Leucaena leucocephala: friend and foe

· Guest post by Dave Pratchett ·

Goondaloo Creek Landcare site became the focus of my Landcare volunteering in 2019, soon after we moved to Townsville. Assisting with weed control and watering in the newly planted section opposite Tech NQ, I could look upstream to an area rejuvenated through years of sustained effort. But downstream was dominated by leucaena trees, heavy with seed pods. From a local Landcare perspective, these trees are a major foe.  

I cannot help but feel partly responsible for the invasion by this particular weed species, because early in my career in Australia, I worked hard to grow it!

The establishment of leucaena as a cattle fodder in Australia was led by Dr Ray Jones and is a fascinating story. The plant contains toxic mimosine and Ray proved that ruminants can tolerate this only when they have a very specific gut bacterium; he identified the bacterium (which was then named Synergistes jonesii) and by sheer persistence, brought samples to Australia.     https://csiropedia.csiro.au/leucaena-toxicity-solution/

In the 1980s I worked with Ray running trials in the Ord River Irrigation area to determine the optimal stocking rate and plant density for finishing cattle bred on Kimberley stations. Although various problems reduced marketing potential, the value of leucaena as a fodder crop was proven spectacularly as we reached 1500 kg (5 head) per hectare. https://researchlibrary.agric.wa.gov.au/cgi/viewcontent.cgi?article=3401&context=journal_agriculture4

I noted “Leucaena seedlings are difficult to establish under dryland conditions and under irrigation. Germination and emergence are usually not a problem, provided the seed is treated with hot water to break dormancy. Once the seedlings are two to three centimetres high, growth slows down and weeds can compete with and smother them’.

No one has boiled the seeds of the leucaena plants which have now invaded much of Northern Australia and they establish particularly well along river banks, and in cleared areas. The species is however a useful fodder plant cultivated by cattle producers in parts of Queensland, including our local area. It is also a ‘friend’ to many in  its native South America and countries such as Indonesia and India, where leucaena is a valuable dryland fodder and has an amazing variety of other uses, including human nutrition. http://archive.unu.edu/unupress/food/8F163e/8F163E08.htm

So, like all weeds, leucaena is a problem only when it invades areas where it is not wanted. It is certainly not wanted on our Landcare sites and I look forward to spending my later years in Australia working with Coastal Dry Tropics Landcare volunteers to reduce the damage it has caused here.