New information about pasture dieback and the role a humble mealybug plays in this problem suggests that management is the only option if a farmer wants to turn production around.
Queensland researchers speaking at a forum in Casino last week, hosted by Local Land Services, said the issue has grown to infect a million hectares in Queensland and lately the North Coast of NSW, west into the Upper Clarence. A year ago it was confined to the coast.
In 2017 about 50,000ha were identified - all of them north of the border.
At Eden Creek via Kyogle, Terry DeLacy and Sandra Brunet are managing their way through a dieback phase that initially killed all their creeping bluegrass, locked up and ready for winter feeding. This was last February and so they employed techniques learned while running Angus on the northern Tablelands - they burnt the biomass, sprayed out broadleaf weeds and re-sowed to annual rygrass. That got cattle through the cooler months. Now they will plant a short-lived break crop before returning next year to re-establish permanent pasture. This active management is the only way forward, say those with experience in the problem.
Pasture Dieback has existed for nearly 100 years in Far North Queensland but Dr Caroline Hauxwell from Queensland University of Technology said the current problem was being exacerbated by a new variant of mealybug, with different DNA, that she described as a "biosecurity risk" to Australia.
This new variant has damaged sugar cane in Pakistan, rice in West Bengal and kikuyu in New Caledonia and the Bahamas - where the problem is a serious one.
For the majority of graziers chemical control is not practical yet the phenomenon can turn a body of feed, locked up and ready for winter grazing, into a patch-work of partially bare-soil in a matter of weeks. Without active surveillance, by the time a livestock producer notices the decline it is too late to stop the cycle.
Insecticides are available but expensive and leaves a legacy of grazing withholding periods said senior agronomist Stuart buck, who presented with fellow agronomist Polani Shadur and beef extension officer Kylie Hopkins, all from the Department of Agriculture and Fisheries at Rockhampton.
Mr Buck said wind appeared to be the primary mode of transport; the final blow to tropical grasses coming not from the sap-sucking bug - which milks sugars and trace elements from the plant - but from a secondary "bad" fungal infection or a virus, with fusarium rot the most common.
Adult mealybugs don't feed, it's only the young that debilitate the plant. Males can fly and females tend to hibernate under thatch and in the soil over winter and return to the surface come spring - at which point they breed-on again.
Dr Hauxwell pointed out pasture collapse typically takes place after a rain event, often in the autumn after summer grazing by immature mealybugs.
Where pastures have evidence of "good" root-colonising fungi, or rhizospheric endophytes, the problem is a "lot less measurable".
"There is a link back to soil health," she said, pointing out that legumes boost the good fungi and foster soil health.
For vulnerable paddocks the ramifications can be enormous, with one Central Queensland property losing 6000 hectares of best country, or 20 per cent of the whole.
While paddocks do return to health it takes time, and a shift in mindset, said Mr Buck.
Once affected broadleaf weeds can dominate. But legumes flourish along with other tolerant tropical C4 grasses like Gatton Panic and Setaria.
Tolerance of a range of pasture species, and the role of soil fertility and grazing management, are being investigated in several trials in the Northern Rivers region by Southern Cross University led by Prof. Terry Rose and Dr Helen McGregor. Further large scale demonstration sites will be carried out on volunteer commercial farms.
Mr Buck recommended intensively managed rotational grazing.
"Don't flog it, but don't allow it to produce too much biomass," he said.
"Monitor and treat weeds as they compete with nutrients and take out water. Producers who do this have a markedly improved recovery."
Burning off biomass to rid yourself of the problem is a temporary fix at best and only makes sense in a situation with low stock numbers and high biomass
However, techniques learned over the past eight years have dissipated producer panic over the problem and has shown that affected properties can manage their way through it.
"For these people Pasture Dieback has been difficult but they have better pastures now," said QDAFF beef extension officer Ms Hopkins.
"Without re-seeding you are relying on the seed bank for a comeback," said Mr Buck, emphasising the use of a fallow and weed control if re-seeding is conducted.
Having said that, it might not be Rhodes or creeping Bluegrass that comes back but undesirable species like Giant Rats Tail or Lovegrass.
"Pasture is likely to come back if properly managed," he said and pointed to one property on buffel grass country at Emerald, Qld, where forage budgeting was used to manage the grazing pressure on emerged seedlings.
However, one property in Brigalow country where grazing was managed to encourage recovery still lies barren after seven years. Now a renovation and sowing program is planned to alleviate the problem.
Prior to renovating pasture Mr Buck advises planting break crops such as chicory, lab lab, oats, forage sorghum and herbs, with appropriate fertiliser based on the specific results of a soil test, to provide high quality short term feed.
High application of nitrogen can exacerbate the mealybug problem, he said
Quality seed that has been through germ count is another excellent investment, said Ms Hopkins
"It takes effort. You can't just chuck seed out.You have to treat the pasture like a crop for reliable results," she said.
Costs shared by Dr Hauxwell from a project on Banana Station showed that an initial investment of $450/ha yielded $1700/ha gross or a profit value of $91/ha - taking land that was effectively dead to livestock and growing it into a profitable venture.
Trial work on the North Coast through Southern Cross University will also explore how temperate perennial C3 grasses like coxsfoot and fescue, more commonly seen on the tablelands, will survive coastal seasons. It is already known that C3 annual species are not susceptible to mealybug attack however more research is needed with these perennials.
