Conquering Weeds in Spring

If you are anything like me you thought you could cope with the weeding during winter but it suddenly spirals out of control during Spring. This seems to happen every year and I am never sufficiently prepared for the inundation. So what can we do to prepare and what are the best methods for dealing with your weeds?

What is a weed?

It may be helpful to consider what we consider as weeds or invasive plants – the Australian Government’s Environment Department (EPA) defines weeds as: “any plant that requires some form of action to reduce its effect on the economy, the environment, human health and amenity.”

Weeds are often excellent at surviving and reproducing in disturbed environments and are commonly the first species to colonise and dominate in these conditions, typically producing large numbers of seeds, thus assisting their spread.

Sheep sorrel (Rumex acetosella) above is a major weed worldwide. Weeds pose a serious threat to human and animal health, to primary production and to our natural environment by reducing farm productivity, displacing native species and contributing to on-going land degradation and reducing land values. It is estimated that weed control measures cost Australian farmers $1.5 billion dollars per year and that weeds cost $2.5 billion dollars per year in lost agricultural production.

While many plants introduced into Australia in the last 200 years have become weeds, a native species that colonises and persists in an ecosystem in which it did not previously exist can also be a weed.

Responsibility

There are statutory obligations to clear declared weeds from your property and all States and Territories have their own weed lists, which are available from local Departments of Primary Industry. In Tasmania each declared weed has a statutory weed management plan that details the regulatory framework for the control and eradication of that weed under the Tasmanian Weed Management Act 1999.

While primary responsibility for managing weeds rests with landholders and land managers, collective action may be necessary if the problem is beyond the capacity of the individual to cope. Successful weed management requires a coordinated national approach, which involves all levels of government in establishing appropriate legislative, educational and co-ordination frameworks in partnership with industry, landholders and the community.

Many procedures and methods are available to manage the effects of weeds, the most effective being prevention, early detection and eradication. Once the initial infestation is controlled, follow-up monitoring and control is required to ensure that reinfestation does not occur.

Identification

Seventy-seven plants have been officially declared as weeds under the Tasmanian Weed Management Act 1999. Many weeds have similar appearances and it is important that the correct species are recognised as weeds. Tasmania’s list of weed species can be downloaded from the DPIPWE website ) and the Australian Government has a comprehensive list found here:  http://www.environment.gov.au/biodiversity/invasive/weeds/identification/index.html

Other information can be found on local government websites eg:

The Southern Tasmanian Weed Strategy is an important foundation for the practical implementation of the regional NRM Strategy. The pdf file can be downloaded here: http://www.wellingtonpark.org.au/assets/southerntasmanianweedstrategyweb.pdf

The Tamar Valley Weed Strategy is a community based organisation trying to combat the spread of weeds within the Tamar Valley region and has a comprehensive website.  http://www.weeds.asn.au/tasmanian-weeds/view-by-common-name/

The Tasmanian Herbarium provides an invaluable research service for weeds in Tasmania. Its job is to keep a record of all native and introduced species of plant in the State and to identify new or existing plants. There are regional Bushcare or Landcare groups that are very knowledgeable about local infestations and control methods.

Weed maps are also available at which show which weeds are most prevalent in an area.

Prevention

Prevention is the most effective method of dealing with weeds. Once a weed has entered an area and become established, eradication is far more expensive and it is likely that greater resources will be required to control its further spread and reduce its impact. In the home garden choosing plants that are unlikely to become weeds in your area and removing potentially weedy plants and disposing of them through approved channels is essential. Spreading mulch over soil surfaces in the garden will reduce weed growth.

On small holdings the spread of most weeds occurs through the movement of goods, animals and vehicles contaminated with weed seeds. You can reduce the risk of spreading weeds by buying certified weed free fodder and seed wherever possible. Washing down vehicles that have been in known weed infested areas also helps with pest and disease reduction. A guide is available on ;

If possible quarantine any weed infected stock or feed and monitor weed infestations and carry out control works regularly. Early detection and quick, coordinated responses are needed to eradicate or contain species before they become too widespread and control becomes technically and/or financially impossible.

Control and Management

The following options are available to control weeds: chemical, biological, physical or integrated weed management.

Chemical control:

Chemicals such as herbicides work by being absorbed by the plant thus destroying it. In some situations herbicides offer the only practical, cost-effective and selective method of managing certain weeds and by reducing the need for cultivation, they can prevent soil erosion and water loss. In most cases, weeds must be actively growing for herbicide treatments to work. Other factors to be taken into account include wind speed and direction and proximity to waterways to prevent spray drift and any possibility of rain, which will dilute the treatment.

The chemicals within herbicides function in a limited number of ways known as the mode of action, which classes chemicals according to the site or enzyme within a plant, disease, or insect that the active constituent works on eg by speeding up, stopping or changing the plant’s normal growth patterns, by desiccating the leaves or stems or by defoliating the plant. An example is the herbicide Glyphosate, which prevents the target plant making key amino acids. Mode of action is particularly important for resistance management.

As well as using different modes of action, herbicides can be classified according to how they are taken up by the plant. The main types are:

  • Contact – these kill plant tissue at or near the point of contact with the herbicide (they do not spread around the plant). Therefore, they require even coverage in their application.
  • Systemic – these move through the plant tissues via the plant’s circulation system, and can be injected into the plant.
  • Residual – these can be applied to the soil in order to kill weeds by root/shoot uptake. They remain active in the ground for a certain length of time, and can control germinating seedlings.

Herbicides also have differing selectivities, and can be categorised as either broad spectrum (working on a wide variety of plants) or selective (working on a specific range of plants).

For example some herbicides are effective on grasses, whereas others are more effective on woody weeds and will leave grasses intact to provide competition against re-establishment of the weeds.

When using a herbicide it is extremely important to read and follow the information contained on the label, which includes: the active constituent, directions for use, the withholding period, expiry date, tank mixing, resistance and storage instructions as well as other information. The label itself is a legal document, which under legislation, must be adhered to at all times. In some cases, a weed is only susceptible to one specific herbicide and it is important to use the correct product and application rate for control of that particular weed. Compatibility is very important when you are tank mixing chemicals or adding two or more together to control multiple plants with the one spray application.

Some herbicides have a period of time that must elapse before the next crop can be planted back into the treated area. Residual herbicides can have lengthy plant-back periods for particular crops, which must be adhered to in order to prevent crop damage.

The withholding period is the time that must elapse between treatment of a pesticide, and the harvest, or selling of the treated product, and is on the label to prevent higher than acceptable pesticide residues in food products.

The CAUTION denotes the poison schedule of the pesticide, which eg for Roundup CT is a SCHEDULE 5. This means it is available to the public, but requires caution in its storage, handling and use. The SCHEDULE number also indicates the type of personal protection equipment that should be worn when using this product.

More information is available on the manufacturer’s websites and from http://www.herbiguide.com.au/InformationHerbicides.aspx

Protection of crops

Protection of crop, native and other non-target plants
With all herbicides it is vital to avoid contact with foliage, green stems or fruit of crops, desirable plants and trees since severe injury or destruction may result. Do not apply under weather conditions or from spraying equipment that may cause spray to drift onto nearby susceptible plants/crops, cropping lands or pastures. Do not contaminate dams, rivers or streams with product or used container. Do not apply to weeds growing in or over water or across open bodies of water.

How to apply herbicides

Foliar spraying involves diluting the herbicide with water or another dilutent as specified on the product label, and spraying over the foliage to the point of runoff, until every leaf is wetted, but not dripping. Spraying is most efficacious on flat weeds, ground covers, grasses shrubs, and dense vines less than 6 m tall so that complete coverage is achieved. Advantages include speed and economy, but disadvantages include the potential for spray drift and off-target damage.

Basal bark spraying involves mixing an oil soluble herbicide with a dilutent recommended by the herbicide manufacturer and spraying the full circumference of the trunk or stem of the plant and is suitable for thin-barked woody weeds and undesirable trees. It is also an effective way to treat saplings, regrowth and multi-stemmed shrubs and trees. This method works by allowing the herbicide to enter underground storage organs and slowly kill the targeted weed.

Stem injection involves drilling or cutting through the bark into the sapwood tissue in the trunks of woody weeds and trees. A herbicide is immediately placed into the hole or cut within 15 seconds of drilling the hole or cutting the trunk. The aim is to reach the sapwood layer just under the bark (the cambium growth layer), which will transport the chemical throughout the plant. This method kills the tree or shrub where it stands, and only those that can be safely left to die and rot should be treated this way.

Another method referred to as the ‘drill and fill method’ or tree injection is used for trees and woody weeds with stems or trunks greater than 5 cm in circumference. A battery-powered drill is used to drill downward-angled holes into the sapwood about 5 cm apart. The placement of herbicide into the hole is usually made using a backpack reservoir and syringe that can deliver measured doses of herbicide solution.

Similarly the ‘axe cut method’ or frilling or chipping involves cutting through the bark into the sapwood tissue in the trunk, and immediately placing herbicide into the cut. This method can be used for trees and woody weeds with stems or trunks greater than 5 cm in circumference.

Cut stump application is where the plant is cut off completely at its base (no higher than 15 cm from the ground) using a chainsaw, axe, brush cutter or machete. A herbicide solution is then sprayed or painted onto the exposed surface of the cut stump emerging from the ground, with the objective of killing the stump and the root system.

Stem scraping also called bark stripping or stem painting is used for plants and vines with aerial tubers. A sharp knife is used to scrape a very thin layer of bark from a 10 cm section of stem. Herbicide is then immediately applied to the exposed soft underlying green tissue.

The wick application method uses a wick or rope soaked in herbicide from a reservoir attached to a handle to wipe or brush herbicide over the weed.

For up to date chemical products listed for a particular weed the Agricultural Pesticides and Veterinary Medicines Authority (APVMA) website provides an excellent search engine. Simply type the weed you are interested in controlling in the ‘disease/pest’ search field and hit search. The search will bring up all the products and their labels to help you determine the rate of chemical required for the job at hand. https://services.apvma.gov.au

Non Chemical Sprays

Non Chemical sprays:

Organic producers are not allowed to use synthetic pesticides in their production system. However, herbicides derived from natural sources may be allowable. Interceptor is a non-selective, contact herbicide derived from an extract of pine oil. Since the herbicide kills by contact, uniform spray deposition on the target plant is required for maximum efficacy. An evaluation of the effectiveness of this herbicide can be found at

Many organic gardeners prefer to use homemade weed killer recipes so here are two to try:

  • Put ½ cup of salt in a spray bottle and fill with 4 litres of white vinegar. Add a squirt of liquid dish soap to act as surfactant. Use early in the morning on a hot day as it works best in the heat.
  • Or combine 4 litres of 10-20% pickling vinegar with 60ml. orange oil and a squirt of dish soap. This is claimed to kill any plant and again works best on a hot sunny day. It is suggested wearing rubber gloves.

Don’t leave the mixture in your sprayer for long because it will corrode the seal so wash the sprayer thoroughly after use. The mixture can be placed on a sponge and wiped on the plants you want to kill. While the acetic acid in the vinegar will start working immediately, some weeds will have to be treated again. One advantage is that new plants can be planted the next day after treating the weeds.

Cut stump application is where the plant is cut off completely at its base (no higher than 15 cm from the ground) using a chainsaw, axe, brush cutter or machete. A herbicide solution is then sprayed or painted onto the exposed surface of the cut stump emerging from the ground, with the objective of killing the stump and the root system.

Stem scraping also called bark stripping or stem painting is used for plants and vines with aerial tubers. A sharp knife is used to scrape a very thin layer of bark from a 10 cm section of stem. Herbicide is then immediately applied to the exposed soft underlying green tissue.

The wick application method uses a wick or rope soaked in herbicide from a reservoir attached to a handle to wipe or brush herbicide over the weed.

For up to date chemical products listed for a particular weed the Agricultural Pesticides and Veterinary Medicines Authority (APVMA) website provides an excellent search engine. Simply type the weed you are interested in controlling in the ‘disease/pest’ search field and hit search. The search will bring up all the products and their labels to help you determine the rate of chemical required for the job at hand. https://services.apvma.gov.au

However, research has shown that vinegar with 20-30% or more acetic acid concentrate works differently. If the ground surrounding difficult weeds is saturated with this strong vinegar, it will lower the soil PH to levels as low as 3, which stops anything growing. Microbes and soil biota will be safe and will go dormant until the PH comes back to normal over time, unless lime is added to speed it up.

Acetic acid acts as a desiccant, burning the leaves, drawing out moisture and destroying the plants’ cell membranes. The leaves, stems and any other plant part it reaches will immediately die by simply drying and shrivelling up.

Use caution with all chemicals, handle carefully and don’t get any in your eyes. Any acetic acid concentration over 10% will also burn skin, and be especially dangerous to eyes. This harsh vinegar should only be used with tough weeds that are away from growing areas such as blackberry.

Many herbal and plant oils contain natural pesticide and herbicide properties. They can be mixed with other substances such as vinegar and soap to safely eliminate weeds. These oils are often found in organic preparations in garden shops, and include d-limonene, or citrus oil extract, Neem oil, castor oil, pine oil, cinnamon, clove and thyme oil. Cinnamon for example contains eugenol, a particularly potent herbicide. Dribble the mixture onto the weed so that it coats and smothers it.

Corn gluten is a pre-emergent weed killer and is a natural by-product of processing corn or maize into corn meal. It has an oily coating and inhibits the formation of roots. It does not harm existing plants and as a bonus has high nitrogen content, so it feeds your soil as well.

In early spring and again late summer if necessary, sprinkle over the area where weeds were or you know there are unwanted seeds. Use according to packet instructions or at 1 kg per 9.30 square metres. Wait 6 weeks before the corn gluten has completely broken down before you sow desirable seeds.

PPE

Always wear protective clothing ie long pants and sleeves, boots, gloves, mask and eye protection – especially when handling toxic weeds or using chemicals. Wash dirty clothes separately to avoid contamination.

Cleaning up after using sprays

The importance of cleaning and decontaminating spray equipment after herbicide applications cannot be over-stated. Crops and pastures have been severely damaged and destroyed by spray equipment that was not thoroughly cleaned before use. Take particular care to follow the directions on the product label for cleaning and decontaminating spray equipment.

At the least it is very important to drain and flush the tank, hoses, and boom with clean water for 10 minutes. Triple wash if necessary. Nozzles, screens and filters should be removed and cleaned separately. Rinse water should be discharged into a designated disposal area not into waterways. Some chemicals require other cleaning methods such as detergent or disinfectant. For more information see:

Biological control

Biological control is achieved by introducing some of the biological agents which control their distribution and density in their native habitats elsewhere in the world. Before exotic agents can be released into Australia they are extensively tested to make sure they are host specific i.e. only attack the weed species. Once these agents are approved by the Australian Quarantine Inspection Service they are bred up in laboratory and greenhouse conditions where they can be nurtured and monitored.

Biological control will not totally eliminate a weed but it should reduce its vigour and abundance to a level that is either tolerable or that can be managed by more conventional means. In the long term, a more natural balance between the weed and its predators is achieved. Best results have occurred when more than one agent attacks a specific weed.

A successful example of biological control is the gorse spider mite, Tetranychus lintearius, which attacks the mature foliage. First released in December 1998 it is now present at 25 sites throughout the State.

Physical Control

Physical control

The removal of weeds by hoeing, mowing, mulching, tilling, burning, grazing or by hand is a good method for selective removal of weeds without disturbing the surrounding desirable vegetation. However, it is very labour intensive and is often only used in small areas, such as gardens or in larger areas during bush regeneration. To be successful minimise disturbance, removing isolated weeds in areas of good bush and agricultural land first, rather than tackling a dense infestation. Hand-pull weeds from moist soil or after rain, then fill in holes with soil and pack down firmly. Cut and paint stems rather than pulling out large plants. Don’t pull or rip down climbers from trees as damage can occur to native or non-invasive species.

Tilling turns over the soil and buries weeds beneath the soil, providing a barrier to the sun, thus killing the weeds. Using agricultural machinery tilling can be easily undertaken over a wide area and is used for making soil ready for planting new crops. However, it can also lead to damage within the soil’s structure and exposes the soil to erosion and further invasion by weeds.

Thermal weeding using heat in various forms (radiant, flame, steam, hot water) to kill plant tissue is another option. Burning either on a large scale or with a hand burner or propane torch can be effective in the right conditions as it removes the above-soil body of the weeds killing most of the plants. Choose a time after rain or at least when any nearby plants or mulch are soggy and wet. Have a water hose handy or a watering can to dowse any sparks. If carried out before seed is set it can prevent the further spread of weeds. Burning can be undertaken over a wide area with minimal human input, however, this sort of burning also exposes the soil surface to erosion. If burning is used as a control method, caution should be exercised to minimise the risk of harm to the environment and to those undertaking the activity. Obviously windy days and high temperatures should be avoided and the availability of a water source is important as even in the home garden fire can get away quickly.
Boiling water is also effective on weeds if you only have a small area to control. This should also kill some surface un-sprouted seeds too. Be careful of your hands and feet, and keep children and pets away. Go slowly and concentrate when carrying the hot container.

A steam machine can be used to control weeds for a larger area. Precious plants should be covered up to protect them.

Soil solarisation kills weeds and can actually sterilize the soil and kill all life if hot enough. You need plenty of sun for this method to work. Transparent plastic lets the light in so will encourage the weeds to grow initially, but then they will get severely burnt by the direct sunlight, as well as allowing heat to build up under the clear plastic. Black plastic absorbs the heat, blocks the light and cooks the weeds and soil underneath.

Applying thick mulch all year round to inhibits weed growth and germination of weed seeds by blocking sunlight and light rainfall from reaching the soil surface. Using old carpet for large areas to smother weeds results in the ground being perfect the following year to plant into as the worms have done all the work turning weeds into soil. Layers of newspaper covered with a heavy mulch are also effective but again if you live in a bushfire prone area you will need to use a different method.

In the vegetable garden use companion planting to fill spare spaces with flowers and herbs with foliage that smothers weeds. This also has the advantage of attracting bees.

Learn to love your weeds

Some weeds can be delicious and may be more nutritious than store-bought greens.

The yellow petals and young leaves of dandelions can be used in salads, and the roots can be used as a coffee substitute. Sydney-based nutritionist Catherine Saxelby said most edible weeds were high in phytonutrients and phytochemicals such as beta-carotene that help protect the body against disease, as well as vitamin A, vitamin C, and minerals such as potassium. However, edible weeds do have some nutritional drawbacks as some wild leafy greens, like the sorrel varieties and purslane, have high concentrations of oxalic acid, which has been linked to kidney stones and is poisonous in very large amounts.

Thermal weeding using heat in various forms (radiant, flame, steam, hot water) to kill plant tissue is another option. Burning either on a large scale or with a hand burner or propane torch can be effective in the right conditions as it removes the above-soil body of the weeds killing most of the plants. Choose a time after rain or at least when any nearby plants or mulch are soggy and wet. Have a water hose handy or a watering can to dowse any sparks. If carried out before seed is set it can prevent the further spread of weeds. Burning can be undertaken over a wide area with minimal human input, however, this sort of burning also exposes the soil surface to erosion. If burning is used as a control method, caution should be exercised to minimise the risk of harm to the environment and to those undertaking the activity. Obviously windy days and high temperatures should be avoided and the availability of a water source is important as even in the home garden fire can get away quickly.
Boiling water is also effective on weeds if you only have a small area to control. This should also kill some surface un-sprouted seeds too. Be careful of your hands and feet, and keep children and pets away. Go slowly and concentrate when carrying the hot container.

A steam machine can be used to control weeds for a larger area. Precious plants should be covered up to protect them.

Soil solarisation kills weeds and can actually sterilize the soil and kill all life if hot enough. You need plenty of sun for this method to work. Transparent plastic lets the light in so will encourage the weeds to grow initially, but then they will get severely burnt by the direct sunlight, as well as allowing heat to build up under the clear plastic. Black plastic absorbs the heat, blocks the light and cooks the weeds and soil underneath.

Applying thick mulch all year round to inhibits weed growth and germination of weed seeds by blocking sunlight and light rainfall from reaching the soil surface. Using old carpet for large areas to smother weeds results in the ground being perfect the following year to plant into as the worms have done all the work turning weeds into soil. Layers of newspaper covered with a heavy mulch are also effective but again if you live in a bushfire prone area you will need to use a different method.

In the vegetable garden use companion planting to fill spare spaces with flowers and herbs with foliage that smothers weeds. This also has the advantage of attracting bees.

In order to safely eat your weeds, you need to be very sure that the weeds you are picking are what you think they are. To learn what is edible and what’s not, you need to do your research. Some parts of a plant may be poisonous while others are not.

Chickweed is a little, delicate, herbaceous winter green, also rich in vitamins A, B and C, and a good source of Omega 6 fatty acid and can be cooked like spinach or used as a salad green.

The fronds and stalks of wild fennel can be cooked and eaten in the same way as the store-bought variety and have a similar taste. While Blackberry is a weed of national significance and a real pest for farmers and local councils, its fruit is delicious and can be found in abundance in late summer and early autumn. More information can be found in The Weed Forager’s Handbook by Grubb & Raser-Rowland, Hyland House Publishing.

Integrated weed management

Integrated weed management uses a range of the above control measures.

Future planning and ongoing maintenance

Follow up is essential until the weed’s seed bank is exhausted (an average of 7 years). For some species, such as gorse, this may even be in excess of 25 years.

NRM recommends planning your weed removal as gradual removal ensures native habitat is not lost, new bare areas are not created for more weeds to colonise and erosion is not caused. Remove isolated weeds in areas of good bush and agricultural land first, rather than tackling a dense infestation. Gradual removal allows native species to adapt to the changes, rather than being forced to move. To minimise disturbance plan weed removal and revegetation simultaneously, replanting with desired species such as natives from local genetic stock.

References

Weeds on small farms

http://farmstyle.com.au/news/weeds-small-farms

Identifying weeds

 http://www.environment.gov.au/biodiversity/invasive/weeds/identification/index.html

 www.weeds.org.au/noxious.htm

The Australian National Botanic Gardens

http://www.anbg.gov.au/gardens/index.html

Australia’s Virtual Herbarium

http://avh.chah.org.au/

http://www.weeds.asn.au/about-us/biological-control/

http://www.cpbr.gov.au/cpbr/index.html

Weeds of Australia identification tool

Council of Australasian Weed Societies (CAWS)

http://caws.org.au/index.php

Books:

Tasmanian Weed Handbook by Bryan H. Hyde-Wyatt and Dennis I. Morris

The Weed Forager’s Handbook: A Guide to Edible and Medicinal Weeds in Australia by Adam Grubb and Annie Raser-Rowland (foreword by Costa Georgiadis)

Biological Control of Weeds in Australia by Mic Julien, Rachel McFadyen and Jim Cullen