, Recreation, and Historic Preservation has been battling Japanese stiltgrass for many years in some of its parks and has developed some experimental control techniques. Park biologists have proven that covering stiltgrass with 4-6 inches of mulch (chips, leaf litter) will prevent stiltgrass from emerging (OPRHP Minnewaska State Park Preserve Experiment, 2010, 2011, and Connequot State Park Preserve, 2011). They found that seeding directly into the decomposing layer will reduce future Japanese stitgrass invasions. This treatment is suitable for treating trailside infestations and easily-accessible, small- and mid-sized patches.

Japanese stiltgrass is also not very cold tolerant. Experiments show that using cold temperatures, or dry ice, in late August kills Japanese stiltgrass and may prevent reinvasion for a few years (OPRHP Minnewaska SPP, 2006). Positively, natives are able to recover in the same year as treatment. This experiment has not yet been replicated on a large scale.

Restoration

Seeding with annual rye can be a temporary restoration practice and is a recommended first stage of complete restoration. Annual rye competes with Japanese stiltgrass enough to allow natives in the seed bank to propagate. Once Japanese stiltgrass has been suppressed for a number of years and natives have a chance to outcompete it, a formal native planting should occur. If applicable to the site, Virginia cutgrass (Leersia virginica ) and jewelweed (Impatiens capensis) are competitive native plants to consider during restoration.

Reviewed by:

Alyssa Reid, Invasive Species Field Supervisor, and Robert T. O’ Brien, Invasive Species Control Field Director, NYS OPRHP – Environmental Management Bureau, Minnewaska State Park Preserve.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Introduction  |  Description  |  Impact  |  Biology  |  Habitat  |  Management Options  |  New York Distribution Map

Introduction

Multiflora rose, Rosa multiflora, also known as rambler rose and baby rose, is native to eastern China, Japan, and Korea. It was introduced to the U.S. from Japan in 1866 as rootstock for grafted ornamental rose cultivars. The spread of multiflora rose increased in the 1930s, when it was introduced by the U.S. Soil Conservation Service for use in erosion control and as living fences, or natural hedges, to confine livestock. It was also discovered to provide effective habitat and cover protection for pheasant, northern bobwhite, and cottontail rabbit and food for animals such as songbirds and deer. These uses encouraged its distribution, usually via root cuttings, to landowners through State Conservation departments. Mulitflora rose has recently been planted in highway median strips to provide crash barriers and reduce headlight glare from oncoming traffic.  Its extensive, pervasive growth was soon discovered as a problem on pasture lands and fallow fields. Currently, mulitflora rose is found in 41 states and is classified as either a noxious weed, prohibited invasive species or banned, in 13 states, including Connecticut, Massachusetts, New Hampshire, New Jersey, and Pennsylvania.  It is also ranked among the top forest invasive plant species for the northeastern area by the US Forest Service.

Description

Multiflora rose, in the rose family (Rosaceae), is a vigorous perennial shrub. Canes (stems) root at the tips and may reach heights of up to 10 feet. The red-to-green twigs may have numerous recurved thorns; other thornless specimens occur infrequently in the eastern United States. Its pinnately compound leaves grow alternately with 5, 7, 9, or 11 oval, saw-toothed leaflets. The leaflets are nearly smooth on the upper surface and paler with short hairs on the underside. The base of each leaf stalk bears a pair of fringed bracts or stipules. The fringed stipules are the best characteristic to use to distinguish multiflora rose from other species. Multifora rose shrubs can grow to a height of 10-15 feet and to a width of 9-13 feet.

Clusters of showy, fragrant, white to white-pink, half-inch to one-inch diameter flowers, bloom in panicles, inflorescences with side stems, in late May or June. The flowers produce copious quantities of sweet pollen. Six to 100 hips develop in the inflorescence in summer and turn red by middle September, containing one to 21 seeds. The hypanthium, the large, fleshy cup-like structure on the underside of the flower, softens after early frosts, becoming tough, remaining on the plant in winter. Seed color is variable yellow to tan. The seeds themselves measure about 0.16 inches and are contained in sharp, thin-pointed structures called spicules. Seed germination is high; seeds can also remain viable in the soil for as long as 20 years. Roots are wide-ranging and capable of resprouting. In addition, stem tips that contact the soil surface are capable of rooting, through a process known as layering, to form new plants. Extensive thickets are formed this way.

Impact

Multiflora rose is extremely prolific and can form dense thickets, excluding native plant species. This non-native invasive rose invades open woodlands, forest edges, early succession pastures and fields. It also invades fence rows, right-of-ways, roadsides, and margins of swamps and marshes.

Biology

Each cane on a large plant may contain 40 to 50 panicles. Each panicle can contain as many as 100 hypanthia or hips (average of about 50) and each hip, an average of seven seeds (range of one to 22). Thus each large cane can potentially produce up to 17,500 seeds. Seeds remain viable for a number of years. It has been found that as many as 90% of the seeds are viable, in the absence of drought and stress. Multiflora rose is moderately winter-hardy, and is tolerant to many North American insects and diseases.

Habitat

Multiflora rose thrives in full and partial sun with well-drained soils. It cannot tolerate winter temperatures below -28 F. While it grows most vigorously in full sun, it can also grow in the shade, and will persist for many years under a tree canopy although it may not flower or fruit very heavily.

Management Options

Note: Mechanical and chemical methods are currently the most widely used methods for managing infestations of multiflora rose.

Mechanical: Seedlings can be pulled by hand. Small plants can be dug out or larger ones can be pulled using a chain or cable and a tractor, but care needs to be taken to remove all roots. Frequent, repeated cutting or mowing at the rate of three to six times per growing season, for two to four years, has been shown to be effective in achieving high mortality of mulitflora rose. In valuable, natural communities, cutting of individual plants is preferred to site mowing to minimize habitat disturbance. Some success has resulted from the use of goats in controlling multiflora rose.

Chemical: Herbicides have been used successfully in controlling mulitflora rose, but because of long-lived stores of seed in the soil, follow-up treatments are likely to be necessary. Applications of systemic herbicides, such as glyphosate or triclopyr, to freshly cut stomp or to re growth, may be the most effective method, especially if conducted late in the growing season. The same chemicals can be employed as a foliar spray. It is important to note that multiflora rose has the typical regenerative power of members of the rose family, and control programs must be monitored and followed up if necessary by repeated herbicide application or used in conjunction with other control methods such as mowing or burning. Plant growth regulators have been used to control the spread of mulitflora rose by preventing fruit set.

Biological: Rose rosette disease is a sometimes fatal viral disease that attacks multifora rose and other roses. The virus is spread naturally by a tiny mite. Plants affected by rose rosette disease develop witches’ brooms and small reddish leaves and shoots. The disease can kill plants in two years. This disease is not considered a useful biological control at this time because it may infect native roses and plums, as well as commercially important plants in the rose family such as apples, some types of berries, and ornamental roses.

Another biological control method involves the use of European rose chalcid (Megastigmus aculeatus), a wasp. During May and June the female deposits her eggs in the seed and the larvae overwinter. Pupa formation occurs in April to June and the adult wasps appear from the rose hip in early summer, thus completing the cycle. More research needs to be completed before considering this method of control.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Biology     Identification     Impacts     Prevention & Control New York Distribution Map

Background

Garlic mustard (Alliaria petiolata) is an invasive herb that has spread throughout much of the United States over the past 150 years, becoming one of the worst invaders of forests in the American Northeast and Midwest. While it is usually found in the undergrowth of disturbed woodlots and forest edges, recent findings have shown that garlic mustard has the ability to establish and spread even in pristine areas. This spread has allowed it to become the dominant plant in the undergrowth of some forests, greatly reducing the diversity of all species. Garlic mustard is one of very few non-native plants to be able to successfully invade forest understories.

Origin and Expansion

Garlic mustard is a non-native species originating from Europe and parts of Asia. It is believed that garlic mustard was introduced into North America for medicinal purposes and food. The earliest known report of it growing in the United States dates back to 1868 on Long Island, NY. It has since spread throughout the eastern United States and Canada as far west as Washington, Utah, and British Columbia.

Biology

Garlic mustard has a biennial life cycle, that is, it takes two years to fully mature and produce seeds. Seeds germinate in February to early March of the first year and grow into a short rosette by the middle of the summer. In the plant’s second year, a stalk develops, flowers form, and the plant dies by June. Siliques, four-sided seedpods, develop in May, containing small black seeds lined up in a row. On average, a garlic mustard plant will produce 22 siliques, each of which can contain as many as 28 seeds. A particularly vigorous plant may produce as many as 7,900 seeds (Nuzzo, 1993) although the average is more likely to be in the 600 seed range. The seeds generally germinate within one to two years, but may remain viable for up to five years in the seed bank. Seed dispersal is mainly by humans or wildlife carrying the seeds.

 

Characteristics and Identification

Identification of first year plants can be difficult; the task is made easier by smelling the garlic odor produced when the leaves of the plant are crushed. The basal leaves of an immature plant are dark-green and kidney shaped with round teeth (scalloped) along the edges; average size of the leaves is 6 to 10 cm in diameter. The petiole, or leaf stalk, of first year plants are 1 to 5 cm long. In its second year, the alternating stem leaves become more triangular shaped, 1 to 5 cm long, and have sharper teeth, with leaves becoming gradually smaller towards the top of the stalk. Leaf stalks of mature plants are hairy. As with the younger plants, second year plants have a garlic odor when crushed but the odor is less obvious with increasing age.

Garlic mustard flowers arrive in early April and die by June. Flowers develop on an unbranched (occasionally weakly branched) stalk and have 4 small white petals arranged symmetrically. Flowers are approximately 6 to 7 mm in diameter with 3 to 6 mm petals. Individual flowers contains six stamens, two shorter and four longer. Mature flowering plants reach 3.5 feet tall, although shorter flowering specimens may be found.

 

Impacts

Garlic mustard has the potential to form dense stands that choke out native plants in the understory by controlling light, water, and nutrient resources. Plants most affected by these dense stands are herbaceous species that occur in similar moist soil forest habitats and grow during the spring and early summer season. Although unsupported by the lack of long-term research into garlic mustard impacts, the plant has been circumstantially tied to decreased native herbaceous species richness in invaded forests. Researchers have found that garlic mustard is allelopathic (it releases chemicals that hinder the growth of other plant species) and has inhibited growth of both grasses and herbs in laboratory settings (Michigan State University, 2008). Some researchers also believe that these compounds may hinder the beneficial relationships some plant species have with soil fungi (Roberts and Anderson, 2001). Experimental trials have shown that removal of garlic mustard leads to increased diversity of other species, including annuals and tree seedlings (MSU, 2008).

Other aspects of the forest ecosystem may be altered due to the change in the vegetative community tied to garlic mustard invasion. While the impacts to wildlife are not completely understood, altering the plant diversity can cause a change in leaf litter availability, potentially impacting salamanders and mollusks (MSU, 2008). Insects, including some butterflies, may be affected through the lost diversity in plants and loss of suitable egg-laying substrate (MSU, 2008). Garlic mustard may also affect the tree composition by creating a selective barrier that some seedlings, such as the chestnut oak (Quercus prinus), may not be able to overcome (MSU, 2008). These changes in tree composition could have significant long-term effects.

Prevention, Control and Management      

There are few effective natural enemies of garlic mustard in North America. Herbivores, or animals that eat plant material, such as deer (Odocoileus virginianus) and woodchucks (Marmota monax) only remove up to 2% of the leaf area in a stand of garlic mustard (Evans et al. 2005). This level of herbivory is ineffective in controlling reproduction or survival of garlic mustard. Although 69 herbivorous insects have been found to be associated with garlic mustard in Europe, less than a dozen have been found on North American infestations of the species (Hinz and Gerber, 1998).

Manual removal of plant has been shown to prevent the spread of garlic mustard. Pulling by hand must remove at least the upper half of the root to prevent a new stalk from forming; this is most easily accomplished in the spring when the soil is soft. Hand-pulling should be performed before seeds are formed and needs to be continued for up to five years in order to deplete any established seed bank. This method works best in smaller pockets of invasion or in areas recently invaded to help prevent the development of a seed bank.

Chemical applications can also be effective for controlling garlic mustard, particularly in areas too large for removal by hand. In dense stands where other plant species are not present, a glyphosate-based herbicide such as Roundup® can be an effective method for removal. Glyphosate herbicides are non-selective, so caution must be used when non-target species are in the area. Chemical applications are most affective during the spring (March-April) when garlic mustard is one of the few plants actively growing. Fall applications may be used; however other plant species still in their growing season may be harmed. Readers are advised to check with local regulatory agencies to determine the regulations involved with chemical treatments.

The best method for controlling garlic mustard, or any other invasive plant, is to prevent its establishment. Disturbances in the forest understory that would allow for rapid invasion should be minimized. This would include limiting foot traffic, grazing, and erosion-causing activities. Monitoring the forest understory and removing any garlic mustard plants as soon as they are introduced will help to prevent the establishment and spread of this invader.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Biology & Identification | Impacts | Prevention & Control | New York Distribution Map

 

Background

Common buckthorn (Rhamnus cathartica) is a small deciduous tree or large shrub that can grow to six meters in height. It has dull green oval or egg shaped leaves and is easily identified by the small thorns at the tip of its branches. It is also known as European buckthorn, European waythorn, and Hart’s thorn. Common buckthorn is considered an invasive species throughout most of the northeastern and central United States and southeastern Canada because of the dense thickets it forms.

Origin

Common buckthorn is native to most of Europe (except Iceland and Turkey) and western Asia. It was brought to North America some time in the 1800s for use as an ornamental shrub and wind break but did not have wide spread distribution until the early 1900s. It is found in hedgerows, along roadsides and on ravine slopes.

Biology and Identification

Common buckthorn is a perennial shrub or small tree. It is found in lightly shaded areas and is tolerant of many soil types from well-drained sand to clay. Branches are tipped with a short thorn; a thorn may also be found in the fork between two branches. The leaves may be opposite or in an alternating pattern (both may be found on the same branch). The leaves are oval or egg shaped with small, serrated teeth. The leaf may be a dull green or a dark green with a lighter green on the under side. Flowers are small with four sepals (a modified leaf that encloses the petals and other parts of the flower) and four petals and they form small clusters from the axils (the space between a leaf or branch and the stem/stalk of the plant) of leaves or on short twigs along the stem. The flowers are a yellowish to green color. Each flower is unisexual with either four stamens or one pistil with a plant being either male or female (dioecious). The fruit or berries are small (5-6 mm in diameter) and are a dark purplish or black color. Each berry will contain four hard seeds. The common buckthorn flowers during late spring (May-June) while leaves are emerging. The berries ripen during August and September and can be found still attached to the plant throughout the winter.

Buckthorn seeds are easily spread by birds and other wildlife. It is fast growing and will reproduce from seeds or by stump sprouting. The seeds may remain viable in the soil for up to five years.

Common buckthorn can be distinguished from native and other non-native buckthorns by its sharp, thorn-tipped branches and from native Hawthorns (Crataegus spp.) on which the thorns grow from the sides of branches. It also has noticeable forward-curved side veins on its leaves and clusters of purplish-black berries that have 4 hard seeds.

Impacts

Common buckthorns form thick hedges with long branches that crowd out and shade out native shrub and herbaceous species, preventing regeneration of native plants. In fire prone areas the lack of herbaceous ground cover underneath the buckthorn hedge may prevent fires from spreading.

The common buckthorn is a host for the crown rust fungus (Puccinia coronata), an agricultural pest that inhibits the yield and quality of oats. It may also serve as a overwintering host for the Asian soybean aphid (Aphis glycines Matsumura), a pest known to damage soybeans and can spread a variety of horticultural viruses. Buckthorn leaves have a high concentration of nitrogen and the decomposition of leaf litter changes soil nitrogen content and can increase the pH levels in the soil. These changes create better growth conditions for the common buckthorn perpetuating their persistence.

Prevention and Control

There are several methods available for control of common buckthorn. These controls include mowing, excavation, cutting and burning. Repeated mowing and cutting has been shown to reduce the vigor of the plants. The plants may be removed by hand or with heavy equipment depending on the size of the shrubs. Care should be taken to not disturb the roots of other plants. The disturbed area, now devoid of the invasive plant, may become the home for new common buckthorn seedlings or other opportunistic invasive plants. As noted earlier, the seeds may persist in the ground for five years resulting in new growth.

Prescribed burns are another way to control buckthorns in fire-adapted ecosystems. Fires will top-kill mature plants; however sprouting can occur from the roots and trunks.

There are also several chemical methods (Table 1) available for controlling common buckthorn. These are generally applied to the stumps after cutting to prevent sprouting. There are no currently known biological controls for common buckthorn. Research into biological controls for common buckthorn is in progress.

Table 1. Herbicides effective on Common buckthorn (Rhamnus cathartica)

Chemical Name	Use
Triclopyr amine	Cut stump
Triclopyr ester	Cut stump or basal bark
Glyphosate	Cut stump

(MNDNR 2008)

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.