Non-native Invasive Plant Species
In North America, there are many non-native plant species that came to this continent from Europe or Asia. Some were deliberately introduced; others arrived accidentally. Of these non-native plants, only a few have the characteristics that enable them to take over large areas of the natural environment.
Invasive plants are prolific seeders. They produce thousands, tens of thousands or even hundreds of thousands of seeds per plant per summer. If the plant is a perennial, it also reproduces by a dense root system. Invasive plants grow and spread very quickly. The insects and fungi that would hold them in check in their native environments are not present in North America. In addition, invasive plants are adaptable and can usually tolerate a wide variety of growing conditions in a non-native setting. For instance, a species that requires wet soil in Europe can be found in wet or dry areas in North America.
When a plant with these characteristics invades a given area, it suppresses the native vegetation. Eventually, a monoculture of the introduced species will take over that area.
For an excellent report by the Ontario Invasive Plant Council, see here (pdf)
Controlling Phragmites australis
Encouraged by the low lake levels, the invasive reed, Phragmites australis, is on the verge of taking over many of our beaches and wetlands. It thrives on exposed soil and sand, growing so fast and thick that it rapidly displaces native plant species.
FoTTSA approached the Ministry of the Environment, Environment Canada, and the Ministry of Natural Resources and asked that Phragmites be declared a noxious weed so that it could be controlled through professional applications of Roundup Ultra, much the most effective method of control. The request was denied and we got no guidance. In addition, the Township received a letter threatening fines if it used chemicals anywhere near water.
We need to stop the spread of Phragmites. While we are waiting for the various ministries to set appropriate policy, there are a number of methods that should help constrain it.
Note that implementing the control techniques listed below will result in the accumulation of loose plant material. It is important to collect, transport and dispose of this material carefully. Seeds, rhizomes and roots must be bagged at the removal site. It is possible to burn Phragmites, but care must be taken because this plant produces a very hot fire. Plant material can be placed in kraft paper yard waste bags and taken to the compost area at the transfer station. Do not add any part of an invasive plant to a home composter. If you gather plant material in the fall, bag it and take advantage of the yard waste pick up.
For the control of Phragmites, here’s what works:
1. Pulling & Digging — effective with individual new plants or with very sparse stands
Pulling the plant out of the ground by the stalk and digging the young rhizomes (horizontal runners, either on the surface or under ground) can be effective with sparse stands or a new single plant. Care needs to be taken to ensure that as much as possible of the buried rhizomes and roots are removed. If stalks, roots, and rhizomes are left on the ground theyÕll take root and start new plants. Follow procedures outlined above for bagging and disposal.
2. Removal of Seed Heads — to prevent broad dispersal
In late August or early September, cut the seed heads or the purplish flower heads and bag them. It is best to cut them on a day with little to no wind. This prevents the widespread dispersal of Phragmites via seeds. This technique will not kill an existing stand, nor will it prevent it from spreading via rhizomes.
3. Cutting — to weaken the root system
Cut Phragmites at the base of the stalk below the first node soon after it flowers in mid to late August or sets its seeds in September. All cut stalks must be removed from the site, and care must be taken to bag and dispose of all seeds and rhizomes. Removing the stalk prevents the energy produced in the summer and stored in the plant above ground from nourishing the rhizomes and roots. Cutting must be done several years in succession before results will be seen.
4. Vinegar injection — labour intensive, but effective with a small stand and with above ground rhizomes
This technique involves injecting white household vinegar into the stalks and rhizomes of Phragmites using a 20 cc syringe and an 18 gauge needle. These needles, which are used for horses and cattle, are available in farm hardware stores and usually come in packages of 4. Note that spraying with vinegar will not kill the plant.
Mark one syringe with a permanent felt pen. Use this one for piercing a plant or a horizontal surface rhizome at the base where it emerges from the ground, being careful to stop in the middle of the rhizome or plant. Do not push the needle out the other side. The needle will become clogged with plant fibres, but the other syringes which will only be used for injecting will remain unclogged.
Fill another syringe with vinegar and insert into the hole made by the first syringe. Inject vinegar until it starts to spill out. The diameter of the stem or rhizome dictates the volume that can be injected. Plants with stalks under 4 mm in diameter are too small to be injected.
Check back in a few days. The rhizome or plant should be showing signs of dieback and should eventually die completely. If it continues to grow from the tip, repeat the above procedure in that area.
This technique is effective in killing the parts of Phragmites plants that are injected. Household vinegar is not toxic. However, needles are very dangerous and should be used only by people properly trained in their safe use and disposal.
The association that tried this method sent along the following tips:
Leather work gloves will protect the fingers from accidental jabs by the needles. Since nothing toxic is being used, these gloves are better than rubber gloves.
Vinegar can be transported to the site in a container with a secure lid and a large opening. A yogurt container carried in a pail works well. This makes it easy to fill the syringes many times.
Place the syringes in the pail after use in order to keep track of them and to avoid misplacing them in the vegetation.
5. Harrowing — to diminish the size of large stands, IF care is taken to collect and bag all plants, roots, and rhizomes immediately
This method requires advance planning and a willingness to see it through for several years. Funds will be needed for equipment (or for an operator and equipment) and also for the purchase of native species. Equipment must be chosen and volunteers found to do the essential follow-up work. Thought needs to be given to the preservation of native species presently growing on the site and about the choice of native plants to be planted in bare areas after the harrowing has been done. As Phragmites and other non-natives, such as White Sweet Clover and Coltsfoot, are opportunistic plants that thrive in disturbed areas, native species must be made to flourish and control the site if invasives are to be kept at bay (and away from the Bay) in the future.
Here is how to proceed with harrowing:
First, cut the plants to the ground and either burn them or bag them for disposal. Then have a harrow drawn across the entire patch several times. This will pull the roots and rhizomes to the surface. A variant on this is to cut the plants to the ground and then use a roto-tiller machine to chop and expose the roots and rhizomes.
All the stalks and roots and rhizomes must be bagged immediately to make certain that the plant does not re-root itself. A new plant can grow from every node of rhizomes that are left on the ground. Be careful not to allow pieces to be removed from the site by the harrowing equipment or carried along the beach by wind, waves or foot traffic, thereby spreading them to new locations.
Both harrowing and roto-tilling will probably have to be done for several summers in a row. On each occasion, care must be taken to collect all the bits, then bag and dispose of them.
Photos of Common Reed (Phragmites australis) in flower in August:
Dog Strangling Vine (DSV)
Dog Strangling Vine, a European member of the milkweed family, was likely introduced as an ornamental plant. The vines, which can grow over 2 metres in height, twine around shrubs, trees, posts and other available objects. In this way, DSV can take over large areas and suppress other vegetation along roadsides, at forest edges and in gardens.
Note that the leaves grow in opposite pairs and the stems of the leaves form a “u” where they join the stalk. The pink or purplish flowers, which appear in June, are replaced by slender green pods later in the summer. When the pods reach maturity, they burst open and the seeds are blown away by the wind – in typical milkweed fashion.
DSV is a perennial. It will appear at the same place each year, spreading from a dense system of fibrous roots. To control this plant, the first step is to pull out the vines or cut them off at the base before the pods open. The second step is to dig out as much of the root system as possible. Check back frequently and repeat these steps whenever new shoots appear. Bag the plant material at the site, and burn it or take it in kraft paper yard waste bags to the compost area of the transfer station.
Link to more information at City of Toronto Dog Strangling Vine page
Garlic Mustard (GM)
Garlic Mustard is a non-native biennial species that was brought to North America in the 1800s to be used as a food and for medicinal purposes. When crushed, the stems and leaves produce a distinct garlic odor. GM favours moist woodlands and stream beds, but the seeds are often transported to other areas by hikers, animals and vehicles. This species emits toxic chemicals into the soil. These chemicals impede the growth of other plants, including spring woodland flowers such as bloodroot, trillium and wild ginger. Eventually, an invasion of GM in the woods will interfere with the germination and growth of tree seedlings.
In the first year, kidney-shaped leaves grow low to the ground. Second year plants, from 13 to 120 centimetres in height, produce triangular and deeply notched leaves. Four-petalled white flowers appear in May. From these flowers, a single plant can produce up to 5,000 seeds which can remain dormant for up to 5 years.
Flowering second year plants should be pulled individually. Each GM plant has a slender, crooked tap root. To remove the entire root, grasp each plant at the bottom of the stem and pull gently. This procedure will need to be repeated for several years in a row. Bag the plant material at the site, and burn it or take it in kraft paper yard waste bags to the compost area of the transfer station.
White Sweet Clover (WSC)
White Sweet Clover is a non-native biennial which was introduced in the 1600s as a forage plant. In some areas, particularly in dune environments, it can become invasive and displace the native plant species.
First-year WSC plants are small and difficult to remove. Second-year plants can range in height from about 10 centimetres to over 2 metres. In the second summer of growth, the plants will flower, produce seeds and die. WSC plants can be identified by the leaves, which are grouped in threes, but it is easier to find this species once it blooms. The spiky white flowers appear throughout the summer, peaking from mid-July to mid-August. The plants must be removed before the white petals drop off and the seeds set. A large WSC plant can produce hundreds of thousands of seeds which can remain dormant for decades.
Most second-year WSC plants can be pulled out, but the roots of large plants will need to be loosened with a shovel. WSC will not continue to grow once it has been removed from the sand or soil. The plants can be left in piles and later burned or transported to the compost area of the transfer station.
Spotted Knapweed (SK)
Spotted Knapweed is a biennial or a short-lived perennial. In the 1900s, it probably arrived from Eastern Europe in a shipment of crop seeds. Because SK releases a toxin into the soil, it can be poisonous to other plants. This species favours dry, sunny locations – dunes, abandoned fields and open areas.
The first-year plant is a rosette that grows close to the ground. In the second year, wiry branched stems reach a height of 25 to 120 centimetres. Small pinkish or purplish flowers appear, and then each plant produces 1800 or more seeds. These seeds are viable for at least 5 years.
Second-year plants can be cut, pulled or dug out. To avoid disturbing the seed bed and increasing the chances of future germination, tamp down the soil after pulling or digging. Seeds will form even after the plant has been cut or removed from the ground. Therefore, SK plants should not be left lying on the ground. If pulling or cutting is not an option, remove the flowers so that seeds will not form. Bag the plant material at the site, and burn it or take it in kraft paper yard waste bags to the compost area of the transfer station. Some people are sensitive to contact with SK. Wear gloves and long sleeves when dealing with this species.
Coltsfoot was so-named because its leaf resembles a cross-section of the hoof of a colt. Because of its medicinal properties, it was brought to North America from Europe. Today, CF is still used as an ingredient in health and beauty products. This species can quickly take over wet beaches and areas of disturbed soil.
CF is a low-growing perennial plant which spreads by seeds and a system of rhizomes and roots. It has an unusual growth pattern. In the very early spring, yellow flowers emerge before the leaves appear. Each flower grows on an upright stalk, and a whitish seed cluster soon develops. After this, the groups of leaves begin to grow. The seeds are only viable for a short period of time, but the underground rhizomes can spread quickly, producing a colony of new plants.
Energy from CF leaves is stored in the rhizomes for the following year’s early spring growth. The rhizomes are quite deep, plentiful and difficult to remove completely by hand-digging. However, this is the recommended method for controlling CF. After digging out the leaves and plants, carefully turn over the sand again and sift through it for pieces of rhizomes and roots.
Hand-digging must be repeated several times during the summer and in subsequent years. The leaves and rhizomes should be bagged immediately. This plant material can be burned or taken in kraft paper yard waste bags to the compost area of the transfer station.
see Ontario government web page here for a video and more information.