Updated: Feb 13
... and other weeds
The Australian bush is under constant threat of invastion from weeds of all types. There are a number on Istari including camphor laurel, moth vine, mist flower, crofton weed, lantana, mickey mouse plant, senna and cats claw creeper vine to name a few. It is a long list!
Cats claw (Dolichandra unguis-cati) is one of the worst of the environmental weeds found in this region. It gets its name from the claw like tendril which attaches to the host vegetation, enabling it to climb and run up the trees.
This South American vine loves the sub tropical climate of the Clarence valley and thrives along the banks of its creeks and rivers, gradually covering the trees and eventually killing them by smothering or causing the tree to fall over from the weight of the vine.
Spring is flowering time for cats claw. The yellow flowers and prolific growth made it common in gardens earlier last century but unfortunately it forms a multitude of long seed pods releasing thousands of seeds with feather like wings to drift on air and water. These seeds sprout forming a carpet across the ground choking anything else from coming up.
Driving up the Clarence valley during spring you can see the extent of the infestation in the valley as the plants display their yellow trumpet flowers. Our infestation started along a major creek on our boundary which has now spread up stream of the larger creek and into the smaller creeks and gullies.
Spreading cats claw
Cats claw is very difficult to manage. Each new plant produces a tuber. One small tuber at first but as it grows it sends runners across the ground on their inevitable quest for something to climb up. At intervals it sends out extra roots for new tubers to grow, usually forming a chain of many tubers. These tubers can grow to the size of a very large sweet potato!
When the vine reaches a taller plant it grows up the plant looking for light. Trees become the ideal place for the vines to grow quickly running up and eventually smothering the host plant. When they get big enough to reach the tops of the trees, they flower and seed. The seeds drift down around a large area around the tree. Sometimes the seeds fall into water which are easily transported, floating on the water.
Cats claw control
Cats claw is considered an environmental weed. It doesn't harm cattle or other domestic livestock but covers the trees eventually killing them. Cattle will eat the vine however, as cats claw grows along streams banks, the cattle are clambering up and down banks causing their own damage to the waterway. In some cases the cattle may keep the cats claw down but only on the ground. Cats claw that makes it up the tree will continue to cover the tree, producing large amounts of seed spreading the weed further.
There are no native biological controls although some imported insects are being tested at the moment. These trials have been concentrated in south east Queensland and now in northern NSW. There is little specific information on the progress of these trials but you can check out the websites below outlining these possible biological controls. This method of control will not kill the cats claw already established, only slow its spread.
As the plant grows the vine's stem will grow and can get to plate size diameter in the extreme! At this size they can look like a tree trunk, not a vine, especially if their original support has died, leaving the vine stem standing independently. The vine is relatively soft so can be easily cut but at this size it is best cut with a chainsaw.
Alternatively a hole can be drilled into the vine, making sure it doesn't go through to the tree, then the herbicide is injected into the hole.
Cutting the vine at the base of the tree will, of course, kill the upper parts of the plant but will not kill the plant. The cut vines will quickly re-shoot sending many runners back up the tree. This can happen in less than a season!
We have tried pulling the tubers out, cutting the bases and finally poisoning. Poisoning is the only way we have found to control this weed with any real effect.
We dislike using herbicides. In fact we tried to not use it for many years. One season was spent sitting on the forest floor pulling out the small plants. This took ages and given the many hectares of infestation would never provide a control. If you have a very small infestation you may be able to remove it by hand but otherwise physical removal just doesn't work.
There are a couple of herbicides which are effective on cats claw but glyphosate is the most common one used. Glyphosate was initially marketed under the name Roundup but there are many brand names with the same ingredient. Some also indicate the concentration of the herbicide, like 360 which indicates 360g/litre of glyphosate. Although this is a very common poison used in agriculture there may be health issues associated with its use - see some links below for more information on this.
All precautions should be taken when using this or any herbicide. Always wear gloves when handling the chemical. Ensure you are suitably dressed with a long sleeved shirt and long pants. Wear a mask if spraying. Follow the directions on the use and application. Avoid skin contact.
There are a number of ways to apply the herbicide depending on the size of the plant.
foliage spraying - spray the leaves
cut stems (larger than a pencil diameter) and paint/paste/spray cut stem with a more concentrated dose
scrape stems to remove the bark exposing the stem then paint/paste/spray scraped stem - this is helpful if the stem is difficult to cut
drill stems then inject herbicide directly into the stem - used for very large stems
Glyphosate is a foliar herbicide. It is absorbed through the leaves when the herbicide is directly sprayed on the foliage. Once absorbed it inhibits a plant enzyme which in turn stops a growing process within the plant, eventually killing the plant. This may take some time, usually many weeks, to see results.
The photos above show patches which took five to six weeks to completely kill the plants sprayed. Even then some will survive and will need follow up, spot spraying the surviving cats claw.
The poison is most effective on a growing plant, particularly the growing tips which are reddish, so winter and dry periods are not recommended times for foliar spraying but I have sprayed in winter with some success. It will take some hours for the plant to absorb the poison so don't spray if it is going to rain. It will need at least several hours after the application to be effective.
Glyphosate is non specific so will affect all plants (except for some genetically modified plants specifically designed to not be affected by glyphosate). Spraying must be done with care. Don't spray on windy or even breezy days as you can't control where the mist drifts which may kill wanted native plants.
As a non specific herbicide it is difficult to spray the cats claw when already smothering low bushes like young trees, lomandras and ferns. Take extra care in these situations. We try to spot spray directly on the cats claw leaves, avoiding the leaves of the covered native plant. You can sometimes pull off some of the vine and spray it away from the covered plant. When cats claw infests ferns like forest fern, try to spray below the fern leaves where the cats claw is close to the ground. Dark stems won't be affected by the herbicide. There will be some collateral damage to some host plants but keep in mind the cats claw will kill the plant anyway by smothering it.
Large plants with stems larger than a pencil diameter need to have a direct application of the herbicide to the cut or scraped stem. The herbicide will be taken directly into the plant rather than through the leaves. The poison must be applied within 10 -15 seconds of making the cut, scrape or drill hole as the plant will seal the cut areas after that, stopping the uptake of the herbicide. The more herbicide you can have the plant absorb the more damage it will do. We have found scraping doesn't always work on thick stems if the scrape is not large enough so cutting is best. Similarly spraying even concentrated herbicide on thin stems won't be very effective. If the stem can be split when cutting, the herbicide applied to the cut and split will be more effective.