Cacti spread poses problem

WA's priority weed response manager Kay Bailey (left) with Agriculture and Food Minister Alannah MacTiernan.
WA's priority weed response manager Kay Bailey (left) with Agriculture and Food Minister Alannah MacTiernan.

A PRICKLY pest found throughout WA’s cropping and pastoral lands is being brought to the public’s attention this month.

November is Cactus Month and the Department of Primary Industries and Regional Development (DPIRD), other land managers like shire councils and volunteer environment and biosecurity groups are hoping to raise awareness of the risk to agriculture the Opuntioid group of cacti pose.

Activities will include community markets promotions in the South West where cacti are often sold as garden plants.

Regional Development Agriculture and Food Minister Alannah MacTiernan launched Cactus Month and a national Opuntioid cacti best practice manual in Henley Brook at the Tackling Prickly Pests forum on Wednesday, November 1.

The forum resulted from collaboration between the Federal Department of Agriculture and Water Resources and its agriculture competitiveness white paper on managing pest animals and weeds, DPIRD, the City of Swan and Shire of Mundaring.

A semi-urban location was deliberately chosen for the launch because most problem cacti infestations are started by escapees from residential gardens, remnants of historic gardens around old homestead ruins or garden waste dumped in the bush.

Many of the problem cacti can be spread by both seed dispersal via birds and segment dispersal via floods or animals brushing against them.

They thrive in challenging environments where other plants are vulnerable and they are extremely competitive and over time will reduce biodiversity and the health of endemic species, DPIRD priority weed response manager Kay Bailey told the forum.

“Not all cacti are weeds and not all cacti are invasive but there are some that are very invasive in WA, as well as Eastern States, and what we want to do is prevent any more impact,” Ms Bailey said.

“Our aim is preventing the spread and to manage the impact.

“The invasive cacti are highly disruptive, they spread very, very rapidly, they have impacts on agricultural productivity as well as environmental impacts, and impacts on recreational land use, so they are a very broad spectrum weed that everybody needs to know about.”

As an example of the impact on pastoralism, Ms Bailey cited a coral cactus problem on Tamoola station in the Goldfields that spread from three original plants over 10 years to make a total of 65 square kilometres unproductive.

Three square kilometres had to be fenced off because of the density of coral cactus plants and a flood spread segments far and wide across the station which started new cactus colonies where they came to rest, Ms Bailey said.

“In a lot of areas we are finding them (cactus) under roosting trees where the birds have spread the seeds after eating the fruit.”

Ms Bailey said they were also a problem in cropping areas and found right throughout the Wheatbelt, but in particular prickly pear, which was a significant problem in South Australia, had also become a problem near Esperance.

Ms Bailey said the impact of cactus on animal welfare was often overlooked.

Some cactus had barbed spikes which did not come out and stuck in the hide of stock and native animals causing sores and discomfort.

Animals that ate the fruit of a cactus often ended up with spikes in their mouths which made it “extremely painful” for them to forage and eat.

The cactus spikes devalued commercial hides and wool clips and were a risk for shearers in fleece, she said.

“A study some years ago (by DPIRD’s predecessor) indicated the three major pest cactus species – coral cactus is one – in the grazing area if not managed could cause an estimated $3.6 million damage a year,” Ms Bailey said.

“It’s not an insignificant impact we’re talking about.”

Cactus crowded out pasture grasses and native plants and often provided shelter for other pests like foxes and rabbits.

“There is also some thought that cactus can harbour fruit fly – the jury is still out on this one, but it is still another possibility,” Ms Bailey said.

She said 27 species of cactus were designated as weeds of national significance in 2013 and became declared weeds in WA in December 2014 under the revised Biosecurity and Agricultural Management Act.

There are 10 species in control category C1 which means their entry to WA is prohibited and if found they must be eradicated.

Wheel and chicken dance are two examples of C1 cactus sometimes found in WA.

Seventeen species in a C3 category that requires them to be managed to prevent any impact beyond the immediate area, included coral cactus, Hudson pear, prickly pear, velvet pear, Eve’s pin, bunny ears and devil’s rope cactus found in WA.

Ms MacTiernan congratulated DPIRD staff on their involvement in putting the best practice manual together to provide a helpful guide for land managers and environment volunteers.

She said it contained good descriptions of invasive cactus and a range of control methods, as well as “some case studies of experience that can be very useful for people dealing with this to see how others have had some success”.

“We know that dealing with these in the agriculture region is a very costly business and they estimate that across Australia it’s about $4 billion the (cost) impact on our agricultural output each year,” she said.

“I must say though that I’ve been out in this area (Swan Valley) with some elderly Italians who very fatherly showed me their beautiful prickly pear plantations that they absolutely love.

“We do know that we brought prickly pear into Australia as an agricultural venture, we also thought we could start a cochineal industry out of it but then it proved to be one of those things that wasn’t such a good idea.”

Ms MacTiernan said a cactoblastis moth biological control had helped manage some cacti infestation in Queensland but it was less successful in WA because of different soil types and drier climate.

“I would like to think that we could perhaps do a bit of work on that bug and perhaps engineer one that was suitable for our location,” Ms MacTiernan said.

“We need to be operating at every level here.

“We need to have the eyes and ears on the ground, the people who are going out looking for the cactus in the field identifying what is happening, we also need to have our scientists back in the labs trying to develop new control mechanisms and understanding how we might control and even eradicate some of these pests.”

p An electronic copy of the Opuntioid cacti best practice manual can be downloaded from

Hard copy manuals will be available from December and can be ordered by calling  9368 3333.