Sources: EDDMapS, TreeCanada.ca, InvasiveSpeciesCentre.ca, Ontario.ca

Zebra Mussels

Photo Credit: Smithsonian Environmental Research Center, CC BY 2.0  via Wikimedia Commons

Positively Identified in Steenburg Lake: 2021

What does it look like? It has a small triangular shell with a sharply pointed umbo (hinge end). The prominent dark and light banding pattern on the shell is the most obvious characteristic. The outer covering of the shell is generally well polished, a light tan in color with broad, dark bands across the shell. These bands can be either smooth or zigzag in shape.
What’s the harm? The Zebra mussel is considered one of the ‘World’s Worst’ invaders. They have been found in central and western Europe, Great Britain, North America, Russia and Scandinavia.

Control/Management: Preventing infestations by proper ballast water management including mid-ocean exchange and disinfection should be a priority. Physical removal by high pressure washes can be effective. Freezing, heating to high temperatures and desiccation will control D. polymorpha.

Practice Clean, Drain and Dry when taking all watercraft in and out of Steenburg Lake.  This includes motorized boats, canoes and kayaks. Please share this important information with visitors and renters to avoid them bringing invasive species into the lake.

Chinese /Banded Mystery Snail

Photo credit: Severn Sound Environmental Association

Positively Identified in Steenburg Lake: 2005

The Chinese mystery snail is an invasive freshwater aquatic snail native to Southeast Asia and Eastern Russia. Once they have become established in an ecosystem, this invader effortlessly outcompetes native mollusks and filter feeders for food and habitat, and their high filtration rate displayed when feeding can lead to water quality issues comparable to that of invasive zebra and quagga mussels when their populations are large. 

What do they look like?

The shells of Chinese mystery snails are thick and rounded and can reach lengths of 6 -7 cm. Theses shells are typically olive green in colour but can range from muted shades of greenish brown to reddish brown. Their shells have distinct sutures (lines separating whorls on the shell), with 6-7 whorls, and an oblong shaped operculum which acts like a lid, deterring predators and protecting them from harsh environmental stressors. Females of this species are typically longer lived than the males, and therefore will often grow larger.

The Banded mystery snail is another invasive look-a-like species but can be differentiated by 3-4 dark brown spiral bands .

Where do they live? The most preferred habitat of the mystery snail includes lakes, rivers, and ponds, but sightings have also been reported in marshes, bays, ditches, and harbors. They favor habitats with water depths of 3 m or less, and dislike deeper rivers with strong currents.

What’s the harm?  Like invasive zebra mussels and quagga mussels, the presence of the Chinese mystery snail in freshwater aquatic ecosystems can lead to water quality issues such as algal blooms. This effect is produced by the high filtration rate of plankton the Chinese mystery snail displays when feeding. The absence of plankton and free-floating detritus in the water produces elevated water clarity, which may seem like a positive side effect, but leads to excess sunlight penetration, generating excess photosynthesis, and ultimately results in overrun algal blooms. Chinese mystery snails also have the potential to be a vector for parasites and diseases and have been reported to clog water intake pipes. Their empty large decaying shells can also wash up on shore, discouraging recreational activities, and could create hazards if stepped on.

Practice Clean, Drain and Dry when taking all watercraft in and out of Steenburg Lake.  This includes motorized boats, canoes and kayaks. Please share this important information with visitors and renters to avoid them bringing invasive species into the lake.

Eurasian Water Milfoil

Photo Credit: Invasive Species Centre

Positively Identified in Steenburg Lake: 2018

What does it look like? Eurasian watermilfoil is a submersed aquatic perennial with roots often anchored in the hydrosoil. Plant stems are reddish-brown to light green, up to 20 ft (6 m) long, and become more branched near the water’s surface. Leaves occur in whorls of four, are 1–1.5 in (2.5–3.8 cm) long, and are feather-like with 12–24 pairs of filament leaflets. Tiny pink flowers are produced on pink emergent spikes up to 6 in (15 cm) long. Fruits are 4-chambered spheres; each chamber produces one rough-textured seed.

What’s the harm? Eurasian watermilfoil displaces native plant species and decreases the abundance and diversity of aquatic insects and fish. Decaying plant material can decrease oxygen levels, which is a further detriment to fish and other organisms. Large infestations impede water flow and can cause stagnant water conditions that create habitat for mosquitoes and the parasites that cause swimmer’s itch. Large infestations also damage fishing, hunting, boating, and other recreational activities. Eurasian watermilfoil is capable of hybridizing with the native northern watermilfoil (Myriophyllum sibiricum), and some hybrid strains have proven to be even more aggressive.

Control/Management: Practice Clean, Dry, Drain when taking all boats – including canoes and kayaks – in or out of the lake. EWM spreads by fragments that root themselves so never drive your boat through a patch of EWM: if you chop up the plant it will spread. When you snag the dreaded ‘Weed Fish’ when fishing – some sort of water vegetation – DO NOT throw it back in the lake. Instead, take it to shore, dry it in the sun and burn it.  The best time to remove EWM by hand is after fish spawning (July 1st) and before fall when milfoil becomes more brittle (Oct. 1). Dry and burn for disposal.

Glossy Buckthorn

Photo credit: Eli Sagor

Positively Identified around Steenburg Lake: 2019/22/23

What does it look like? Frangula alnus is a large shrub or small tree that can grow to heights of 30 ft. (9.1 m). Its bark is gray to brown with white lenticels. The dark green leaves are shiny, alternate (sometimes opposite), and simple with prominent venation. The flowers are inconspicuous, pale greenish-yellow to yellow in color, and occur in clusters in the leaf axis. Flowering occurs from May through September. The fleshy fruit ripens from red to a dark purple or black color. You can see ripe fruit beginning about July through September.

What’s the harm? Its rapid growth and prolific seed production make this plant an aggressive invader that can form dense thickets which shade and displace native understory plants, shrubs, and tree seedlings. This plant is native to Europe

Control/management: To control glossy buckthorn, a combination of methods like mechanical removal (pulling, cutting, girdling), herbicide application (foliar spray, stump treatment), and potentially prescribed burning, can be used, with the best timing often being before or during flowering. 

Purple Loosestrife

Photo credit: Invasive Species Centre

Positively Identified around Steenburg Lake: 2021 (North Road east of the lake)

What does it look like? Purple loosestrife is an herbaceous, erect long-lived perennial typically growing numerous stems 2½–8 ft (¾–2½ m) tall from a spreading, woody root. Stems are squarish in cross-section with 4–6 sides. Leaves have smooth margins and are lance-shaped, stalk-less, and 2–5 in (5–12 cm) long. Flowers are less than 1 in (2½ cm) across with 5–7 pink to purple (sometimes crumpled-looking) petals. Flowers occur in spiked clusters from early summer to early fall. Each flower can produce well over 100 small, light-colored seeds.

What’s the harm? Large and dense populations of purple loosestrife displace native plant species, harm waterfowl nesting habitat, have negative impacts on some amphibians and algal communities, reduce water flow and quality, and degrade hunting and fishing areas

Control/management: The best time to remove purple loosestrife from your garden is in June, July and early August when it is in flower. Small areas can be dug by hand. Cutting the flower stalks before they go to seed ensures the seeds will not produce future plants.  To dispose of purple loosestrife, put the plants in plastic bags, seal them, and put the bags in the garbage. Do not compost them or discard them in natural areas. Discarded flowers may produce seeds.

Spongy Moth (formerly gypsy moth)

Photo credit: Ontario.ca

Positively Identified around Steenburg Lake: 2021

Major Hosts: The most common host is oak but will feed on most hardwoods and sometimes spruce.

What does it look like?  Caterpillars (larvae) have five pairs of blue spots on the body near the head followed by six pairs of red spots.  The egg mass is a tan coloured felt-like mass laid on tree trunks, rocks, or other surfaces.  Female moths are large with body and wings being a cream-white color with black spots and are flightless.  Males have broad wings, tiny bodies, and are mainly brown with darker markings.  The males will fly during the day.

What’s the harm?  Defoliation of many species of hardwood trees, some defoliation of conifers by later larval instars

Control/Management: Egg masses can be removed by hand and destroyed. Landowners with large wooded tracts impacted by the spongy moth can work with neighbouring landowners to apply aerial suppression treatments. 

Dog Strangling Vine (Swallowwort)

Photo: Greg Bales, MNR

Positively Identified around Steenburg Lake: 2016

Dog-strangling vine, also known as swallowwort, is an invasive perennial vine that can cause harm to native plants and ecosystems.

What it looks like: The plant has oval leaves with a pointed tip, arranged oppositely on the stem. It has small, pink-maroon flowers that appear in clusters, followed by bean-shaped seed pods that release white, feathery seeds in late summer. 

Habitat: Where does it grow? Dog-strangling vine prefers open, sunny areas but can also tolerate light shade. It is commonly found in disturbed areas, such as roadsides, railways, and abandoned pastures. 

What’s the harm?: A fast-growing, aggressive plant that can form dense thickets, crowding out other plants. It can twine around trees and other plants, potentially causing damage or creating overhead hazards. 

Control Methods: Small infestations can be controlled by hand-pulling or digging up the entire root system, but larger infestations may require herbicides. It's important to dispose of the plant properly, as it can re-sprout from root fragments and should not be composted. 

Helleborine

Photo: H. Zell, CC BY-SA 3.0 via Wikimedia Commons

Positively Identified around Steenburg Lake: 2018

The broad-leaved helleborine is a tall, dark orchid with leaves that spiral around the stem and purple-tinged, drooping flowers. It flowers from July to September and can mostly be seen in woodlands and scrub. Height: up to 75cm.

What does it look like? A tall orchid of woodland and scrub, the broad-leaved helleborine has greenish, purple-tinged flowers that look a little 'drooping'. Strongly veined, oval leaves spiral around its stem. Look for it July to September.  The broad-leaved helleborine has broad, oval leaves, with strong veins, at its base, and smaller leaves that wind their way up its stem. A single flower spike has loose clusters of 'drooping' flowers that are greenish with a purple tinge.

Invasive Potential: Helleborine is not native to North America but has become naturalized in many regions where it was introduced as an ornamental plant. It spreads through both rhizomes (underground stems) and minute seeds, making it difficult to eradicate once established.  In areas where it's considered invasive, helleborine can outcompete native plants and disrupt ecosystems. 

Control Challenges: Due to its rhizome system and seed dispersal, controlling helleborine can be challenging, often requiring a combination of methods like manual removal, herbicide application, and potentially preventative measures. 

Did you know? Some species of wasp and bee that are attracted to broad-leaved helleborines have been noted as becoming 'intoxicated' after visiting these orchids for nectar - it appears that the flowers can contain a kind of alcohol as a result of a fungus! The bees like it so much, they come back for more, ensuring the flower is pollinated.

Sources: wildlifetrusts.org/ , indefenseofplants.com

White Sweet Clover

WhiteSweetClover_BMP.pdf

Photo: Frank Mayfield CC license

Positively Identified around Steenburg Lake: 2022

What does it look like?  White Sweet Clover (Melilotus albus) is typically a biennial plant. This means it blooms in its second year and then dies. The stem of White Sweet Clover is smooth and hairless, erect, and branched, grooved or channeled. The stems are usually up to 1.5 m in height. The root crown produces somewhere between 1 to 10 stems.

The leaves of White Sweet Clover have 3 leaflets and are alternate along the stem. Each leaflet is fully toothed. They can be hairy but are usually smooth. The leaves are 1 to 7 cm long. The middle leaflet has a distinct stalk.

The flowers appear from June to October in the plant’s second year in multiple racemes (clusters which are separate from the stem). They are white, 4-5 mm in size, and the flower stalks each have between 20 and 65 flowers.

What’s the harm?  White Sweet Clover is a threat to endangered grassland and prairie habitats in Ontario. It degrades these areas by out-competing native species. It is allelopathic, meaning the roots release chemicals into the soil which can prevent the growth of native plants. Each individual plant can produce up to 350,000 seeds. Seeds can remain viable in the soil for up to 80 years. It grows in open, disturbed areas and can invade sensitive habitats. This plant is used in roadside seed mixes because it is drought-resistant and hardy (can survive road salt). The seeds of this plant can be dispersed intentionally (in seed mix or rarely, as a cover crop) or unintentionally by vehicle tires, moving water, or as a contaminant in crop seed.

White Sweet Clover flowers are attractive to bees and butterflies and in some areas, it is a popular plant for honey production. The plant contains the chemical compound coumarin, which if ingested at certain times of the year, can be poisonous to livestock and pets by preventing blood clotting.

Control/Management: Mechanical and manual control options for sweetclover include mowing or pulling. If mowed to within one inch of the ground, and mowed regularly, sweetclover may not come back or at least will not produce seed.

Source: ontarioinvasiveplants.ca