LAST week I very briefly mentioned withholding periods in relation to herbicide use.
For those working the land this concept is mostly well understood but for the smaller landholder withholding periods and other label restrictions may be a source of confusion so I’ve chosen to this week cover giant rats tail grasses (GRT).
GRT grasses (Sporobolus pyramidalis and Sporobolus natalensis) are not only very common in our region but have as one of their main treatment options a good example of a herbicide with a more complex set of restrictions than most.
GRT grasses are category 3 restricted invasive plants under the Biosecurity Act 2014 and carry that general biosecurity obligation for landholders to take all reasonable and practical measures to minimise the biosecurity risks associated with them along with whatever requirements your local authorities are enforcing.
They can be hard to tell apart from other common pasture grasses when young especially in comparison to some native Sporobolus although the natives will, when mature, be shorter with softer leaves, less dense seed heads and have obvious hairs at leaf margins that the introduced grasses lack.
They are also very similar in appearance to the other introduced and invasive category 3 restricted Sporobolus grasses, American rat’s tail grass (Sporobolus jacquemontii) and giant Parramatta grass (Sporobolus fertilis).
I won’t waste space here going over all the finer details of telling these apart as it gets very difficult and detailed and ultimately in our region if you’ve eliminated it being a native your most likely encountering GRT and if it is one of the other two then you should be controlling it anyway.
If you need positive identification to formulate your control plan which for Sporobolus can vary greatly your local Council will help with ID or you can always send a sample to the Queensland Herbarium.
GRT are tough grasses, rough on teeth and with very little nutrient value so when present in pasture in high concentrations can result in a lot of hard chewing for little growth.
The best defences against GRT are a healthy population of desirable plants that can out-compete the weedy species and limiting seed entering your property.Overgrazing, a lack of nutrition in or disturbance of the soil give GRT the opportunity to become established.
Each mature plant can produce 85,000 seeds annually which are easily moved by domestic or feral animals either on the body or in the gut as a good percentage will survive being ingested and passed out as much as a week later. The seeds also have the ability to last as long as 10 years in the soil and get very sticky when wet so adhere really well to anything moving through them whether that be animals or machinery.
Vehicle and machine hygiene are critical when moving between affected and clear areas as is limiting access to your property.
People should keep this in mind if you’re ever wondering why farmers get so protective of people coming onto their land unannounced.
GRT control programs can become very complex incorporating several non-herbicide practices but in general they will include some level of herbicide application.
My favourite methodology for lighter infestations is spot spraying with Glyphosate after first having manually removed seed heads. Most of my work is either small property or in commercial easements for utility managers through landholdings where the owner does not want his or her grazing options affected by our activities and Glyphosate has no withholding period.
It is important to cut off, bag and burn seed heads where they are present and careful spraying on foot rather than from the seat of a ute or quad will minimise overspray limiting new bare patches which only lead to more weed seed germination.
Wiping, which involves pulling a boom fitted with either absorbent pads or wick like rope material saturated with a high concentration Glyphosate mix through the GRT, can be very effective where density is too great for hand spraying to be viable.
The boom needs to be set at the correct height to contact the GRT and avoid the shorter non-target species. Poor separation between them or uneven surfaces can make this practice difficult resulting in off target damage and most often multiple applications will be required but done well in the right location it is a good option.
Lastly, we come to the application of Flupropanate-based herbicides. There are liquid and granular formulations available with the granular being suitable for both hand (using a spreader) and aerial application including through treed areas.
It is mostly root absorbed so it will wash off the plant in the first rain following treatment to penetrate the soil surrounding the roots so generally no surfactant is required and definitely not wanted if the surfactant you have in hand has any ‘sticker’ properties.
Flupropanate is very persistent and will provide some ongoing control of seeds germinating in treated areas. This is why it is such an important tool for heavy and/or wide spread infestations. One of its main advantages over Glyphosate spraying is that it is less likely to damage surrounding desirable species. It also has the capacity to control other invasive species like serrated tussock, African lovegrass, and many more.
It is quite slow acting so if spot spraying I will often use a Flupropanate -Glyphosate mix to provide the faster knockdown of Glyphosate and the residual action of the Flupropanate.  This persistence however is also its main drawback for some. Because of it there are a complex set of restrictions associated with its use. If spot spraying there can be no grazing or collection of feed for 14 days and if doing other broad scale spraying this period jumps to four months.
Additionally, once stock have been allowed back into the treated area then in both cases they need to be moved to untreated areas for 14 days before meat or milk is collected and this restriction applies permanently. I strongly recommend taking careful consideration of your options and formulating a long-term plan before embarking on a major GRT control program – it is one of the worst weeds we have.