There are weeds, and then there are difficult-to-control weeds. These weeds are highly invasive and due to their seed dispersal and suckering methods, make it difficult to contain and control them. However, control is necessary to prevent them from overtaking the garden, native bushlands, woodlands, pastures, and grazing areas. Here’s how to identify and control problematic weeds.
Image above: St John's Wort in flower
St John’s Wort is a serious weed across most of Australia. It is native to Europe, Asia, and North Africa and was introduced to Australia in the late 1800s as an ornamental plant. Years later it spread and naturalised; consequently, it is declared a noxious weed in most parts of the country.
This perennial weed has two distinct growth stages. In autumn and winter, it forms a flat rosette with dense leaves that give rise to spindly stems. In spring and summer, it grows into an erect shrub with one or multiple woody stems that can grow up to between 30-100 cm tall. The small narrow or broad leaves are arranged in opposite pairs along the stem and are dotted with translucent black oil glands. From mid-spring to early summer, dense clusters of bright golden yellow flowers appear at the ends of branches. The small flowers – approximately 22 mm in diameter – are followed by sticky three-chambered red-brown fruits that contain small cylindrical light brown to black seeds.
Fruits ripen in summer and split to release seeds in autumn to winter. An established plant can produce up between 15,000 to 30,000 seeds in a year and can remain viable for up to 12 years in the soil. The seeds can be dispersed via machinery, wind, water, animals, or humans. St John’s Wort can also spread by sending out ‘suckers’ – roots grow out laterally and produce buds that form new plants – allowing it to grow and multiply quickly.
The oil glands in the leaves contain the toxin hypericin, which causes photosensitisation in sheep, cattle, horses and goats. This causes the skin to become inflamed and become severely irritated when exposed to sunlight.
How to Control St John’s Wort
To control St John’s Wort, spray weeds with Yates Ultra Tough Heavy Duty Weedkiller Ready To Use Spray or Yates Zero Ultra Tough Heavy Duty Concentrate. Apply to actively growing weeds and when plants are developing flower buds. Repeat applications may be necessary if infestations are severe.
Image above: Sweet Briar in flower
Sweet briar is a beautiful, single-flowering rose that was introduced from Europe to Australia in the early-to-mid-1800s. It was planted in gardens and on farmlands as an ornamental hedge, but soon naturalised and became a major weed across pastoral land and disturbed sites. It grows into dense thicket that restricts access, competes with pasture species, and provides habitats for feral rabbits and foxes.
Sweet briar grows into a multi-stemmed deciduous rose bush with arching canes that can reach 3 m tall. When young, the canes are green and smooth and as they age, become rough brown, woody and covered with backward curving thorns. The leaves are dark green with serrated margins and have an apple-like fragrance when crushed. From late spring, loose fragrant clusters of pink to white flowers appear and are eventually followed by bright red-orange fruit or rose hips. Each hip contains small irregular-shaped yellow seeds, which can be spread by birds or other grazers. The seeds can remain viable in the soil for up to four years.
The shrub suckers are extensive, allowing it to form a dense crown that often exceeds 1 m-diameter at the base.
How to Control Sweet Briar
For small shrubs or patches, manual removal can be effective. Dig out the bulk of the root system with a spade and mattock. Regularly monitor for regrowth as suckers and new seedlings are likely to appear. If treatment is required, apply Yates Tree and Blackberry Killer as a basal bark spray or cut stump treatment.
Image above: English Broom in flower
English broom, also known as Scotch broom, is an invasive woody weed that readily establishes in pastures, native grasslands, woodlands, and disturbed sites. Native to Europe, English broom was introduced to Australia in the 1800s as an ornamental hedge. It soon naturalised and is predominately found in the areas with high rainfall but is also capable of establishing in drier conditions. It is a declared Weed of National Significance.
English broom is a medium-sized multi-branched woody perennial shrub that can grow up to 3 m tall. The green brown stems are prominently ridged and are covered with small trifoliate or three-leaved leaves, with the centre leaflet longer than the outer two. They are usually covered in woolly grey hairs, giving the plant a silvery appearance. Bright yellow pea-shaped flowers grow in dense clusters on the ends of branches and can usually be seen from late winter to late spring but can also occur at the end of summer and into autumn.
The fruit is a flattened green pod with grey-silver hairs along the edges. The pod ages to black and is filled with 6-18 seeds that are explosively ejected up to 3 m away from the mother plant, and can be further distributed by water, machinery, animals and humans. Up to 6,000 seeds can be dispersed by one plant and they readily germinate after any soil disturbance, such as fire or grazing. They can also remain viable in the soil for up to 10 years.
How to Control English Broom
Spray actively growing plants with Yates Tree & Black Berry Killer. Avoid spraying bushes carrying mature fruit. Regrowth and seedlings may require repeat sprays, particularly after any soil disturbance.
Yates Products to Control English Broom
Image above: Camphor Laurel at various growth stages -
advanced tree (left), new suckers (middle), and young tree (right)
Camphor laurel is a large attractive tree with a sprawling dense canopy. Native to Asia, it was introduced to Australia in the mid-1800s as an ornamental windbreak. It continued to be planted well into the 60s and 70s, until its weedy nature was realised.
Camphor laurel is a large evergreen tree that grows between 20-30 m tall. The stems and bark on young seedlings are bright green with a red tinge that age to grey-brown with a rough fissured texture. The leaves are glossy green with a dull underside and slightly wavy margins. When crushed, the leaves have a distinctive camphor fragrance. Clusters of small white flowers appear at the ends of branches in spring and are followed by small green berries that age to black when they ripen in autumn. Each berry contains one seed and a mature tree is capable of producing up to 100,000 seeds per year.
The seeds are dispersed by birds and other animals and germinate more readily once they have been ingested. Seeds can also remain viable in the soil for up to three years. Seedlings do not grow quickly until the root system is established. Once mature, it forms a dense canopy that smothers existing vegetation with shade and suppresses the regeneration of native seedlings.
While it is a declared noxious weed in various parts of Australia, the trees have become a food source for local fauna. As such, a gradual program for removal and replacement with an alternative habitat needs to be considered, to ensure local fauna are not displaced. Check with your local council’s weed officer for more information regarding removal in your area.
Image above: Camphor laurel leaves
(Camphor laurel images courtesy of Elise Dando)
How to Control Camphor Laurel
It’s best to control camphor laurel when trees are young. For seedlings (up to 3 m tall), spray stems and foliage thoroughly with Yates Tree & Blackberry Killer. For larger seedlings (up to 10 cm diameter), apply Yates Tree & Blackberry Killer as a basal bark spray or as a cut stump treatment.
Yates Products to Control Camphor Laurel
Image above: Castor Oil Plant in fruit
Castor oil plant is a widespread weed across Australia. Native to Africa and Asia, it was introduced in the early 1800s either as an ornamental garden plant or medicinal crop. It has now naturalised in most states and territories, particularly in wastelands and along creek beds.
The castor oil plant is a large straggly branching shrub, generally growing between 2-3 m tall. It prefers warm and subtropical climates, where it grows as a long-lived perennial weed, but in frost-prone zones, it grows as an annual. The dull pale green stems are hollow and covered with large seven-to-nine-lobed leaves. Each leaf has a prominent central vein and the margins are lightly serrated. The leaves are glossy reddish-green when young and age to glossy green and have a distinctive offensive smell when crushed.
Clusters of red (female) and yellow-green (male) flowers appear at the ends of branches from summer to autumn. Once pollinated, female flowers form a small soft red or green blunt-spiny fruit that are made up of three segments, with each segment containing a smooth black and fawn coloured patterned seed. The seeds are explosively ejected – up to 5 m – from the plant when ripe and can be further spread by machinery, animals and humans. Seeds germinate readily with soil disturbance, such as fire or grazing, but can remain viable in the soil for four to seven years.
Each seed contains the toxin, ricin, which is poisonous to animals and humans. The leaves also contain ricin, but at a lesser amount.
Image above: Castor Oil Plant fruit
(Castor Oil Plant images courtesy of Elise Dando)
How to Control Castor Oil Plant
Small plants can be hand removed, ensuring the roots are completely pulled out. For larger areas or if chemical control is required, apply Yates Tree & Black Berry Killer as a basal bark spray or as a cut stump treatment. Repeat sprays or treatments may be necessary.
Image above: Large clump of young Fennel
Native to Europe and Asia, fennel was introduced to Australia in the early 1800s for various culinary and medicinal purposes. It soon spread and naturalised and can be mostly found growing along roadsides, neglected sites and near waterways. All parts of this plant are edible, smell strongly of aniseed or liquorice and are often harvested for culinary purposes – it is a cultivated crop in Tasmania. However, as it can be quite invasive, it’s best to cultivate the non-weedy forms, like Florence fennel (Foeniculum vulgar var. dulce) and bronze fennel (Foeniculum vulgar ‘Purpureum’).
Fennel is a perennial herb that grows between 1.5-2 m tall. Its upright stems are heavily branched and covered with blue-green fine feathery fern-like foliage. Long flowering stems appear from late spring, each producing clusters of 10-30 small flowers on the ends. The yellow-green flowers are replaced by small green to brown ovoid-shaped fruit that contain two seeds. The seeds are tiny (3-6 mm long), but prolific and highly aromatic. They typically fall near the mother plant, but can be spread further by machinery, water, animals and humans.
Once established, fennel can form dense infestations that compete with existing vegetation and can completely exclude new plants. Fennel also has a deep taproot with many lateral roots that can be easily ripped up by machinery and transported into new areas, where they establish and re-shoot.
Image above: Fennel flower
(Fennel images courtesy of Elise Dando)
How to Control Fennel
To control fennel, use Yates Tree & Black Berry Killer. Spray weeds between 1-2 m tall in late spring to early autumn, when bushes are actively growing. For a convenient ready-to-use product, try Yates Ultra Tough Heavy Duty Weedkiller Ready To Use Spray. Monitor for signs of regrowth or new seedlings and re-spray as required.
Yates Products to Control Fennel
Image above: Prickly Pear (Opunita monacantha) in flower
Prickly pear collectively refers to a group of cacti from the Opuntia genus. They are native to the Americas, and Opuntia monacantha is thought to be the first species introduced to Australia in the late 1700s. It was brought over as a horticultural crop to establish a cochineal dye industry. Other opuntia species were also introduced and used as ornamental plants and hedges, but they quickly grew out of hand, taking over homesteads and escaping into nearby areas. They are a declared Weed of National Significance.
Prickly pear are upright shrubs that can grow between 0.5-7 m tall, depending on the species. They’re made up of large flat paddle-like segments which act as the leaves (cladodes). The pads are covered in areoles, from which stout spines or tufts of finely barbed bristles grow. Each areole is a potential growing point, from which flowers, roots or a new pad can form. From late spring, large yellow, white, orange, red, pink or purple flowers appear along leaf margins and are followed by spiny reddish-purple pear-shaped fruit. The pulp contains numerous hard-coated seeds that can survive the digestive tract of animals and tolerate heat and drought-like conditions.
The seeds are generally scattered nearby but can be further distributed by birds and other fruit-eating animals, flood waters, machinery and humans. Fleshy plant segments can also drop and take root.
Image above: Prickly Pear (Opunita stricta) in fruit
(Prickly Pear images courtesy of Elise Dando)
How to Control Prickly Pear
Treat prickly pear with Yates Zero Ultra Tough Heavy Duty Concentrate when plants are actively growing. Watch out for signs of regrowth and spray as required.
Yates Products to Control Prickly Pear
Image above: Dense tufts of Pampas Grass in flower
This beautiful ornamental grass is such a statement piece; it’s one of the main reasons it was introduced to Australia in the 1800s. Native to South America, this tussock forming grass was used as an ornamental garden plant and a source of fodder, but because of its ability to reproduce and spread rapidly by seed, it quickly escaped and naturalised in bushlands and roadsides. It grows into dense stands and can crowd out native vegetation, invade urban bushland and restrict access to land or grazing areas.
Pampas grass grows into a large tuft of grass, with long and narrow bluish-green leaves. The lance-like leaves can grow up to 2 m long with pointed tips, sharp finely toothed margins and a distinct mid-vein running along the centre. From late summer, large feathery flowers appear atop thick flowering stems – each growing between 2-4 m tall, occasionally reaching 6 m in height. The plumes are white, cream, or silvery and age to a light tawny brown. Each flower head is made up of to 100,000 flowers and has the potential to produce up to the same amount of seeds. The seeds or grains are elliptical and straw-coloured, and are easily dispersed by humans, animals, wind, water and machinery.
How to Control Pampas Grass
To control pampas grass, treat with Yates Zero Ultra Tough Concentrate when bushes are actively growing. Regrowth and seedlings may require repeat spray. Do not spray if carrying mature fruit.
If flower heads are present, carefully bag heads and dispose of them in the bin.
Yates Products to Control Pampas Grass
Image above: Chinese Apple in fruit
Chinese apple, also known as Chinee apple and Indian jujube, is native to Asia and Africa. It was introduced in the late 1800s, when Chinese gold miners joined the gold rush and planted the tree around the garden for edible purposes. It grows into dense thickets that can significantly limit the use of pastoral lands. It can be found in WA, NT and QLD, although it’s mostly prevalent in the dry tropics of north and central QLD.
Chinese apple grows into a densely branched large shrub or small tree, between 6-8 m tall. The zigzag shaped branches have a thorn and leaf at each angle. The leaves are rounded, glossy green with silver or rusty coloured undersides. Small greenish-white flowers appear in summer and produce an unpleasant scent. They are soon followed by small green to pale yellow rounded fruit (15-30 mm) that age to reddish-brown.
The fruit is favoured by animals and some humans, and this helps with seed dispersal. Seeds can also be further distributed by floodwaters and can remain viable in the soil for up to two-and-a-half years. Established trees are capable of producing between 8,000-10,000 seeds annually. They also sucker and vigorously reshoot if the top of the canopy is damaged or killed.
How to Control Chinese Apple
To control Chinese apple, apply Yates Tree & Blackberry Killer as a basal bark spray or as a cut stump treatment. Watch out for suckers and treat as required.
Image above: African Olive in fruit
The African olive (Olea europaea subsp. cuspidata) and European olive (Olea europaea subsp. europaea) are common and widespread weeds of Australia. Native to Africa and parts of Europe, both these trees were introduced to Australia in the 1800s, with the African olive grown as an ornamental hedge and the European olive for its edible fruit. They both soon spread and naturalised, invading bushlands and formed dense monocultures that excluded any other vegetation.
Both trees look very similar, growing into multi-branched trees between 2-10 m tall. The narrow elliptical leaves are grey-green above with a yellowish-brown (African) or silvery-grey (European) underside. The leaves have a prominent midrib and pointed tips. Small white to yellow-green tubular flowers appear at the ends of branches from spring to summer, with fruit forming shortly after. African olives are small (5-10 mm) oval, purple-black when ripe with a thin layer of flesh surrounding a hard seed in the centre, whereas European olives are slightly larger (20-40 mm), more rounded and have a thicker layer of flesh around the seed.
Seeds are easily spread by water, animals, humans, machinery and motor vehicles. Seeds typically germinate in autumn, but can also persist in the soil for up to five years. Mature trees can also send up many suckers, particularly if trees are damaged from environmental conditions, attempts to remove stumps or herbicide applications.
Image above: mature African Olive tree
(Olive images courtesy of Elise Dando)
How to Control African and European Olive Trees
You can remove young seedlings by pulling them out, ensuring all roots are removed. If treatment is required, use Yates Tree and Blackberry Killer as a basal bark spray or cut stump treatment.