Rat’s tail grasses

Sporobolus pyramidalis, S. natalensis, S. fertilis, and S. jacquemontii

Rat’s tail grasses are a group of exotic grasses with similar characteristics which are listed as priority invasive plants for the Sunshine Coast region. They include common giant rat’s tail grass, Sporobolus pyramidalis and S. natalensis, giant Parramatta grass, S. fertilis and American rat’s tail grass, S. jacquemontii. Council notes the management objective for these species is: “Land managers should reduce the impact of these species and stop their spread across the landscape.” These grasses are category 3 restricted invasive plants under the Biosecurity Act 2014. We must not release these invasive plants into the environment, give away or sell seed, plants or something infested with its seeds. The Act requires us to take all reasonable and practical measures to minimise the biosecurity risks associated with invasive plants under our control. Further information on these grasses can be found here: Rat’s tail grasses.

Information and Identification

These grasses were introduced to Australia for trials for pasture grasses and soil conservation. As they are tough and well-suited to our climate, as well as being very successful reproducers, they have spread extensively throughout northern, eastern and southern Australia. They are not very palatable to stock when mature, as the grass blades are difficult to chew (and cut!) and they grow very well in degraded pastures, so they tend to out-compete other pasture grasses and come to dominate poorly managed pastures. They can produce up to 80,000 seeds per square metre, with viability of up to 90%, and the seeds can persist in the soil for up to 10 years – all of which make it a very successful weed! There are a number of native Sporobolus species, too. These tend to be smaller, with less dense seed heads and hairs at the leaf junctions:

Identification:

• These grasses form robust perennial tussocks up to 2m tall.
• The seed heads form a “rat’s tail” when immature, but in some species these open out into a pyramidal shape on maturity.
• Some species have a distinctive sooty mold on the seed heads, making them appear black.
• The grass blades appear to be a soft green, but can be distinguished from most other pasture grasses by their toughness – if you take a blade between your hands and twist it repeatedly, it’s hard to break. You’ll see where a mower or brushcutter has been – the tussocks of these grasses don’t get cut, they just turn into a twisted fibrous mess.

Impacts

Economic

• Can come to dominate pastures, particularly after overgrazing or soil disturbance.
• Can reduce carrying capacity of pastures.
• Can increase wear on the teeth of stock.

Environmental

Can degrade natural areas by reducing ecosystem values and habitat for native fauna.

Distribution at Crystal Waters

Rat’s tail grasses are widespread at Crystal Waters. Back in 2000 it was reported that there was a major infestation in Grey Gum paddock and despite numerous control efforts, that patch is still there. The other major area of infestation is in the paddock above Lot 21, as well as throughout the area around Lots 14-23, right down to the Kilcoy Lane fence. Smaller patches can be found on most of the main fire trails, with scattered plants in most other grassy areas. It does not seem to occur in most areas dominated by native vegetation.

Control methods and efforts

Detailed information on control methods can be found in the link given above about these grasses. It’s important to note that there is no simple answer for controlling these grasses. Treatment with herbicides is only likely to be successful if it is followed up with further treatments and with restoration of the pasture or cropping. None of the recommended herbicide treatments can be used here, and most of the recommendations for limiting spread are simply not practical here. Recommendations such as washing down machinery to limit spread, and limiting movements of stock to prevent spread just won’t work here, where we have dozens of vehicles potentially spreading seed along the roadsides and hundreds of kangaroos and wallabies moving around the property, as well as deer.

Some years we have tried to remove seed heads in the main areas of infestation before they are slashed, to reduce the amount being spread, but there is little evidence that this was successful. In Grey Gum the Dairy group is attempting to limit the spread by removing seed heads, and some tussocks, especially around the boundaries of the paddocks and in high traffic areas.

In paddocks the best control method seems to be to promote healthy growth of other grass species, so that there is little room for new rat’s tail grasses to germinate. In areas where we want to maintain turf (roadsides and spillways) we probably need to remove existing tussocks (there aren’t many) and keep the turf healthy to prevent germination of rat’s tail grasses.