Leslie Massey
The neem tree (Azadirachta indica), native to the Indian subcontinent, has become a pest in Australia, where it was originally introduced for ornamental, agricultural, and commercial purposes. Neem trees are fast-growing and highly invasive, dominating and killing native trees and threatening endangered habitats. They are now established throughout Australia's northern tropics and subtropics, particularly in Queensland, the Northern Territory, and Western Australia, where they are listed as a weed.
| Characteristics | Values |
|---|---|
| Scientific name | Azadirachta indica A.Juss |
| Native to | India and Bangladesh |
| Regions of Australia where it grows | Queensland, Northern Territory, Western Australia |
| Areas where it grows in Western Australia | Kimberley region, Kununurra, Broome, Doon Doon, Kalumburu, Crossing Falls, Mud Springs, Packsaddle, Weaber Plains Road, Cave Springs |
| Areas where it grows in the Northern Territory | Katherine River system, Victoria River District, Roper and Gulf districts, Darwin, Katherine and surrounding rural areas |
| Height | 15-20 m tall (sometimes up to 40 m) |
| Crown diameter | up to 20 m |
| Annual rainfall in areas where it grows best | 450-1200 mm |
| Drought tolerance | Very high |
| Leaf description | Pinnate, compound leaves 20-40 cm long, with 20 to 30 medium to dark green toothed leaflets about 3-8 cm long and arranged in opposite pairs |
| Flower description | White flowers 5-6 mm long and 8-11 mm long grow in drooping axillary clusters from the stem; branching inflorescences can be up to 25 cm long and bear 150 to 250 flowers |
| Fruit description | Elongated, smooth olive-like stone fruit (drupe) about 1.4-2.8 cm x 1.0-1.5 cm; skin turns from green to yellow when ripe; pulp is yellowish-white, 0.3-0.5 cm thick and very fibrous |
| Seed description | Usually one brown-coated and elongated seed kernel per fruit, rarely two or three |
| Weed status | Declared pest in Western Australia; listed as a weed in the Northern Territory and by certain local governments in Queensland and Western Australia |
| Seed dispersal | By fruit-eating birds, bats, and water |
| Seed production | Up to 50,000 seeds per year by a single mature tree |
| Commercial uses | Plant spray, powder, pellets, shampoo, soap, skincare creams, capsules, tea |
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What You'll Learn
Neem trees are native to the Indian subcontinent and Southeast Asia
Neem trees (Azadirachta indica A.Juss) are native to the Indian subcontinent and Southeast Asia. They are fast-growing trees that generally reach heights of 15–20 metres (and sometimes up to 40 metres), with a crown diameter of up to 20 metres. Neem trees thrive in areas with an annual rainfall of 450–1200 mm, and are highly drought-tolerant once established. They are native to the tropical woodlands of northeast India and perhaps other parts of the Indian subcontinent, including Bangladesh.
Neem trees were deliberately introduced to Australia, where they are now established throughout the northern tropics and subtropics of Queensland, the Northern Territory, and Western Australia. They grow particularly well in sandy river beds in the dry north. In Western Australia, neem trees can be found in the Kimberley region, including Kununurra, Broome, Doon Doon, Kalumburu, Crossing Falls, Mud Springs, Packsaddle, Weaber Plains Road, and Cave Springs.
Neem trees have become a dominant species in Australia, outcompeting and killing native trees like the iconic boab and mature gums, and displacing endangered vegetation like the monsoon vine thicket. They produce up to 50,000 seeds per year, which are spread by birds and bats that ingest the fruit, contributing to their rapid spread along waterways. Neem trees also reproduce through suckers, enabling them to form dense stands.
The neem tree has a wide range of uses, including the production of azadirachtin, a broad-spectrum insecticide. Neem oil, extracted from the seeds, is commercially available and used in agriculture and gardening due to its insecticidal properties. It is effective against a wide range of leaf-eating and sap-sucking insects. However, there are conflicting reports about the safety of consuming neem products, especially for pregnant women.
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Neem trees are considered a pest in Australia
Neem trees, or Azadirachta indica A.Juss, are considered a pest in Australia. Originally native to the Indian subcontinent and Southeast Asia, the tree was introduced to Australia as a garden ornamental, for shade, and for the production of azadirachtin, a broad-spectrum insecticide. However, it has now escaped cultivation and is established in the northern tropics and subtropics of Queensland, the Northern Territory, and Western Australia.
Neem trees are fast-growing and can reach heights of 15-20 meters, with a crown diameter of up to 20 meters. They thrive in areas with annual rainfall between 450 and 1200 mm and are highly drought-tolerant once established. Neem trees have a deep taproot system and extensive lateral roots, making them highly competitive weeds. A single mature neem tree can produce up to 50,000 seeds per year, which are dispersed by fruit-eating birds and bats, contributing to their rapid spread.
In Western Australia, neem trees are declared pests, dominating and killing native tree species such as iconic boab trees and mature gums. They also displace endangered monsoon vine thickets and threaten the habitat of the Purple-crowned fairywren. Neem trees are challenging to control due to their extensive root systems. Seedlings can be removed by hand, but larger plants require the application of herbicides to the cut stumps or as a basal bark treatment. Physical removal before the fruit grows is essential to prevent seed spread.
Neem trees are also listed as weeds in the Northern Territory, where they have proliferated along creek, river, and drainage systems, including the Katherine River and Victoria River systems. Neem trees produce suckers, enabling dense stands to develop and further impacting native ecosystems. While mature neem trees in garden settings are not the focus of management efforts, removal is encouraged, and landowners are advised to remove all seedlings to prevent further spread.
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Neem trees are fast-growing and drought-tolerant
Neem trees (Azadirachta indica) are native to the Indian subcontinent (India and Bangladesh) and Southeast Asia. They were introduced to Australia as ornamental garden plants and for the production of azadirachtin, a broad-spectrum insecticide. Neem trees are fast-growing and can reach heights of 15-20 meters, with some trees growing up to 40 meters tall. They have a deep taproot system and extensive lateral roots, contributing to their competitive nature as a weed. Neem trees thrive in areas with annual rainfall between 450 and 1200 mm but are also highly drought-tolerant once established. This adaptability allows them to grow in the sandy riverbeds of northern Australia, particularly in Queensland, the Northern Territory, and Western Australia.
The fast-growing nature of neem trees is attributed to their reproductive strategy. A single mature neem tree can produce up to 50,000 seeds per year, which are then spread by birds and bats that ingest the fruit. This has led to the significant spread of neem trees along waterways and their dominance in certain ecosystems, threatening native plant species and habitats. Neem trees also produce suckers, enabling them to form dense stands and further contribute to their rapid expansion.
The adaptability and reproductive capacity of neem trees have resulted in their classification as a declared pest in Western Australia. While they were initially cultivated for commercial purposes, neem trees have now escaped from cultivation and grow wild across Australia's northern tropics and subtropics. Their rapid growth and aggressive nature have led to concerns about their impact on native flora and fauna. Neem trees have been observed to dominate and kill iconic boab trees and mature gums, displace endangered monsoon vine thickets, and threaten the habitat of the Purple-crowned fairywren.
Despite the negative ecological impact of neem trees in Australia, they possess valuable characteristics for pest control. Neem oil, derived from the seeds, leaves, or seed cake, contains azadirachtin, a potent insecticidal compound. This oil can be used to control a wide range of leaf-eating and sap-sucking insects, making it a valuable tool in agriculture and gardening. Neem preparations are sold by several companies in Australia for these purposes, showcasing the economic value of this invasive species.
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Neem trees produce azadirachtin, an insecticide
Neem trees (Azadirachta indica) are native to the Indian subcontinent and Southeast Asia. The tree was introduced to Australia as a garden ornamental, for shade, and for the production of azadirachtin, a broad-spectrum insecticide. Neem trees are now established throughout Australia's northern tropics and subtropics, particularly in Queensland, the Northern Territory, and Western Australia.
Azadirachtin is a chemical compound derived from the seeds of the neem tree, specifically from the brown-coated kernels contained within the tree's olive-like stone fruits. The compound is highly oxidized and contains a variety of oxygen-bearing functional groups, including an enol ether, acetal, hemiacetal, tetra-substituted epoxide, and carboxylic esters.
Azadirachtin is an effective insecticide against a broad spectrum of insect species, including aphids, mealybugs, caterpillars, Japanese beetles, whiteflies, mites, root aphids, and thrips. The compound acts as an insect growth regulator, disrupting the normal growth and molting processes of insects. It also interferes with reproductive functions, leading to sterility in some insects. Additionally, azadirachtin acts as an antifeedant, reducing the feeding activity of insects.
The compound can be extracted from neem seeds through a process of crushing and cold-pressing, resulting in an oil rich in azadirachtin. This oil, known as neem oil, is commercially available and can be used in agricultural and garden settings. Neem oil is also combined with other insecticides and biocontrols, such as the beneficial fungus Beauveria bassiana, to create azadirachtin-based insecticide products. These products are preferred by some due to their compatibility with a wide range of insecticides and their minimal environmental impact.
In addition to azadirachtin, neem trees produce at least 35 other ingredients with insecticidal properties. Neem oil, for example, contains other insecticidal and fungicidal compounds. When used as a pesticide, neem oil is typically mixed with water at a specific ratio to ensure effectiveness and safety. While azadirachtin and neem-based products are widely used, it is important to note that there are conflicting reports about the safety of consuming neem, and more research is needed to understand the potential risks, especially for pregnant women.
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Neem oil is used as a pesticide
Neem trees (Azadirachta indica) are native to the Indian subcontinent and Southeast Asia. It was introduced to Australia as a garden ornamental, for shade, and for the production of azadirachtin, a broad-spectrum insecticide. Neem trees have since escaped cultivation and are now established throughout Australia's northern tropics and subtropics, dominating and killing native trees and threatening the habitats of endangered species.
Neem oil, extracted from the seeds of neem trees, is a naturally occurring pesticide that has been used for hundreds of years to control pests and diseases. It is yellow to brown, has a bitter taste, and a garlic/sulphur smell. Neem oil is a mixture of components, the most active of which is azadirachtin, which is responsible for repelling and killing pests. The portion left over after azadirachtin is extracted is called clarified hydrophobic neem oil. Neem oil can be formulated into granules, dust, wettable powders, or emulsifiable concentrates.
Neem oil is an effective pesticide for a wide range of insects, including aphids, beetle larvae, caterpillars, lace bugs, leafhoppers, leafminers, mealybugs, thrips, and whiteflies. It kills insects by suffocation, covering their bodies and blocking their breathing openings. It is most effective against immature insects, as it interferes with their life cycle, including feeding, molting, mating, and egg-laying. Neem oil is also effective against soft bugs, such as aphids, when sprayed directly on them.
To use neem oil as a pesticide, it must completely cover the plant. It can be applied to the stems, leaves (including the undersides), and soil. It is important to test the product on a small area first, as neem oil can damage plants by burning their foliage, especially if they are in direct, harsh sunlight. Neem oil should be applied in the morning or evening, avoiding the middle of the day when the sun and heat could burn the sprayed foliage. It should also not be applied if rain is forecasted in the next 24 hours, as it could be washed away.
Neem oil is generally safe, and no association with an increased cancer risk has been found. However, it can be harmful, especially to children, and may cause adverse reactions in cats. It is important to always follow label instructions and take steps to minimize exposure when using neem oil or any other pesticide.
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Frequently asked questions
Yes, neem trees are prevalent in the northern tropics and subtropics of Queensland, the Northern Territory and Western Australia.
Neem trees were introduced to Australia from the Indian subcontinent and Southeast Asia.
Neem trees were brought to Australia for their shade, as a source of azadirachtin (an insecticide), and as a garden ornamental.
Yes, neem trees are considered a pest and a weed. They are dominating and killing native trees and threatening the habitats of endangered species. Neem trees also produce up to 50,000 seeds per year, which are spread by birds and bats that ingest the fruit. These seeds contain kernels that are poisonous to mammals.
Neem trees and their seeds are subject to removal and control methods. Seedlings can be removed by hand, but mature trees may require the application of herbicide.
