The cheapest weed control option is obviously prevention. There are many practices that we can adopt to ensure we do not introduce weeds onto our property.  There are 6 principles of weed management:1. Awareness – be aware of potential and existing weed problems.

2. Detection – look for any new weed infestations before they become too large or widespread.

3. Planning – Prioritise the treatment of weeds, what weeds threaten the profitability of your grazing    enterprise the most e.g. lippia, creeping lantana.

4. Prevention – far better than a cure, a $100/hour for a contractor to clean down seed laden machinery is much cheaper than any 20 litre drum of chemical.   Another example is feeding hay and grain only in designated areas to reduce risk of new ween introduction.

5. Intervene – Do it early this keeps a potentially large problem manageable.

6. Control and monitor – any weed needs to be monitored after control to ensure success.  

The rising cost of chemicals coupled with uncertainty about safety prompt many to think about any alternative weed control that is available.  Depending on the situation though, for any type of weed control it is usually a combination of controls that will be the most efficient way to deal with the problem.  A good case in point is Lantana control where large infestations are removed mechanically or by fire and the resultant regrowth is treated by chemicals and any new seedlings can be removed by hand over time.  Much of the alternative weed control technology has been developed for cropping situations and may not be applicable to woody weed treatment.  Mechanical control is the most obvious means of non-chemical weed control but is not covered here.

Some of the alternatives to chemical weed control that have been developed are:

• Flame weeding
• Steam weeding
• Oil based herbicides
• Vinegar
• UV treatment
• Soil fertility management
• Animal/species management

Flame weeding uses LP gas as a direct flame or an infrared burner to contact plants and produce heat that will vaporise water in the plant cells.  This allows moistures loss from the plants and inhibits photosynthesis.  To test if the flame weeding has been successful, squeeze a treated leaf between a your thumb and finger and if a visible thumbprint remains it indicates that weed has been subjected to sufficient heat and should be dead within three days.  Flame weeders are commonly used in horticulture on tractors mounted units.  Handheld wands are also available for individual plants.  The main disadvantage of flame weeding is the danger of fire and cost of gas.

Steam weeding has been used in many horticultural applications.  Steam has the advantage of being more effective at killing plants than flame weeding.  Generally though steam weeders require significant energy inputs to heat the water and they can require significant amounts of water. 

Vinegar (Acetic acid) has been found to be useful herbicide for broadleaf weeds and grasses.  Generally the acetic acid content in vinegar is about 5% but a level of 10% is needed to treat most weeds.  One proprietary brand also has 4% salt with the acetic acid.  Trials have shown that 10-20 concentrations of vinegar are effective on broadleaf weed but less successful on grasses. While vinegar may seem to be innocuous, at a concentration of 10% acetic acid it will cause skin irritation, have fumes and can cause eye irritation/damage.

Oil based Herbicides are based primarily on pine oil.  These sprays remove the outer wax layer of the plant causing it to dehydrate.  These sprays also reduce the viability of any weed seeds in the soil that are contacted by the spray.  Some of these sprays are registered for use in organic farms.  Application times and methods differ from other common herbicides so this must be taken into considerations when using the product.

UV treatment using Ultra violet light is being used in Europe as a weed control method and may have applications here as the science and practicalities of the method are further developed.

Soil management can affect the number and type of weeds that we have.  There are a number of publications that indicate the soil conditions that can favour particular types of plants.  Some weeds such as African Lovegrass have the ability to grow over a huge range of soil types but other weeds can have specific soil requirements such as low Calcium or phosphorus.  A soil test and a change in soil fertility based on the soil test may be the easiest option to control some weeds.

Animal management or variation in grazing species can be a useful management tool. Camels and goats have been used with success in controlling some weeds but are they more difficult to manage than the weed.  This would need to be seriously investigated before adopting this type of weed management.

Before we try to control any weed it is important to ask;

1. Is the weed a threat to productivity, health or the environment.
2. Is the weed costing more to control than it is worth.
3. Is the weed a symptom of dry seasons or overstocking.
4. Is the weed Declared and required to be controlled by law? 

More information from:
www.richgro.com.au   vinegar/salt herbicide
www.acaengineering.com.au   steam weeders
www.certifiedorganics.info  Pine oil based herbicide
www.gameco.com.au  flame weeders

Acknowledgement

This article is courtesy of the Queensland Primary Industries and Fisheries - Beeftalk magazine.