The Neem Tree Threat

21 Jan 2015

At the legislative level, it is not considered a weed.  For the land holders who have it, it is a serious production weed taking over their best country.  On their land, it outcompetes rubber vine which is a designated Weed of National Significance.

The neem tree (Azadirachta indica) originates from the seasonally dry tropical woodlands of North East India. The tree has been promoted as a commercial tree crop due to it being a source of azadirachtin, an organic insecticide that can be extracted from its seeds and leaves. The lack of financial viability of processing neem in Australia means that most plantations in Northern Australia have failed, and neem has escaped to become naturalised at numerous sites, and is rapidly expanding away from those sites. The habitats most at risk to the invasion of neem are sandy beds, and banks of rivers and creeks across the seasonally dry tropical savannah. The neem tree has also proven to adapt well to the alluvial sandy loams where its deep roots can take advantage of underlying water tables. Moreover, the robust plant has also been observed spreading to nearby granite savannah and light lance wood country in the Gulf.

Once established, a single tree can produce up to 50,000 seeds per year. The fruit is readily ingested by birds and bats which then spread the seeds, particularly amongst other trees where they perch. Neem can also produce suckers which enable the dense stands to develop and choke out other vegetation. In the Northern Territory neem has actually been declared as a Class B & C weed under their Weeds Management Act. The declaration is a result of the efforts of advocacy by the Katherine Regional Weeds Reference Group and the Northern Territory Weed Advisory Committee. The declaration means that it is illegal to buy, sell or transport neem plants or seeds. No new plantings are permitted in the Northern Territory, and offenders will be prosecuted. There is no declaration of neem in Queensland.

In 1986 25 acres of neem tree plantation was established on the Gilbert River just North of Rocky View Station and the Gulf Development Road. Maintenance of the plantation was abandoned and within 5 years the significant spread of the neem tree away from the plantation was observed by neighbours. Within 10 years the neem took over the riparian alluvial country on Rocky View Station that isn't regularly ploughed. Rob McFarlane from Rocky View stated that he mechanically cleared the majority of his river country in 1994 only to find that within 8 years the neem had heavily infested the country that wasn't regularly sprayed or ploughed. The neem is so invasive, it has outcompeted the rubber vine on the river country and has left a seemingly impenetrable thick stand only good for hosting feral pigs.

The real concern for many land managers on the Gilbert, is that the neem tree will take over scarce valuable alluvial riparian country that is well suited to high value crops. Policy makers and advocates for Natural Resource Management need to be aware of the devastating potential to high value country in the region, lobby for legislation to declare neem as a weed in Queensland, and promote research to identify cost effective methods for controlling the invasive pest.

If you have neem trees on your property and you are concerned, you are welcome to send me an email so that I can present a case to Queensland Biosecurity ( rlf@northerngulf.com.au ) to encourage their support. At the moment the most suitable technical resource for weed control is from the Northern Territory Government which can be found on the following website:

http://www.lrm.nt.gov.au/__data/assets/pdf_file/0020/353108/Weed-Note-Ne...

If you wish to access the fact sheet with details of registered chemical applications, the Regional Landcare Facilitator at Northern Gulf can readily forward them onto you ( rlf@northerngulf.com.au).

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