Chemical Free Weed Management
With uncertainty about the safety of using chemicals to control weeds, there is an increasing desire for chemical free weed management.
Some of the alternatives to chemical weed control that have been developed which Dragonfly have been implementing are:
- Thermal Weeding
- Physical removal
- Habitat removal and alteration
Thermal weeding is a method where high temperatures are applied to weeds, causing the plant to die. Thermal weeding is particularly useful in situations where conservation or health considerations are high and weed density is low such as waterways where herbicide use is not permitted.
Best results are obtained when follow up weed control is undertaken 4-6 weeks after treatment. In addition, weed control should be conducted periodically after that for example to control weeds over a period of a year it is likely that between 3-5 applications will be necessary, depending on rainfall and the extent of the weed seed bank.
This method is most effective on young annual weeds and least effective on older perennial weeds. In some cases control of perennial weeds will be ineffective however this depends on the species present and its age.
There are several thermal methods that can be used to control weeds:
- Flame weeding
- Steam weeding
- Bio-thermal weeding
A flame weeder uses LP gas to produce a flame which produces enough heat to vaporise the water in plant cells. As a result, this moisture loss inhibits photosynthesis killing the weed. A flame weeder has also been shown to stimulate the germination of native plants, while killing the seeds of annual weeds such as Devils Pitchfork, Bidens pilosa. The only disadvantage to flame weeding is the cost of gas and the risk of fire.
A steam weeder works by causing the temperature of water in plant cells to rise causing the cells to rupture. This causes the plant to dies from the outside back to the root system. Steam weeding has been shown to be more effective at killing plants than flame weeding. However, they require a lot of water and energy to heat the water.
Physical removal of weeds is the control of weeds by either:
- Hand/manual removal
- Removal by animals e.g. chickens, goats, guinea pigs and bush Turkeys
- Mechanical removal
Hand weeding is useful where there is a sparse covering of weeds or where weeds are growing with desirable vegetation that is sensitive to herbicide.
Habitat Removal and Alteration
Covering and removing weed habitat can be achieved by:
- Barriers including: mulching, on-site composting – high heat black plastic and shade
- Planting: using pioneer plants and densely growing species to out reduce habitat for weed species.
Mulching of garden beds, with materials such as crushed sandstone reduce the likelihood of weeds growing vigorously. However, the weeds will still grow so on-going mulching is required (stone or wood).
Locally native species with dense growth can be planted to reduce habitat and outcompete common herbaceous weeds and grasses.
This method is most effective with maintenance such as hand removal of grass weeds from densely planted areas to assist in the natural spread of native plants. In addition, mulch can be used to suppress weed growth in areas while the native species establish.
Other Lesser Known Techniques
High pressure water blasting method is a method for removing weeds by damaging, cutting and tearing their leaves and steams.
Foamstream is biodegradable foam made from natural plant oils and sugars applied to weeds together with hot water. The foam acts as a blanket, keeping the heat on the weed long enough to kill it. A wetting agent in the foam speeds up the transfer of heat into the weed’s cell walls.
Sugar, Salts and Pine Oil
Weed management by adding sugar, salts and substances such as pine oil to soil are in trial stages. Research has shown that adding these substances to soil increases carbon which in turn increases microbial populations and CO2 production while reducing soil nitrogen. Since these characteristics are generally more beneficial to native Australian species over exotic species, it gives native species an advantage to outcompete exotic species. Data from tests are being collected both formally and informally through experiments by councils, contractors and others.
Techniques Which May Become Commercially Viable in the Future
- Microwave – the microwaves cause water molecules to vibrate rapidly and explode the cells. Microwave action has been shown to kill weeds and seeds
- UV radiation
- Far-infrared lasers – cut stems and can be used to weaken plants overtime or to cut aquatic weeds prior to submerging them
- Freezing – using liquid nitrogen has a similar effect to steam weeding but current technology uses 2-6 times more energy