[ASC-media] Media release: broomrape alert

JCA Media jcamedia at starclass.com.au
Tue Nov 22 21:48:21 EST 2005

Cooperative Research Centre for Australian Weed Management

Media Release 05/46

November 23, 2005


Branched broomrape, one of the world's most serious crop pests, has made a shock appearance in southern Australia due to perfect seasonal conditions.

Previously with only a toehold in Australia, the parasitic plant that sucks the goodness out of growing crops and can lead to export restrictions has emerged at new sites in the Murray region of South Australia.

But despite the sudden outbreak, scientists consider they may have an answer in the form of a world-first system for killing seeds while they lie dormant in soil.

The huge boomspray nicknamed the "Broominator" and a natural herbicide based on pine oil represent a major advance in weed control, offering the best means of killing off the future seed bank while still in the soil, says Dr John Matthews of the Weed CRC and Adelaide University.

"The new outbreaks mean that at least we know where the pest is," says Dr Matthews.  "You could say it has shown its hand - but we have a very promising means for controlling it."

Branched broomrape (Orobanche ramosa) is regarded one of the world's worst pests of crops such as carrots, cabbages, canola, beans and lentils as well as weeds of crops and pastures. A single plant can shed up to 500,000 seeds in a season and these may lie dormant in the soil for up to 15 years. It has invaded many countries but so far has only secured a toehold in Australia.  

"Any farm where branched broomrape is found is immediately quarantined," says Dr Matthews. "None of our overseas trading partners will accept agricultural products from Australia if they are contaminated with broomrape."

Branched broomrape has a totally parasitic life cycle, he says. It produces very large numbers of small seeds, which lie dormant in the soil until they sense the chemical signals given off by the approaching roots of another plant.

 "When a broomrape seed senses an approaching root, it grows a tube which attaches to the root and sucks the nutrients out of it," says Dr Matthews. "This very successful parasitism allows the broomrape to spend most of its life hidden underground.

"It emerges from the ground as a small plant in the spring, flowers, and produces half a million seeds per plant, all within a few weeks. Then it disappears."

Dr Matthews says that a small patch of broomrape was found in Australia in 1911, but this died out and the pest was not seen again until the 1990s. Now the present infestation has been found over an area of nearly 200,000 ha in the Murray region of SA.

The quarantine protocols, although tedious for affected farmers, mean that machinery is washed down with a seed sterilant, and stock are quarantined for a period after grazing on potentially infested land."

Dr Matthews says that control of broomrape still poses a number of technical challenges and is difficult but not impossible.

"In the long term, biocontrol using specific fungi to attack the seeds may be successful," he says. "There are herbicides which are effective at preventing the plant from setting seeds, but because the parasite emerges for such a short time, and is hard to detect, this opportunity is often missed."

Methyl bromide has been successfully used to fumigate isolated outbreaks of broomrape, but this chemical is being phased out of agricultural use following the Montreal Protocol of 1987, as a threat to the ozone layer.

A herbicide derivative marketed as Interceptor®, made from extracts of natural pine oil, is being used as a soil drench to kill the seeds of broomrape in the soil. Dr Matthews believes that this will be a very effective weapon against the parasite.

"Interceptor kills the seeds and has none of the problems of methyl bromide," he says. "It is even registered as organic.

"The disadvantage is that it has to be carried into the soil deep enough to actually reach the buried seeds," he says. "This requires very large amounts of water in non-irrigated paddocks.

"We're experimenting with a 10,000 litre boomspray - known as the Broominator - with the Broomrape Eradication Program of the SA Government.   But although it has potential, there's still a very high financial cost and cost in water per hectare," he says.

Dr Matthews says that a combination of education, vigilance, and prompt attention to any identified outbreaks are the essential elements of a program to control this very serious invasive plant.

"If the broomrape eradication program is to succeed - and failure to control broomrape would have serious financial consequences - there's an urgent need for continuing funding and government support both at State and Federal level," he says, "and continuing support from farmers all over Australia for those affected".

"So far, we've held this threat at bay. But there are untold millions of branched broomrape seeds waiting their opportunity in the Australian soil. We shouldn't give them any chance of success," he says.

More information from:
Dr John Matthews, Weeds CRC and University of Adelaide, 0419 865 824
Peter Martin, Weeds CRC, 08 8303 6693, 0429 830 366

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