Why weed control?

We are Positive folk!!!! and still, we say that there is little value in weeds. Weed overall have a significant negative impact across the Landscape. Be Positive you say! - Maybe some introduced plants are a limited food source for native species and in some cases, the weed's ability to stabilise soil and prevent erosion is of benefit! But remember last centuries poor land management practices have often been the cause of exposed mineral earth (sand). In addition, food sources are only required as native species that once relied upon native flora (now depleted) look for an alternate diet.

Weeds harm our natural landscapes and the structure of native ecosystems. They can also contribute to land degradation and reduce the value of the natural environment; they compete for the limited resources (soil and water) A significant weed burden has so many negative flow-on effects for our native species, flora and fauna, starting with invertebrates and pollinators up to the apex predators.

Weed control

The primary focus for the Native Vegetation Grant funding for both 16:6 and Section 13 was aimed at managing weed species across the Heritage Agreement. This includes Weeds of National Significance (WoNS), Declared State SA Weeds and any weeds that compete with or impact Native Vegetation and associated habitats.

For our Grant funding and in line with our own projections the management of weeds is on track, however, it is an ongoing project with seasonal and climatic changes really influencing how we progress.

What are WoNS

Weeds of National Significance (WoNS) is a list of the most problematic plant species in Australia as determined by the federal government. Initially, a list of 20 taxa were listed and given a rank based on invasiveness, impacts, potential for spread, and socioeconomic and environmental values

Wheel Cactus - Carrichtera annua - is a Weed of National Significance

During the grant period (Approved October 2023 to December 2024), we have been actively developing and working on weed control. While we at 16:6 have been delivering on-ground work ( about 30 hours over that period ), Professionals Andrew and Janet from Irongrass Environmental Rehabilitation Services received grant funding for on-ground weed control to manage Declared species and species with heavy infestations. From Onion Weed and Hore Hound on Section 13 to Significant weeds, Boxthorn and Wheel cactus on the 16:6 Heritage Trust lands.

Andrew and Janet's knowledge and management of declared weeds is excellent, and they balance this with their understanding of the environment, plant identification, and overall habitat protection.

The extent of the Onion weed Asphodelus fistulosus - infestation in section 13- image before control starts

GPS and flagging Boxthorn in secluded locations for follow-up

IRONGRASS - Image of weed mapping on Section 13, plotted when Janet and Andrew have been spraying (onion weed and Horehound)

Early intervention seems to be the key to addressing small infestations or emerging weed threats. We have been managing Wheel Cactus this way as well as Gazanias Gazania spp and Patterson's Curse Echium plantagineum images below).

More heavily established weeds such as Onion weed, Horehound and Boxthorn follow a similar process however as well established require far more resources and focus

Training and online property weed management planning as well as SA Government PIRSA and Landscape Board advice have led us to have this approach to weed management.

1. Identify and map weeds. (refer to the Blog on mapping for additional information)

2. Obtain best practices for control/management.

3. Treat weeds when young ( not flowered or formed seed)

4. Manage weeds in a way that does not harm off-target native species (flora/fauna)

5. Follow-up controls ( ongoing monitoring and continue)

The weed control methods that have been used are:

Hand pulling – seedlings and plants that don’t have deep tap roots, especially after rain when soil is soft or in sandy areas.

Along with hand pulling - Grubbing and digging out – Spade/Mattock -is useful for smaller Wheel cacti in sandy soils.

Herbicides- The use of herbicides is our primary process for the larger infestations, from spot spraying ( Onion weed and Horehound) or cutting and painting (box thorn) and basal barking (Wheel Cactus). We also have the equipment ( drenching needle) for wheel cactus to stem inject.

Image cut and paint/paste for boxthorn control

Biological control – There is evidence in the wheel cactus of biological controls as while our infestation is not heavy areas of Cactus in the region are thick and it appears that a release of Cochineal and Cactoblastis has been undertaken at some time. Most of the larger cacti on 16:6 have evidence of bug attacks, or caterpillars ( webby filaments and die back)

Image of biological control in Wheel cactus - Opuntia robusta

Slashing – While this is not the best method locals have used it in areas with very heavy infestation. This is removing seed heads when not fully formed and removing much of the living (photosynthesizing) green parts using a handheld petrol slasher. This can assist with longer-term management by reducing the effectiveness of regeneration as well as stressing the plant. In addition when the bulk of the material is on the ground and dead it is easier to identify the new growth and target with spray. We only use this method when the plant has not yet formed seeds.

So what weed do we have across the heritage agreements

This is not a complete list, however, the weeds that we have identified across 16:6 include:

African boxthorn - Lycium ferocissimum WoNS ( A significant problem across 16:6)

Common Stork's bill – Erodiumcicutarium spp ( Uncommon only on 227 - easily managed)

False sow thistle – Reichardia spp ( Uncommon across HA individual plants easily managed)

Gazania- Gazania spp ( Uncommon across HA individual plants easily managed)

Guilford grass -Romulea spp (Widespread – Can not be easily managed)

Horehound – Marrubium vulgare ( Very common, Sec 13 and areas 227 -ongoing management)

Mallee Catchfly – Silene apetala ( present on Sec 249, Sec 13 and 215 generally low impact)

Onion weed - Asphodelus fistulosus ( Very common, on all sections other than 249 and 226 ongoing management – likely the plant most associated with soil disturbance, wombats, sand drift vehicle passage etc )

Pattersons Curse – Echium plantagineum ( Uncommon across HA individual plants easily managed)

Saffron thistle – Carthamus lanatus ( Uncommon across HA individual plants easily managed)

Thread Iris - Moraea setifolia (Widespread – Can not be easily managed)

Wild Turnip – Brassica rapa ssp (Widespread – not heavy infestation - Can not be easily managed)

Wards Weed – Carrichtera annua (Widespread – Can not be easily managed)

Wheel Cactus – Opuntia robusta WoNS ( a Few have been identified and GPS. Addressing over 2024-2026)

Wild Sage - Salvia verbenaca ( Very common, on 227 and Sec 13- uncommon on 226 and 215 ongoing management)

Please note that two specific weeds - African boxthorn - Lycium ferocissimum and Wheel Cactus – Opuntia robusta - Are the focus of much of our attention. These will be the topic of future,' Blog posts' to updates on their impact and our management outcomes.

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Other Weed species identified across the Heritage Agreement include plant species that are quite beautiful. With such attractive plants or plants with edible fruits, it is easy to understand how some species brought into the country as garden plants have escaped into our environment.

Other environmental weeds have been transported by poor land management practices such as unintentional movement with livestock and grains when transitioning between properties, and some weeds even attributed to off-road vehicles or campers spreading weeds or seeds when moving through different environments.

Disposal of weeds once they have been pulled or removed

We have tried a few different methods of disposal of weeds

1- Piling and burning. This seems to work well to completely dispose of all weeds and viable seed, however, it is limited only to a set season and often not coinciding with our fire danger season restrictions - It also means possibly transporting weeds which is not always a sound biosecurity concept, as we may move seeds from one site across uninfected areas.

This was a suggested method to dispose of wheel cactus - however, we found that even extremely hot fires struggled with the fleshy liquid-filled pads (Called Nopals).

2- Piling and composting on-site. This is good for when you have a large amount of weed to get rid of and don’t need to leave the property. We tried this for about 400 kg of Onion weed, Horehound wild turnip and sage. We piled the weeds, covered in plastic, covered in Tarpaulins and pinned them down. When all was composted, we burnt the remaining dried materials. It was an effective and seemingly good outcome with no remaining viable seeds and weeds. However, it was extremely time-consuming and took over 24 months to dispose of that one pile.

3- Placing weeds pulled, into heavy-duty plastic bags - composted down, then placed into the Council's green fill. We spoke with the council on this, and it works.... but again necessitates transporting weeds maybe across areas that have no weeds of that species. And whilst very well bagged it is a risk that should be considered.

In addition, Council Green Waste do limit what weeds can be placed into their green bins for management ie WoNS can not be placed in green fill. This is our least favoured option.

For this Grant interim, the Management of weeds is on track, however it is an ongoing project.

Why are there so many weeds?

Weed species identified across the Heritage Agreement include plant species that are quite beautiful.

With such attractive plants or plants with edible fruits, it is easy to understand how some species brought into the country as garden plants have escaped into our environment.