5.4 Invasive Species in London

Description

Common Buckthorn, also known as European Buckthorn, is a woody plant that ranges in size from a shrub to a small tree. Buckthorn leaves are opposite to sub–opposite with veins that start at the stem and curve toward the tip of the leaf. It has black buds that lie close to the twig. A small thorn extends out from the end of most twigs. The bark is smooth and shiny when young and rough and textured when mature. Buckthorn has many clumps of black berries starting in the late summer.

Introduction

Common buckthorn was brought over from Europe around the 1880s and was planted widely around the country in hedgerows and windbreaks.

Impact

Common buckthorn is the most common tree in London and is continuing to spread. Birds and animals eat buckthorn fruit and spread the seeds in their droppings. The seeds contain laxative properties that ensure they are spread widely and rapidly. Seedlings often get established on the edge of a forest and then quickly spread into the interior, forming dense stands that can tolerate shade and suppress other vegetation. Buckthorn is usually the first shrub to leaf out in the spring and the last to drop its leaves late in the fall, making it difficult for native species to compete for sunlight. It also changes the nitrogen composition of the soil, which makes it even harder for other species to survive.

Management

A variety of chemical and mechanical methods are used to control the spread of buckthorn. You can help by volunteering at removal events around London, where small plants are pulled and larger ones removed using a weed wrench tool.

Adapted from Common Buckthorn by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Garlic mustard resembles several native Ontario plants. The easiest way to distinguish garlic mustard from other plant families is to crush the leaves. If they emit a strong garlic smell, then the plant is most likely garlic mustard.

First-year plants produce a rosette of dark green, kidney-shaped leaves. Second-year plants have triangular, alternate, sharply toothed leaves and produce white flowers with four small petals in May.

Introduction

Garlic mustard is an invasive plant native to Europe that was brought to North America in the early 1800s for use as an edible herb.

Impact

Garlic mustard is one of Ontario’s most aggressive forest invaders. It can enter a new area and become the dominant plant in the forest understory within 5-7 years, even in mature forests.

Garlic mustard displaces native spring ephemeral wildflowers through direct competition and by releasing allelopathic chemicals that change the soil chemistry and prevent other species from growing nearby. These chemicals also inhibit the growth of native trees by affecting their mycorrhizal fungi network (beneficial fungi in the soil that help trees and plants absorb nutrients and water into their roots).

Management

Garlic mustard populations are managed through various mechanical and chemical control methods. You can help by pulling garlic mustard by hand. This will need to be repeated more than once and is more likely to be successful when followed by replanting with native species. Keep an eye open for garlic mustard pull events in London, where you can learn more and lend a helping hand.

Garlic mustard is edible. Try it in the early spring in your salads, or make a garlic mustard pesto!

Adapted from Garlic Mustard by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Japanese knotweed can grow in a wide range of habitats, including along rivers, wetlands, roadsides and ditches. It has hollow, smooth, purple to green-coloured stems up to 2.5 cm in diameter that grow in bamboo-like clumps. The plant can grow 1m in height in just three weeks and maxes out at 3m. It has a horizontal root system that can grow very quickly and spread up to 10m away from the parent plant.

Introduction

Japanese knotweed is native to eastern Asia and was introduced to Canada as a horticultural plant in the early 1900s. In Ontario, Japanese knotweed distribution is not well-documented, but most observations have been in the 2000s.

Impact

Japanese knotweed forms dense thickets of vegetation that aggressively outcompete native plants. It also appears to have allelopathic properties, although further research is needed. This plant can also significantly damage infrastructure as it is able to grow through concrete/asphalt up to 8 cm thick and even through building foundations. In Ontario, Japanese knotweed is currently confined to southern parts because it is intolerant of persistent freezing conditions. Unfortunately, it is likely to spread further north as the climate warms.

Management

Both root and stem fragments can regenerate, making knotweeds very easy to spread and very difficult to kill. Mechanical control on its own is not an effective management tool due to the likelihood of missing fragments, which will quickly re-establish the population. Chemical control is the recommended treatment strategy for knotweeds, but they typically require treatment with herbicide for 3-5 years.

Adapted from Japanese Knotweed by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Phragmites is a robust, erect perennial grass growing to 5m in height. Although it grows mostly in wetlands, it can also be found growing in roadside ditches and on beaches. The invasive form of phragmites looks very similar to a native species (Phragmites americanus), making identification difficult. Invasive phragmites have tan or beige stems, with blue-green leaves and large, dense seedheads. In contrast, native phragmites have reddish-brown stems, yellow-green leaves, and smaller, sparser seedheads. Additionally, invasive phragmites grow in very dense stands with up to 200 stems per square metre, which crowds out other species. In comparison, native phragmites does not grow as tall or dense and allows for biodiversity within a stand.

Introduction

Invasive phragmites have been damaging ecosystems in Ontario for decades. It is not clear how it was transported to North America from its native home in Eurasia.

Impact

Invasive phragmites is an aggressive plant that decreases biodiversity. It spreads quickly and out-competes native species for water and nutrients. Biochemicals are also released from its roots into the soil to hinder the growth of surrounding plants. Invasive phragmites spread also reduces available natural habitat and food supply for many wildlife species. Stalks are dense and rigid, preventing wildlife from easily navigating through or nesting in a stand.

Management

Invasive phragmites is primarily controlled by applying herbicides to kill the plant. After treatment, standing dead stalks are often cut, rolled and/or burned to allow native plants to re-establish.

Adapted from Invasive Phragmites by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Red-eared sliders are medium-sized freshwater turtles with distinctive red patches on either side of their head. Both their carapace (shell) and skin are olive to brown in colour, with yellow or green stripes running down their neck, legs, and tail. These turtles spend most of their time basking in the sun on logs or rocks protruding from the water.

Introduction

The primary mode of introduction for red-eared sliders is through pet release. This turtle species is a popular pet around the world and has introduced populations on every continent except Antarctica.

Impact

Red-eared sliders compete with native turtles for food and habitat. Since these turtles are larger than most of our native species, they also outcompete the other turtles for basking space on logs and rocks. Turtles need this access to warm sunshine to maintain healthy digestion and metabolism. Most native turtle species in London are already facing threats from habitat loss, road mortality and pollution. Many native turtle species are listed as Special Concern under the federal Species at Risk Act, so the additional threat of non-native competitors is of vital concern.

Management

Putting a stop to pet release is the most effective way to protect native species and habitats from invasive red-eared sliders.

Adapted from Red-eared slider by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

The zebra mussel is a small freshwater mussel named for the striped pattern of its shell. It is typically found attached to objects, surfaces, or other mussels.

Introduction

Originally from Asia, zebra mussels arrived in the Great Lakes via ballast water from transoceanic ships in 1986 and have since spread throughout North America. They were first discovered in Fanshawe Reservoir in 2002.

Impact

Zebra mussels filter plankton out of the water, which depletes it as a food source for native species. This filtering also increases the amount of sunlight able to penetrate the water, leading to toxic algal blooms, which decreased water quality and harms other wildlife. These small mussels can also grow in dense colonies on the shells of native species, suffocating populations of already threatened populations of freshwater mussels.

Management

Controlling zebra mussel populations requires a multi-faceted approach combining immediate removal and long-term strategies to prevent new infestations. Current infestations can be removed manually but is very time-consuming. Chemicals can also be used to treat localized infestations but must be used cautiously to avoid harming non-target species.

Preventative measures are the most effective way to control zebra mussels. Public education on cleaning boats and equipment is crucial to prevent transferring mussels from contaminated sources to other waterways around Ontario.

Adapted from Zebra and Quagga Mussels by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Goldfish are common pets that are known for their bright orange colour. This orange colour is the result of selective breeding over thousands of years. Goldfish vary in size depending on their habitat. Goldfish kept in smaller indoor aquariums only tend to grow about 2.5-5 cm long but can grow much larger in wild ecosystems.

Introduction

Goldfish are one of the most available fish species in the aquaculture industry because they are a low-maintenance pet. As a result, the primary pathway of spread is intentional release once their owners are no longer willing to care for them.

Impact

Goldfish are extremely damaging to local aquatic ecosystems. When released into the wild, goldfish can grow to be about the size of a football and may live up to 30-40 years old. These fish reduce the populations of native fish species by preying on them and outcompeting them for food.

Management

Reducing the spread of goldfish is as simple as not letting them loose in the wild. You also should not flush the fish down the toilet, alive or dead, because it can pass disease to other fish species. Before purchasing a goldfish, consider what you will do with it once you no longer wish to care for it.

Adapted from Goldfish by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

House sparrows are small, plump songbirds that grow to be 15-17cm long. Males have vibrant and distinct colouration, whereas females appear more monotone and streaky brown (Read more in the A Closer Look box on sexual dimorphism below).

Introduction

Birds from England were intentionally released into New York City in the mid-1800s as a control method to decrease linden moth populations.

Impact

House sparrows are territorial and aggressive. They disrupt native songbird biodiversity by preventing native species from nesting/reproducing successfully. House sparrows get the ideal nesting sites over native species because they build their nests in March before many native birds return from migration. House sparrows will also compete with native birds for staple food resources, especially at bird feeders, where they will overcrowd and chase other approaching species away.

Management

There are many approaches to managing house sparrows, including preventing nesting, controlling food availability and even destroying nests. You can help control house sparrow populations by blocking the entrances to your backyard birdhouses until native species return (early to mid-April). This gives native species a chance to claim these nesting locations.

Adapted from House Sparrows by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

European starlings are stocky black birds about the size of robins. They have glossy black plumage with a metallic/iridescent sheen and long, pointed bills.

Introduction

In 1890, approximately 100 starlings were released in Central Park, New York, by a group led by Eugene Schieffelin. This group aimed to introduce all bird species mentioned in the works of William Shakespeare to North America. The starlings quickly adapted to their new environment and spread across the continent. There are now over 200 million starlings in North America alone.

Impact

European Starlings have become one of Ontario’s most numerous birds. They are aggressive birds that outcompete native bird species for nesting sites and food. The Global Invasive Species Database includes starlings in its “100 of the World’s Worst Invasive Alien Species” list.

Management

Controlling starling populations is a challenging task due to their adaptability and prolific breeding. Homeowners can install bird spikes or other physical barriers on ledges, roofs, and other structures to prevent starlings from perching and roosting in particular areas, but there are no large-scale measures to control the population of starlings.

Adapted from European Starlings by the Cornell Lab of Ornithology, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Emerald Ash Borers (EABs) are highly destructive invasive beetles that primarily target ash trees (Fraxinus species). They are bright metallic green and are around 8-14mm long.

Introduction

Native to Asia, EABs were likely introduced to Detroit in the 1990s, hidden inside wooden shipping crates. The EAB spread to Ontario in 2002, killing up to 99% of ash trees in its path.

Impact

The EAB has killed millions of ash trees in Ontario, Quebec, and many U.S. states. The adult beetle lays eggs on ash trees, which then hatch into larvae. The larvae feed on the inner bark, which disrupts the tree’s nutrient and water transport systems, eventually girdling the tree and leading to mortality. To this day, it continues to devastate the ash tree population as it spreads in all directions across North America, where ash trees are present.

Management

There are regulations in place to reduce human-mediated spread of the EAB. Regulations for wood packaging materials used in international trade require wood to be treated to kill any possible pests to prevent their spread. Additionally, regulations restrict the movement of firewood to slow the spread of invasive pests, including EAB. You can help prevent the spread of invasive species by always following these regulations.

Adapted from Emerald Ash Borer by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Beech Leaf Disease (BLD) is a serious and emerging threat to beech trees, primarily affecting American beech (Fagus grandifolia) trees. The disease is characterized by dark green, interveinal banding on the leaves, which can be observed from early spring. As the disease progresses, leaves become leathery and curled and have a thickened texture. Eventually, the disease causes premature leaf drop, leading to a decline in the tree’s overall health.

BLD is likely caused by an invasive nematode, Litylenchus crenatae mccannii. Further research is being conducted to determine if the nematode itself produces a toxin that causes the disease or if there is another pathogen involved.

Introduction

Little is known on the origins of BLD but it is believed that the nematode may have been introduced to North American through the human transport of wood. BLD was first discovered in North America in 2012 in Ohio. It was first documented in Ontario in 2017.

Impact

Beech trees are already at risk from beech bark disease, so BLD could devastate our local beech trees. Beech trees are valuable nut-producing trees and provide food for many forest-dwelling animals.

Management

As of this time, the transmission of this disease in not currently known, so no effective control or eradication measures have been developed. Research is currently underway to determine the vector that beech trees are infected by this disease. Best management practices will be updated as research continues.

Adapted from Beech Leaf Disease by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Oak wilt is named after the characteristic leave wilting observed on infected trees. Bretziella fagacearum, a fungus, spreads through the vascular system of oaks and restricts the movement of water and nutrients up towards the leaves. The leaves of infected oaks can start to wilt and drop prematurely, eventually resulting in complete defoliation. The leaves will begin turning brown at the outer edges first and will move in towards the middle margin. Leaf discolouration and wilting typically starts at the top of the canopy and moves down over time.

Introduction

Bretziella fagacearum is believed to have been present in North America since the early 1900s. It was first detected in Ontario at a residential property in Niagara Falls in June 2023, marking the first instance of the invasive pathogen in Canada. Oak wilt has not yet been observed in London, but the public should help monitor local oak trees for signs of infection.

Impact

Oak wilt could have devastating impacts to oak populations in Canada. All species of oak trees (Quercus sp.) have been found to be susceptible to oak wilt, with species of red oak being the most seriously affected. The loss of oak trees could impact the survival of many insects and forest-dwelling animals by reducing their food supply.

Management

When a diseased red oak dies, the fungus produces sporulating mats on the dead tree. Nitidulid beetles, or bark beetles, then feed on these fungal mats and pick up spores on their bodies, which they then carry from the infected tree to wounds on healthy trees. To prevent spore mats from forming, infected or dead oaks should be removed and disposed of.

The best way for you to help is by reporting any sightings of possible infection using iNaturalist or EDDMapS. Early detection allows for early intervention.

The fungus can also be spread from humans through the transport of infected wood products. You can help reduce further spread by ensuring that you never transport firewood.

Adapted from Oak Wilt by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.

Description

Spotted lanternfly (SLF) is an eye-catching insect native to China that has become an invasive pest in the United States and has the potential to spread to London. The insect is approximately 1” long with wings that are pinkish-grey with black spots and black veins at the tips. While getting ready for flight, the forewings open, and the bright red underwings become visible.

Introduction

SLF was first detected in Pennsylvania in 2014 and has since spread throughout the Eastern United States. The SLF is an imminent threat to Ontario, including London.

Impact

The SLF is a voracious eater that feeds on over 70 species of plants and trees. It threatens to severely impact Ontario’s viticulture (wine), fruit-tree, and maple industries, which have a combined estimated worth of over $530 billion/year in Canada.

Management

Southwestern Ontario is currently monitoring for SLF. Community science can help ensure early detection to allow for a rapid response if the SLF arrives.

Because of its distinctive appearance, the SLF is not easily confused with any other insect known to occur in Canada. Community scientists should learn to recognize SLF at all life stages (eggs, nymphs and adults) and report all sightings to the Canadian Food Inspection Agency.

Community scientists can also help by uploading observations of the Tree of Heaven, SLF’s primary host, onto iNaturalist or EDDMapS. Mapping the locations of these trees can help identify areas most at risk so that these areas can be monitored more closely. The Tree of Heaven itself is an invasive species, so may even be destroyed to help reduce the chances of SLF invasion.

The United States Department of Agriculture is also turning to community scientists for help with mechanical control. They are requesting that the public search for spotted lanternfly egg masses on vehicles, trees, and other outdoor surfaces during early spring then smashing them or scraping them off, sealing them in a plastic bag and disposing of them in the trash (USDA, 2024).

Description	Photos (Hidden egg mass, young nymph, adult – closed wings)	Photos (Visible egg mass, mature nymph, adult – wings open)
The spotted lanternfly will lay their eggs on smooth plant and non-plant surfaces. The eggs will hatch in spring or early summer. Freshly laid eggs will be covered in a grey waxy coating.
The lanternfly nymph will be identifiable by the white spots on its back and legs. More mature nymphs will also have red colouration.
Adult lanternflys have uniquely coloured light brown/grey wings with spots at the front and speckled bands at the back. Their rear wings are red in colour and have black spots near the front and white and black bands at the back. Their abdomen is yellow with horizontal black stripes.

Adapted from Spotted Lanternfly by the Invasive Species Centre, used under Fair Dealing for Educational Purposes (Canada). Modifications: restructured and summarized.