Control of Invasive Vegetation

THE BRUCE TRAIL CONSERVANCY

Environment Committee

THE BRUCE TRAIL CONSERVANCY

Environment Committee

Information on Control of Invasive Vegetation

Garlic Mustard (Alliaria petiolata)

Brief Introduction

Garlic mustard is a biennial, meaning it takes two years to complete its growing cycle, and then it dies. First year plants are referred to as basal rosettes, with just a few leaves appearing. In year two, the plant actually flowers. Each plant produces seeds that continue to photosynthesize during the winter months between the two stages. A single plant can produce up to five thousand seeds that germinate the following spring. The seed is its only way of reproducing. Flowers are produced in clusters at the end of the plant, typically six to seven millimetres long. Fruit is produced in late July through August as a small oblong black seed.

Recent research demonstrates that toxic chemicals produced by the roots of garlic mustard interfere with the microscopic fungi in the soil needed to stimulate the growth of native plants, giving the garlic mustard something scientists call “displacement capacity”.

Habitat

Garlic mustard invades both forest edge and forested communities, such as river floodplains, deciduous forests, roadsides, wooded edges and forest openings. It can tolerate full sun to full shade; however, it prefers habitats with a partial canopy or shade and grows well on sand, loam and clay soils.It has no known natural enemies and is difficult to eradicate once established.

Methods of Control

The method of control depends on the level of the infestation.

Small Infestations:

Cutting flowering stems at ground level can control small infestations to prevent seed production.Cutting the plants using a hand-held motorized trimmer like those used for lawn trimming, from the top down rather than side to side should be done twice a year. To be most effective, cutting should be done prior to flowering.All cut stems should be removed from the site to prevent further distribution.

Pulling is also an effective control method on small populations.It is important to ensure that you remove enough of the stem so that no buds are left behind to send up new flowers.Pulling can be done throughout the growing season. The slender tap root with a distinctive “s” curve is easily pulled by hand, but only in light moist soils and over a minimum of 5 successive years to ensure the seed bank is exhausted.

Large Infestations:

Herbicides appear to be the only method recommended for large infestations, and even herbicides have met with limited success. The herbicide glyphosate (e.g., Roundup) applied in mid-spring can be effective in helping to control larger infestations (*).In most cases re-treatments (for 2 to 5 years) may be required to deplete the seed bank in the soil. A licensed applicator must do the application.

Pulling is not recommended as a method of controlling large infestations, since it often results in stimulating the seed bank, disturbing the soil and further compounding the problem. Biological control (and the reintroduction of microbial content to locations where garlic mustard has been removed) is also not currently recommended, as this still requires extensive research.

*Note : BTC volunteers are not legally allowed to use herbicides

Dog-Strangling Vine (Cynanchum rossicum & Cynanchum nigrum)

Brief Introduction

Dog-strangling vine (DSV) is a perennial, twining soft-stemmed vine-like plant that dies to the ground each season. It is a member of the milkweed family. DSV can grow 1–2 m (3–6 feet) in height with leaves that are 5-10 cm long. The leaves are oval in shape with a pointed tip and are arranged oppositely along the stem. They are glossy in luster and appear green in the early summer and yellow in the late summer. DSV has visible flowers from late May to mid July. These flowers have five pinkish maroon colored petals that are 5-9 mm (0.2-0.4 inches) in length. Like other milkweed species, dog-strangling vine produces pods that split open lengthwise to disperse their seeds in the late summer. These pods are abundant in July and August and appear smooth and slender with a light green color. The pods are usually 4-7 cm (1.5-2.5 inches) long. The fruits of DSV often occur in pairs and are 4-6 cm (1.5-2 inches) long and 5 mm (0.2 inches) wide.

1.2 Habitat

DSV prefers disturbed areas like highways, railways, utility and transport corridors, Christmas tree plantations, nursery and perennial crop farms, limestone quarries and abandoned pastures. Once a colony is established, DSV will quickly spread into adjacent undisturbed areas, displacing the native plant species and altering the natural vegetation.DSV can invade natural upland habitats, such as woodlots, where some type of disturbance (e.g., log lands or skid trails) has taken place. This plant has a wide-ranging light and moisture tolerance.Its habitat range includes open sunny areas to moist fully shaded forest conditions, and from extreme dry and shallow sites such as an alvar to deep well-drained sites.

1.3 Methods of Control

Mowing, cutting and burning have proven ineffective as a means of control.At best, mowing will assist in reducing seed production.the plant is often not very effective because the stems easily break, leaving behind the fibrous root system that can readily re-sprout. Biological control also appears to be limited because there are few pests or diseases found in North America that have any significant impact on controlling this invasive species.

Light Infestations: Digging up the plants (including the root systems), either manually or using mechanical means, can control light infestations. However, removal of the entire plant is generally effective only if it is done in the first year of the plant’s establishment. Care must be taken to remove the entire root, as the plant will re-sprout from buds on the rootstock. By the second year, digging becomes more difficult as the plant roots are stronger and larger. Seed spread can be controlled if the plant is dug out before it goes to seed. Digging will have to be done more than once during a season, as plants will re-grow and produce more pods.

Large infestations:

The use of herbicides has met with some success, especially for larger infestations. Glyphosate (e.g., Roundup) in at least a 3% solution can be effective if the plants are sprayed while in flower, followed by a second spraying approximately one month later (*). Additional treatments may be required for two to three years in heavy populations.

*Note : BTC volunteers are not legally allowed to use herbicides

Common Buckthorn (Rhamnus cathartica)

Brief Introduction

Common buckthorn is a small tree native to Europe and Asia. It forms dense even-aged thickets that often cause an overall reduction in the establishment of shade tolerant native shrubs and herbs. It rapidly produces seeds early in the season that are highly viable and germinate quickly. It is also an alternate host of the fungus responsible for oat crown rust, which can impact the agricultural industry.

Common buckthorn can grow to 6 m (22 feet) in height with a trunk diameter of 25 cm (10 inches) and mature specimens have irregular spreading crowns. The bark is grayish brown and becomes coarse in texture as it matures. The twigs have raised patches or lenticels and are usually tipped with a spine for a terminal bud. These spines are soft while alive, but turn to sharp thorns once they have died. In the spring, clusters of 2-6 yellowish green four petal flowers begin to emerge from stems near the base of the stock. The male and female flowers are found on separate plants. Small black fruits 6mm (¼ inch) in diameter are also produced which house 3-4 seeds. The leaves are oval in shape, tipped with a point and are green in color with minute teeth along the edges. The leaves are 2.5-6 cm (1-2.5 inches) long and are arranged oppositely, or nearly so, along the stem. They can also be identified, by observing the 3-4 pairs of veins that curve upward toward the leaf tip. The leaves and fruits of common buckthorn persist late into fall helping to disguise it from other similar species. Birds and mice eat the fruit which acts as a laxative, and unknowingly distributing the seeds, often close by the parent plant to perpetuate the population.

Habitat

The preferred habitat of common buckthorn includes a wide range of soil and light conditions, giving it the ability to invade a variety of habitats. Many forest stands such as open oak woodlots are threatened by this plant, since it can thrive in lightly shaded conditions and openings in the forest canopy, created by deadfall or intentional thinning or forest management activities

Methods of Control

Manual/mechanical removal followed by burning the subsequent year can be effective, however care should be taken to avoid excessive disturbance to the soil which can stimulate buckthorn seeds stored in the soil. Prescribed burns in the year following removal, while helpful in ensuring a higher success rate, are not effective alone in eradicating this species. It is important when attempting to control Common buckthorn to remove the fruit-producing females and follow up by pulling any seedlings that regenerate.

Mowing for 2-3 consecutive years can also be an effective means of control. Mowing must be maintained for the 2-3 year period as it takes time and repetition to reduce stem numbers, overall vigor and achieve mortality.

Herbicides have also been effective, especially in the control of large infestations. In particular, painting cut stumps with a strong solution of herbicide has proven to be effective (*). A licensed applicator must do the application. Foliar applications are not recommended as the spray can greatly impact desirable native species surrounding the target plant(s).

*Note : BTC volunteers are not legally allowed to use herbicides

References

Ontario Invasive Plant Council. 2011. Date Last Accessed: June 6, 2011. Website:

Ontario Woodlot Association. 2011. Date Last Accessed: June 6, 2011. Website: http://www.ont-woodlot-assoc.org/sw_Invasive_Species.html.

Toronto and Region Conservation and Credit Valley Conservation. A Quick Reference Guide to Invasive Plant Species.