Common Names: Giant Parramatta Grass, Smutgrass, Bloomsbury Grass, Rat-tail grass

Scientific Name: Sporobolus fertilis

Where in the Succession: Low Fertility Exploiter

Giant Parramatta Grass is a summer-active perennial grass species.

It is native to the sub-continent of India as well as eastern Asia.

It thrives in tropical, subtropical, and warm-temperate landscapes, with a preference for higher rainfall regions, but is quite adaptable to drier environments.

Interestingly, Giant Parramatta Grass is one species within the Sporobolus family; another is Giant Rat’s Tail Grass, which is also causing significant issues.

In total, there are 26 species in the family, and overall, they are challenging to distinguish, with many requiring an expert to accurately identify the specific species.

What is it telling me about my landscape?

Giant Parramatta Grass is a low-fertility exploiter,  exploiters being plants that grow as a result of fertility produced by an earlier grown plant, often our accumulators.

In the case of a low-fertility exploiter, when dominating a landscape, it is often because the soil lacks essential nutrients and the balanced microbial activity to support higher-order or more favourable grass species.

Where will I find Giant Parramatta Grass growing, and why is it growing there?

Giant Parramatta Grass appears to be an opportunistic plant seeking situations with limited competition to initiate its growth and establish dominance wherever possible.

We will often find it growing or starting its journey in landscapes with the following conditions:

•  An overgrazing event that opened up an opportunity
• Limited to no organic matter
• Degraded soils, lacking fertility
• Compacted soils and/or poor soil structure

How can we manage Giant Parramatta Grass?

Giant Parramatta Grass, being a perennial plant species, makes it different from most “weeds” that people have to manage.

With most weeds being annuals, it opens up the opportunity when the season changes to assist the weed in completing its life cycle and welcoming in the next stage of succession.

However, a perennial plant species makes this even more difficult, especially in a grazing scenario, which is likely why we are now seeing more of these grass weeds take on the mantle of key weed species being managed.

• Use mechanical intervention. With low palatability, it can be challenging to achieve great results by trying to graze livestock on it. Instead, we can look to utilise machines to open up opportunities for other species, such as slashing or mulching the material. Cultivation is another option, but one that I would recommend caution around, as it will remove the plant, but it will affect your soil life as well as open up the opportunity for the seed bank of thousands of plants to have an open opportunity to take up residence across the entire area. If you are looking to use cultivation as a tool, it really needs a strong strategy for how you are going to introduce other species and have them outcompete the Giant Parramatta Grass.
• Alter our grazing. If overgrazing and selective grazing created the environment for Giant Parramatta Grass to start, we need to look to avoid keeping those conditions being continually available. Moving towards a more time-controlled grazing system will help in this regard. Additionally, like using mechanical intervention, you could utilise your livestock by increasing stocking density, supplementing with a feed source, and using the animals to impact the Giant Parramatta Grass, thereby opening up the opportunity to introduce the desired species by sowing or spreading seed on the site.
• Increase our soil organic matter. Giant Parramatta Grass often prefers environments with low organic matter and soil humus, which aligns with its role as a low-fertility exploiter in these lower successional environments. To assist in moving it to the next stage, we can consider increasing our organic matter by promoting more material onto the surface of our landscape or by bringing in external sources of organic matter to supplement the system.
• Increase our soil fungal levels. There is the thought that Giant Parramatta Grass has a preference for bacterially dominant soils and that its growth further pushes for a bacterially dominant system. Whereas, it is thought that our grazing land should have more 1:1 bacteria to fungi, if not more leaning towards a fungal dominance. To help promote healthy soil fungal levels, we could consider feeding them. Fungal foods include complex sugars, complex proteins, fish hydrolysate, biochar, humic acid, and carbon sources such as wood, paper, or cardboard.
• Increase plant diversity away from just grasses. Focusing on incorporating other plant families, such as legumes, brassicas, and herbs, can be a great way to help alter the environment that the Giant Parramatta Grass is creating, as well as to promote the bacterial-fungal relationship we discussed above.
• Fungal bio-control. The government has researched a naturally occurring crown rot fungus, Nigrospora oryzae, which has been successful in reducing the crown size of plants over time1.

How to make the most of your Giant Parramatta Grass:

• As a Soil Indicator: Very low Calcium, High Magnesium, Little humus, Low moisture, bacterially dominant soils, low soil fertility
• Livestock: Low palatability for livestock. Cattle can be trained to graze it down, but generally not willingly. Interestingly, the fertility/quality status of the plant can be observed by how readily livestock will consume it. Much like the succession changing, it will change within plants at different points, making them more or less palatable.

Original article credit to Tarwyn Park Training. Sign up to their newsletter here. 

For more information, visit NSW WeedWise.