A weed is any plant that is growing where you don't want it.
A weed will compete with your desired plants for light, space, water and nutrients.
A plant could also be a weed because of a particular characteristic; it could be poisonous to stock or humans, if it acts as a host plant to pests and diseases (of both other plants and/or animals), if it has damaging roots, or if it causes allergies.
Any plant has the potential to be a weed.
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There are many different ways of controlling weeds, and literally thousands of different weed species which might need controlling. It is always important to use the appropriate treatment for the weed(s) in question. Young weeds are far easier to control than older ones. Some chemicals, for instance will effectively kill certain weeds when they are in the early stages of growth, but will not control other types of weeds. You may need to be able to distinguish between types of weeds to determine whether the chemical will or won't work.
STEPS IN CONTROLLING WEEDS
Know what weed or weeds you are dealing with.
Know how those varieties grow, and what conditions they do and don't tolerate.
Then create conditions which they don't like....
You need to consider whether you want to kill or just control the weeds.
When you know these things you can consider which method is best for your situation.
WAYS TO CONTROL WEEDS
1. Suffocation
A popular weed control method is to suffocate the weed (block out light) &/or put a physical barrier over it which it can't grow through. This is more commonly known as mulching. Mulching kills weeds by simply smothering them. The weeds are deprived of light and in order for them to grow, they have to break through the barrier formed by the mulch. A mulch can take the form of almost anything, but the more popular ones in use are:
Wood shavings and chips -Pine Bark, Ecomulch.
Hay or Straw. -Grass Clippings.
Leaves. -Newspaper.
Carpet underfelt -Cardboard
Seaweed -Woodchips, sawdust, leaves etc.
The depth of the mulch will be determined by the weeds that you are trying to control. Vigorous weeds will need a greater depth of mulch than perhaps small annual weeds. Most weeds seedlings will require a depth of mulch of 8-10 centimetres over the top of them.
Mulch Mats - these are also known as weed mats. They are usually made of a closely woven fabric, that have holes large enough to allow water to penetrate through, but they are small enough to prevent most weeds from growing through.
Some trees & plants with dense foliage or foliage right to the ground will shade out weeds. Such trees include: Ash, Maple, Citrus, Salix, Casuarina, Pines.
Shrubs which shade out weeds include Diosma, Grevillea, Conifers, Coprosma repens, Echium fastuosum.
Other plants and trees drop lots of leaves, which create their own mulch. Examples of these are:-
Conifers-pine needles deter weed growth
Eucalypts -oils in leaves deter weed growth
Melaleucas and Leptospermums -oils in leaves deter weed growth
Acacias -tannins are washed off the leaves by rain in some species.
A border of weed suppressing plants can be grown around a vegetable patch to prevent entry of spreading weeds, such as couch and kikuyu grass. Comfrey or lemon grass may be used for this.
2. Burning Weeds can be burnt with a flame, or with heat created by covering temporarily the weed with a plastic sheet (this is known as solarisation).
Fire -Weeds can be burnt either using a flame thrower (if weeds are green or dry), or by lighting a "controlled" fire (if vegetation is dry enough to burn). When burning the weeds it is essential to follow fire prevention regulations for your area. Contact the local fire brigade for details. Burning will always leave a residue of charcoal, which is dirty, but will disappear with time. Flame throwers are portable burners fuelled by Paraffin or Propane Gas. They can usually be hired from a hire shop for a reasonable price. Care should be taken with them as the heat generated from them can be quite considerable, and can also damage other plants, as well as causing nasty burns to the operator. Flame throwers are useful along fence lines, roadways or paths, or any other area where the flame won't cause unwanted damage. Burning off can be an excellent method of controlling large areas of weed growth, on vacant or rural land, or to control large clumps of problem weeds such as blackberry. It can be dangerous though if not done properly and under the right weather conditions. Never use fire on windy or very hot days. Never burn more than you can control easily with manpower and water available. Mow fire breaks before commencing a large burn to confine the operation to a series of small burns. Wear full clothing (eg. firm boots, overalls and a hat); and have a first aid kit on hand. Above all, check with the local fire brigade before burning.
Plastic Sheet -This method is also known as solarisation. Large sheets of clear plastic are spread over the surface of the ground in warm weather. The sun's rays will cause the ground under the plastic to heat up enough to kill many types of weeds and soil diseases. After a week or so the plastic can be removed and the area planted. Solarisation is an ideal method of ground clearing prior to planting a vegetable garden, or annuals in a border, and is relatively cheap.
3. Cultivation.
Cultivation, or the digging of the soil with either a spade or a hoe, will often kill weeds, especially annual weeds. Weeds can be controlled by physically burying them in the soil, and regular hoeing of the soil surface may deter some types of weed seeds from germinating. Weeds that do germinate will be easily chopped off with a hoe. Regular hoeing of the soil surface will also assist in water penetration of the soil.
In some cases where weeds have a vigorous root system, cultivation alone may not be enough, and the weeds may well have to be physically removed by hand. It is advisable not to water the soil directly after cultivating, as hot sunlight can kill exposed weed roots. Some weeds are almost impossible to control by hand, for example, couch, kikuyu and wandering jew, or weeds with bulbs or corms (e.g. oxalis, watsonia).
In some cases cultivating can worsen a weed problem by chopping up and spreading underground parts such as roots, rhizomes or bulbs. Many weeds are adapted to invade cultivated or otherwise disturbed ground. Some weed seeds require light to germinate, and cultivation can bring these to the surface so mulching may be required as well.
Soil which is cultivated often is easier to cultivate so don't put the job off.
Young weeds are damaged more by cultivation than established weeds
Do not water after cultivation. (The hot sun kills exposed roots).
Some weeds will die quickly when you cut the top from the roots (others will regrow from the smallest piece of stem or root lying in the soil)
There will always be some hard to kill weeds which need removing by hand.
Moist (but not wet) soil is easier to cultivate. Wet soils should not be cultivated, however, as this destroys soil structure.
4. Grazing.
One of the best animals to effect weed control by grazing would without doubt have to be the goat. They will eat virtually anything, including ropes that act as a tether for them. They also have a great deal of strength and will easily break down weak barriers that are designed to keep them in. With this in mind then it is important to only allow the goat access to the weeds and not the desired plants. In a small back garden it may be difficult to keep the goat under control, but in a large area this will not be so much of a problem. Probably the ideal use for a goat would be in cleaning up an area, before you make a new garden there.
Here are a few hints if you're considering a goat:
You're better to borrow one than buy one. Otherwise when you run out of weeds, feeding it can become a problem.
Goats are best used to keep a wild area under control on a large property, or to clean up an area prior to making a new garden there.
Goats are very strong. They can break small gauge chains, eat through ropes and pull stakes out of the ground. Use a heavy chain and tie them up to something very solid such as a fence post or large tree.
Goats will stand on their back legs to reach plants, they will eat all types of plants and even strip the bark off trees.
The goat makes a tempting target for roaming dogs, unless it is well protected (good fencing).
Sheep can also be used for grazing, but can be a little more choosey in what they are prepared to eat. Chickens, ducks and geese will also eat a variety of weeds, and cultivate the soil by scratching. Wire netting is sometimes placed on the ground in a poultry run to stop hens digging up the soil too much. Penned pigs will also cultivate the soil with their digging. Even pet rabbits, or guinea pigs can be caged and allowed to graze weeds.
5. Mowing/Slashing
This involves cutting the tops off the weeds on a regular basis, ideally before any seed heads develop. Any cut foliage should be allowed to fall back on the beds and this will help to return nutrients to the soil. If the weeds are long in growth when cut, then they may well act as a mulch, preventing other weeds from germinating and growing. The weeds should be cut close to the ground to effectively control them, and an ideal machine to use would be a brushcutter or whipper snipper.
6. Flooding.
Flooding of an area will kill a wide range of weeds but not all. This method is sometimes used on flat sites prior to planting.
7. Changing pH
By raising soil pH you can discourage growth of some weeds, such as Sorrel (Rumex sp.). Adding organic matter to the soil will also gradually cause sorrel growth to slow down.
8. Biological Control
This involves introducing natural predators into an area to attack weeds.
It is a method which has been used occasionally with dramatic results, but which can "backfire" if the full implications of introducing something new into an environment are not understood.
Prickly Pear
Prickly Pear (a cacti which was a severe problem in the past) was brought under control in Australia by introducing a parasitic moth which has a grub that attacks the plant.
Blackberries
A rust (fungal) disease was introduced into Australia in the 1980's in an attempt to control blackberry weeds. Though this has had some affect, to this stage it has only been a mild deterrent.
Water Hyacinth
Insects have been used to control the spread of water hyacinth in the United States and Australia.
9. Chemicals
There are a wide variety of herbicides used to control weeds. The majority of these are used for agricultural purposes, or by larger industrial concerns, or government departments (local, state, etc.), or service agencies (e.g. water, power, sewerage authorities). The range of herbicides available for the home gardener is relatively limited by comparison. Some of the more commonly used herbicides are: Glyphosate (Round Up, Zero), Garlon, 2,4-D, Dicamba and MCPA. These are discussed in greater detail in chapter 2.
IDENTIFYING WEEDS
As adult plants, weeds are much easier to distinguish from one another. The plants become different in size and shape, the leaf colours vary and the flowers which appear also vary.
However young weed plants are all the same size, frequently have similar coloured foliage and don't have any flowers to help you distinguish them one from another. When weed seedlings appear in a young crop (eg: vegetables), it can be difficult to tell the crop from the weeds.
TYPES OF WEED PROBLEMS:
Weed problems occur in many different situations; and the appropriate treatment will be different in each situation.
FENCELINES AND BORDERS
These are weeds growing alongside a fence or house wall, on the edge of a path, garden bed, or at the base of some other structure (eg. seat, gazebo, or statue).
Weed control here is simple with residual weedicides such as "once a year path weeder" or kerosene spot sprays. These chemicals kill the weeds and deter new weed growth for months.
Weeds in these areas may also be cut regularly with shears or a brushcutter, but this may need attention weekly to maintain appearances. Alternatively the area beside a wall or around a garden feature can be surfaced with mulch, gravel, or even paving to deter weed growth.
WEEDS AT THE BASE OF TREES
Trees in lawns or home orchards often develop weed growth too close to the trunk to be reached by normal mowing. A brushcutter can be used in such situations, or if you want to minimise work, it may be preferable to use an organic mulch such as wood chips or bark around the tree trunk, then spray a few times each year if necessary with roundup or zero (only when weed growth appears).
WEEDS IN GARDEN BEDS
The best way to control weeds in garden beds is to kill all weeds before you first plant the bed, then avoid bringing any new weeds into the garden. Only use clean weed free soil from reputable garden product companies, even if it costs more. Never bring plants into the garden which have weeds growing in the pots. Even if you pull the weed out, some root or seed may remain to grow into a new weed. Flower or vegetable gardens which need periodical replanting will inevitably still grow some weeds. Some hand weeding will always be necessary in these situations, particularly when seedlings are young and small. Shrubberies can be mulched to minimise the need for hand weeding.
Sometimes persistent weeds can take over areas though, and no amount of hand weeding is likely to remove the problem. It is sometimes better to face facts and sacrifice an area of garden. In such areas, first remove everything you can by digging over with a fork, then spray regrowth a 2-4 weeks later with roundup or zero. Finally cover the area with a clear plastic sheet for up to 1 week to "cook" any remaining weed tissue or seed. After removing the sheet, the area can then be redeveloped.
WEEDS IN HARD SURFACED AREAS:
Weeds often grow between pavers, in gravel driveways or even in cracks in concrete. Kerosene spot sprays or milder chemicals such as zero will kill most weeds in these areas, but may not stop new weeds springing up a few weeks later. Hand weeding often does not work, because it is difficult to remove all of the roots, and if you pull the top off a weed, the roots will probably just regrow.
Residual chemicals such as "once a year path weeder" are often more useful, remaining in the ground for several months killing not only existing weeds, but new ones as they germinate.
PLANTS THAT GO TO SEED (e.g. pyrethrum, forget-me-not, lemon balm)
Many of these plants set prolific amounts of seed during the growing season which mature and fall to the ground. These seeds may well germinate during the growing season, or will germinate in the spring. Whatever the time the seeds decide to germinate, there will be a great deal of them, and you can be faced with a mass off new and unwanted seedlings. These weeds must be eradicated before they ever drop seed, so act immediately as soon as you see a flower!
VIGOROUS, INVASIVE CREEPERS that take root (periwinkle, ivy)
These type of plants readily spread across shrub borders with long, branching shoots. These will tend to wind themselves around the other plants and will also readily root into the ground if they come into contact with it. This means that the plant is able to spread very rapidly. Once these roots have become established, it can become difficult to control the plants growth. One spray of chemical is rarely enough for such weeds. The only sure way is often to dig the plants out then spray the regrowth several times before replanting.
SUCKERS
These plants which spread by suckers or underground roots (eg. raspberry, willow, bamboo, couch grass, kikuyu). One of the main features with this type of plant is that you do not know about the problem until it appears. As the plant is spreading underground, the roots can travel some distance before they surface. Just cutting the growth off where it appears will not solve the problem, as the roots may will reshoot from the buried root. The only sure method of control is to dig the root or sucker up along it's total length, cover with a heavy mulch and spray any regrowth repeatedly.
UNDERGROUND RHIZOMES,TUBERS, BULBILS AND CORMS (Onion Grass - corms, Soursob - tubers and bulbs). Many weeds reproduce not only by seed but also underground by stolons, suckers, bulbs corms or by small pieces of stem or root.You cannot merely pull these weeds out as the underground bulbils or a root section are invariably left in the ground to reproduce.
A combination of hand and chemical control may be necessary.
WEEDS IN LAWNS
Weeds normally occur in lawns when one or several of the following happen:
Environmental Stress such as poorly drained or watered lawns; sun burn, and cold damage
Damage by Pests. Insects damage the turf plant's roots weakening it and allowing weeds to compete easier with the turf.
Poor Cultural Practice - Close mowing lowers the level of health in the turf, or creates bare patches of soil, where weed seeds can germinate.
Heavy wear from vehicles or foot traffic damaging turf grass, causing soil compaction etc. Anything which reduces the general health and vigour of turf plants will make it easier for stronger growing weed plants to invade the turf.
There are weedicides which will kill broad-leaved weeds in lawns without affecting grass but these also kill clover, and for lawns which contain a lot of clover, this may be undesirable. Other weedicides such as zero can be used to spot spray particularly badly affected areas. This may kill grass as well as weeds, but it will leave you with a clean surface which can then be replanted with whatever you prefer. For a "perfect lawn" some hand weeding will almost always be essential.
POISONOUS PLANTS
There are both weeds and common garden plants which are poisonous. Poisonous plants are considered to be weeds (ie. unwanted plants) by many people, though others may in fact prize those plants for their beauty. Some poisonous plants cause mild irritation such as skin rashes, but others can cause serious illness or even death.
Common poisonous plants include Arum Lily, Datura or Brumgansia (Angels Trumpet), Dieffenbachia, Digitalis (Foxglove), Nerium (Oleander) and Rhus.
NOXIOUS WEEDS
These are weeds which have become such a serious problem that they have been declared "noxious" by government authorities. Once a weed is declared noxious, it becomes illegal to grow that plant either intentionally or unintentionally. Property owners may be forced to eradicate the weed or have government authorities enter their property and eradicate it. Fines may be incurred for growing the plant. Weeds may be declared noxious in one part of a country and not another, or may be considered noxious throughout an entire country.
ENVIRONMENTAL WEEDS
Many garden plants escape into bushland areas, where they can compete or even completely take over from the native vegetation. Foreign plants will flourish without the pests and diseases that kept them in check in their original country, if suitable pollinators and seed dispersing animals are present. All at the expense of the native plants. A European broom for example, could replace a native wattle. Plants may spread by being dumped (common along railway lines) or by seed, often carried by birds. Another problem is that garden plants can sometimes cross pollinate with the local native (called indigenous) plants, for example Grevillea species and cultivars. This interbreeding results in hybrids which interfere with the natural evolution of the indigenous plants.
In the middle of suburbia, growing these types of plants is not a great problem, but if your garden is near an area of native bush, there is a strong chance of garden plants escaping. Many road and rail reserves, foreshores and national parks are now infested with environmental weeds. The situation can be so bad that all weed control methods may be needed - including hand, chemical and biological control. The loss of natural Australian bushland is a great cost to the community, in lost educational and recreational opportunities, the loss of indigenous plants and animals, as well as the public funds used (or not used) to control the problem.
As an individual you can approach your council or shire and see if there is a community group involved in treeplanting, revegetation and weed control. Speak to the staff at your local nursery and see if they will put up a list of problem plants in the nursery and suggest alternatives. There may also be a nursery near you which grows local plants.... support them and grow some in your own garden. It is also worthwhile talking to your neighbours and encouraging them to compost their garden wastes rather than dumping them into bushland areas.
COMMON WEEDS
There hundreds if not thousands of different weeds. Some of the more common types of weeds are outlined below.
Bamboo (Bambusa spp)
There are many different species of bamboo, most having the potential to become a serious weed. Underground rhizomes can grow under lawns, buildings or even concrete and sprout leaves on the other side of a garden. Spraying with zero (or roundup) is effective on small, contained plants. Large networks of roots are best removed by hand as far as possible then left for regrowth to develop which is then spot sprayed repeatedly with either glyphosate or kerosene.
Bindii (Soliva pterosperma)
A serious lawn weed particularly in warm climates. This fine leaved ground hugging plant produces sharp burrs which can be painful to bare feet. Yates Bindii Weedkiller will effectively control bindii without damaging grass in a lawn.
Blackberry (Rubus fruticosus)
A vigorous prickly and deciduous clump forming plant. Leaves are green on the upper surface and silver green underneath. Berries are edible and loved by birds which spread the plants by spreading the seed. One spray rarely kills blackberries though glyphosate will affect it and various "tree and blackberry weedicides, such as Garlon, are relatively effective.
For the best control of severe infestations, slash, burn, cultivate then spray regrowth repeatedly.
Bracken Fern (Pteridium esculentum)
This is a vigorous spreading fern which occurs widely throughout the world. It is difficult to kill in any situation. Mowing infected areas of lawn will deter growth, but still take up to 5 years or more to remove the weed. Bracken is poisonous to some animals so grazing is not usually recommended. The chemical Metasulfuron is perhaps the best chemical treatment, but even this will often give unsatisfactory results. Repeated spraying of roundup may also deter growth.
The most satisfactory control involves a combination of methods: digging out by hand, slashing, burning and repeated spraying.
Capeweed (Arctotheca calendula)
A low growing annual with yellow black centred daisy flowers. It is a common problem in lawns and pasture land. Lobed leaves have fine hairs. Plants spread hugging the ground shading grass in lawns and leaving bare patches when they die. Small numbers of plants are best hand weeded. Spraying with 2,4-D, MCPA or Dicamba based weedicides can be effective, particularly on very young plants.
Clover (Trifolium spp.)
These spreading legumes actually help improve the soil, and as such some people actually like them in a lawn. Clover is most commonly a lawn problem, where people desire a high quality lawn with the even texture of grass. Treatment with hormone weedicides such as Yates Bindii Weed killer or Weed 'n Feed will remove clover without affecting grass. If the plants are large, several applications will be needed. Clover in garden beds is best removed by hand weeding.
Dandelion (Taraxacum officinale)
Dandelions have a deep thick main root below a low rosette of indented dark green, hairless leaves. Flower stems rise from the centre of the rosette to produce bright yellow daisy like flowers. Dandelions can be a problem in lawns, garden beds or even paths and paving. Control is the same as with cape weed. In paths or other places away from garden plants they can be controlled with zero, kerosene or once a year path weeder.
Hand weeding is only effective if the root is properly removed.
Dock (Rumex spp)
These annual plants have large, usually lance shaped leaves. Masses of small flowers develop on tall upright stems developing into a large plume like brown to rusty seed head. Dock grows most commonly on poorly drained or waterlogged soils. Mowing and draining an area will deter the weed. Small quantities can be removed by hand provided the roots are also removed. Spraying is effective with dicamba or zero.
Gorse (Ulex europeus)
A very prickly evergreen shrub, to 4 metres tall, with yellow pea flowers. A noxious weed in Tasmania and serious problem in some other areas. Control by pulling out by the roots, burning or grazing. Alternatively, spray glyphosate (ie. Zero or Roundup); but be prepared to spray regrowth several times in severe infestations.
Grasses
There are many different types of grasses which may become weeds. Grasses are either tussock (ie. clump) forming plants or creepers. Creeping grasses sprout roots along their creeping stems; a desirable habit in a lawn, but one which multiplies it's weed potential elsewhere. Grass seed is generally light, blows around the garden easily and sprouts readily. Young grass plants are controlled by cultivation or hand weeding. In paths, fence lines or if otherwise isolated from garden plants, burning or spot spraying (with glyphosate or kerosene) is very effective. Mulching is also useful to minimise grass weeds.
Lantana (Lantana camara)
This woody, spreading shrub is grown as an ornamental plant in cooler climates, but is a serious weed in warm areas. Flowers can be white, red, yellow or pink. Foliage can be prickly. Note; there are other types of lantana which are not weeds!
Control is similar to blackberry control. Large clumps may be burnt or dug out. Spraying glyphosate, kerosene or a blackberry killers, such as Garlon, is often effective, but regrowth may require spraying repeatedly.
Nettle (Urtica urens)
Commonly called Stinging Nettle, this small prickly weed gives a sting when touched which becomes an irritating itch. The juices of the same plant are an antidote; so if affected, immediately squash the plant and rub it into the itchy area. Glyphosate (ie. Zero) will readily kill nettles.
Oxalis (Oxalis spp.)
There are a number of different species of oxalis, some being grown as garden plants but many being serious weeds. They all have clover like leaves, attractive colourful flowers and grow from small bulbs. They are difficult to eradicate as a weed because the bulbs produce many small bulblets each year which break away very easily when the soil is disturbed. Hand weeding or cultivation inevitably leaves many small bulblets in the soil which will eventually grow into new weeds. Repeated spraying may reduce an oxalis problem. Mulching is often ineffective as the bulbs can emerge through the mulch from a great depth. Sterilising the soil with solarisation may be effective if all of the bulbs are close to the surface. Some experts claim that the only way to completely eradicate oxalis is to remove "all" of the soil which it inhabits!
Singapore Daisy (Wedelia trilobata)
A vigorous self layering creeper with rich green leaves and yellow daisy flowers. Though grown as a ground cover in many home gardens, it is very vigorous and difficult to eradicate once established. Many gardeners in Queensland consider it a serious weed. Roundup, zero or kerosene sprays will affect it, but usually it will regrow from the smallest piece of stem or root. The most effective control involves digging out followed by repeat spraying then heavy mulching.
Thistles (Sonchus, Cynara etc)
These are prickly herbaceous plants which with colourful (usually bluish or yellowish flowers). Some are small annuals while others can live several years and grow to 1.5 metres or taller. Remove flowers before seed develops as plants multiply very readily from seed. Spray with MCPA or Dicamba.
FOR MORE DETAILS ON OUR WEED CONTROL COURSE click here
Suggested Reading
Weeds -an ebook by John Mason -click for details