After 12 years of research, Australia’s northern cattle industry is finally within sight of having commercial access to a new psyllid-resistant variety of Leucaena. But how does the new variety stand up in grazing trials?

All palatable varieties of the fodder legume are susceptible to attack from psyllids, which has prevented its establishment in more humid northern environments. Even in the drier 600-800mm rainfall zones where existing Leucaena varieties can be successfully grown, psyllids can still cause production losses during the wetter months of 20-50%.

Leucaena has been well proven as a highly productive feedbase for producers in the 200,000 hectares of country where it has been successfully established – predominantly in Central Queensland, with plantings stretching from near Cooktown in the north to Goondiwindi in the south.

The ability to produce a variety that can withstand psyllid pressure and therefore be used in a much wider area of the north is considered one of the most achievable ways to boost northern cattle industry productivity.

That has been the focus for several years of researchers at the University of Queensland, who, with MLA funding, have been trialing and cross breeding a range of varieties, in the search for the best combination of psyllid resistance, protein levels, yield and digestibility.

Their efforts resulted in the final selection by MLA earlier this year of a new variety called Redlands, a hybrid comprising 90% Leucaena leucocephala and around 10% Leucaena Pallida.

Leucocephala varieties such as Cunningham and Wondergraze are known to be highly palatable, while the less palatable Pallida brings higher mimosine content, which deters psyllids, to the hybrid.

MLA says lab tests have shown that Redlands has similar protein levels and digestibility to currently available commercial lines.

“The psyllid resistance properties of the new variety should increase available feed, available protein and production in psyllid-prone regions,” MLA’s General Manager of On Farm Innovation & Adoption, Dr Matthew McDonagh said.

“We estimate that the new variety could open up a further 1.5 million hectares of Queensland to potential Leucaena production, as well as significant areas of the Northern Territory, which could in turn produce a net benefit to the industry of $500 million or more per year.”

MLA has awarded seed growing contracts to two separate landholders in Central Queensland – Carnarvon Pastoral Company and Leucseeds – and expects to have commercial volumes of seed available for purchase within three years.

Palatability/grazing trials?

While the new variety is reported to produce vigorous, high-yielding leaf production, which should make it suitable for grazing, how does it perform in actual practical grazing trials in the paddock?

Key questions which have yet to be conclusively answered include whether cattle will select and eat the new variety in paddock conditions, and how it will perform on a liveweight gain basis.

The new variety contains mimosine to deter psyllids, but if that higher content also deters cattle – as full Pallida varieties tend to do – there would be obvious issues.

In response to Beef Central’s questions about the extent of grazing trials conducted so far, MLA said it has initially contracted a small palatability/preference trial to assess the palatability and psyllid tolerance of Redlands relative to Cunningham and Wondergraze at a Producer Demonstration Site (PDS) at Whitewater Station neat Mount Surprise in North Queensland.

MLA said the trial began in July 2014 and the palatability component will run until at least July 2016, with the final report due in December 2017 (ahead of the anticipated commercial release of Redlands seed some time in 2018).

Beef Central’s follow-up inquiries have indicated that the Whitewater Station trial has so far only involved four days of actual grazing of Redlands and other varieties by a mob of weaners on a one hectare site.

Asked if that was the case, MLA said the initial palatability trial has involved a one hectare plot to assess the palatability of the new Leucaena lines bred specifically for psyllid-resistance, at both low stocking pressure and higher stocking rates.

It said the new Redlands variety has been performing well under psyllid attack, particularly when compared to the Cunningham and Wondergraze varieties.

“In the palatability trial – at lower stocking rates all varieties were grazed; however the weaners had an initial preference to Cunningham and Wondergraze,” MLA said.

“At higher stocking rates all varieties were grazed at a similar rate. The amount remaining on each plant after grazing was also similar.

“Redlands was readily and almost completely eaten, demonstrating no palatability problems.”

A four-day, one hectare palatability trial is a limited validation of a new variety that is set for mass release to landholders as soon as sufficient volumes of seed are available.

Asked if further grazing trial work is likely, MLA told Beef Central it is currently considering several further R&D investments to demonstrate productivity and weight gain of the new Redlands variety, including looking at live weight gains under extensive grazing conditions over time.

“MLA is committed to the new psyllid-resistant variety and is exploring the leveraging opportunities of existing work into Leucaena palatability,” it said.

“Given the current limitation of the seed available, competing research projects and available funding, MLA is now considering what will be the most effective research trials on the new psyllid-resistant variety to pursue, going forward.

“Discussions regarding potential research designs for this trial are underway.”

In further information supplied today, MLA said the breeding lines of the Redlands variety are made up of 87.5% of an existing highly palatable commercial variety and 12.5% of the Pallida variety.

“Previous long-term cattle grazing trails on the Redlands breeding lines have been conducted by the University of Queensland. These trials show that the long-term acceptability and palatability of the Redlands breeding lines are the same as another palatable commercial variety over four months with long-term voluntary intake and digestibility also comparable,” MLA said.

“Other international research demonstrates that Pallida content of over 50% of the diet has not reduced feed intake or growth performance in livestock.”