AVON VALLEY WEEDS

The information in this document has been compiled by Terry Piper, former Department of Agriculture and Food weed scientist, to assist landholders, landcare groups and others based in the Avon Valley to better understand and manage weeds.

The weed species

Annual species

The symbol of the valley. Its purple flowers impress the tourists, but it contains pyrrolizidine alkaloids that are toxic to grazing animals, especially horses and pigs. Sheep and cattle are more tolerant as the alkaloids are broken down in the rumen. Sheep in fact keep the weed in check to a certain extent, but will not thrive if they have nothing else to eat.

Introduced from the Mediterranean as a garden plant, its seeds may remain dormant and viable for 4-5 years at least. It has no particular temperature requirements and so may appear at any time of the year.

Readily controlled with B group herbicides, but has become resistant to these in the Perth hills area. If controlling this way, ensure that any survivors are controlled mechanically when they flower.

Being an upright plant, it can also be controlled by wiping with glyphosate, metsulfuron or chlorsulfuron.

Can be well controlled by mowing, as it is highly visible at flowering. Also vulnerable to cultivation and solarisation.

Capeweed (Arctotheca calendula)

From the daisy family (Asteraceae), its seeds are covered with a fluffy "wool", and will spread with the wind over long distances.

Can be controlled with a range of herbicides in clover pasture, but the products available will all reduce the clover growth to some extent.

It is also vulnerable to mowing, but this must be close to the ground.

Doublegee (three cornered jack, spiny emex) (Emex australis)

Another plant that has no particular temperature requirements and so may appear at any time of the year.

It is a nuisance in crops, but can be readily controlled. It provides early grazing in pastures, but the achenes begin to form very early and from then on the animals avoid the plant. If the pasture is not overgrazed, other plants such as clover and capeweed will out compete it, but under hard grazing these will be removed leaving the doublegee a free run.

Can be controlled by herbicides in clover pastures, but its growth habit is too prostrate to be mown.

Its seeds will remain viable for up to 15 years, so eradication is a long term process. If you have a bad infestation consider turning the area into a grass pasture for several years. The doublegee can then be controlled by a range of herbicides until its seed numbers decline to negligible levels. If you ever have to crawl across a paddock with a broken leg, you will be glad these fellows are not there. The author can vouch for this!

Corkscrews, wild geranium, shiny leaf or long storksbill (Erodium botrys), ferny leaf or musky storksbill (E. moschatum).

Of Mediterranean origin, the plants are related to the garden geraniums (that are mostly Pelargonium species). The genus is easily recognised by its characteristic seeds with their twisted "corkscrew" awns. E. botrys has more deeply divided leaves.

The seeds can be a physical hazard to stock, sticking into wool and fur and then penetrating skin. The plants have very little value as forage, and can be weeds in crops. Can be controlled by cultivation, by glyphosate, metsulfuron or chlorsulfuron. Solarisation should also work, as could mowing at flowering, although these plants are often low growing.

This is one dicotyledonous species that is susceptible to grass selective herbicides, especially haloxyfop. This could be used by those wanting control in clover/medic pastures.

Flatweed, catsear (Hypochaeris glabra, H radicata)

The tall flowers are susceptible to mowing and grazing. It is also readily controlled in lawns by any of the specialty lawn herbicides containing MCPA and bromoxynil. Caltrop (Tribulus terrestrilus).

An obligate summer grower in this area, so it will only appear after summer rains. In some years it is really bad, in others it will not be seen. There are also several similar native species, but these generally have less spiny fruits. See the comments about doublegee fruits above - caltrop has fruits that are possibly more unpleasant. Eradication is essential, and vigilance against introduction is critical.

Readily controlled by herbicides in most situations, as few other pasture plants are alive at the same time, and selective control is easy in lawns and grass pasture. It generally grows too low to mow, but could be controlled by solarising.

It is definitely a plant against which an eradication campaign is worth mounting. Incidentally, the original caltrop was a weapon of war - an iron device with four tetrahedral prongs that was strewn in the path of enemy horses. However it fell, one prong was always upright, ready to lame the horse. Charming - but walk on the plant with bare feet and you will agree that it has been well named!

Stinkwort (Dittrichia graveolens)

It is also from the Asteraceae family, and has fluffy seeds that are readily wind spread. It is not susceptible to many herbicides, the oily leaves reducing uptake of most chemicals. It can be controlled by 2,4-D ester, but this product must be used with caution as it is liable to cause off-target damage. It cannot be used in restricted spraying areas.

Being an upright plant, it is easily controlled by mowing and this should be the method of choice for dense infestations. Isolated plants are easily controlled by hand weeding or hoeing. As a summer grower, its potential to recover is usually limited by low soil moisture levels. Thus in most years a maximum of two mowings would be needed.

Wild oats (Avena fatua, A. barbata)

Wild oats are not always regarded as a weed. They can provide useful early grazing, although fodder quality declines as they mature. They are very competitive in crops, and they become a fire hazard when they dry off.

Can be controlled in crops and native vegetation by selective herbicides. In pastures they can be controlled by mowing and/or hard grazing. Cultivation is effective, but usually stimulates more seeds to germinate. Seedlings can also be solarised. Avena species originated from the lands of the eastern Mediterranean, where they probably contributed to early human civilisation.

Ryegrass, annual or Wimmera ryegrass (Lolium rigidum)

Ryegrass is a serious weed of cropping. Selective herbicides are available for its control, but ryegrass has shown a remarkable ability to become resistant to a wide range of herbicides. As a result Western Australia has the dubious honour of being the herbicide resistance capital of the world!

Whether you choose to have ryegrass on your property is an individual decision, balancing its value in a pasture against its potential for ARGT and its weediness in crops. It can be well controlled by grazing or mowing at seed set. Selective herbicides in autumn will take it out of legume pasture, but remember its resistance potential and clean up any survivors at seed set time.

Farmers spray the developing seed heads with paraquat to kill the seeds, but this product is too toxic to be recommended to smallholders. Glyphosate can achieve a similar result, but will affect clover seed set as well.

Ryegrass has little seed dormancy, and 2-3 years of effective control will come close to eradication.

Other grasses (brome grass - Bromus spp., barley grass Hordeum spp., silver grass Vulpia spp. etc)

Slashing as seed heads form will reduce this problem in the immediate year. Regrowth invariably occurs, and several slashings will be needed for full control. Such a program will eventually come close to eradicating these species.

Alternatively, the pasture could be sprayed in early winter with a grass selective herbicide. This will remove Bromus and Hordeum (and ryegrass and wild oats) and leave a clover dominant pasture. If such a program is undertaken, ensure there is enough clover component in the pasture or else the pasture will provide little feed value.

Vulpia species are not affected by the usual grass selectives, but simazine at 500 ml/ha provides selective control.

As with ryegrass, these grasses have little seed dormancy, and they can also be decimated with 2-3 years of good control.

Perennial species

Arum lily (Zantedeschia aethiopica)

Cultivation will break up large clumps, but will also spread the plant as it regrows from root fragments. Regular slashing will probably be effective.

These are among the few plants against which glyphosate is not very effective. Spot spraying will work to some extent, as the effective rate applied is 10+ l/ha, but this rate is uneconomic for boom spraying.

By far the best control is spraying with chlorsulfuron or metsulfuron at flowering. Blanket wiping could also work for clumps that are small enough for the wiper to cross. Cape tulip (one leaf Homeria flaccida, two leaf H. miniata).

Another valley symbol, and even more toxic than Paterson's curse. Educated stock seem to avoid it, but losses have occurred. The dry material remains toxic, and is probably more palatable than the green material. During summer, when feed is in short supply, stock are most at risk.

Both are from southern Africa, and were introduced as garden plants. One-leaf tulip tends to have more seed pods, while the two leaf species has bulbils in its leaf axis. Both produce cormils around the underground parent corm.

They are both perennials, regenerating each year from the corm. Thus they cannot easily be eradicated by slashing or solarising. The top growth is removed but the corm is untouched. Slashing may work IF it is done very regularly. As soon as the plant produces new leaves, they must be cut off, before they can photosynthesise and renourish the bulb. By far the best control is spraying with chlorsulfuron or metsulfuron. The plants are also very suitable for wiping, especially in grazed pastures where the surrounding vegetation has been eaten down.

Another plant against which glyphosate is not very effective. Again spot spraying will work.

Oxalis species (sour-sob - Oxalis pes-caprae, purple wood sorrel or four o'clock O. purpurea, finger leaf oxalis O. glabra)

Galahs however are avid consumers of O. purpurea bulbs. Flocks will settle on the ground and spend hours digging up and eating them.

They regenerate each year from bulbous root systems, which allows them to get away quickly after autumn rains. They do need cooler weather, so don't appear in great numbers after summer rain.

Soursob can reduce crop yields by up to 80%, and all species will come to dominate pastures as grazing animals tend to avoid them.

To be effective, cultivation needs to be deep and thorough and probably will need to be repeated. Mowing is generally not practical given the relatively short growth habits. Soursob especially also grows around the base of trees where it is not accessible to motorised mowing.

The best control is achieved by herbicides, either glyphosate or chlorsulfuron.

Guildford grass (onion grass Romulea rosea)

Can be eradicated from lawns by frequent mowing with a rotary mower. The stems must be slashed off as soon as they regrow, before photosynthates can replenish the energy the bulb has used to produce the leaves. Eventually the bulb will be exhausted of reserves and die.

Close slashing like this is not practical in most paddocks, but cultivation will give some degree of control.

Pigs will root out and eat the bulbs.

The best control in paddocks is by chlorsulfuron or metsulfuron. Good control has also been achieved with blanket wiping, but the Guildford grass needs to be very vigorous and high and the other pasture grazed down fairly hard.

Dock (Rumex spp. Curled dock (R. crispus) is perhaps the most common)

Controlled in paddocks by cultivation. The flowering stems can be slashed off to reduce seed set, but this will need to be repeated several times each year, and will have no other effect on the plant. It will still be there next year.

Individual plants can be spot sprayed with glyphosate, while dense infestations are best treated with chlorsulfuron, metsulfuron or dicamba.

Watsonia (5-6 species Watsonia bulbulifera is most common)

It could probably be controlled by intense, repetitive slashing but it tends to grow in situations that machines cannot access. Thus most slashing would need to be by hand-held brush cutters.

Isolated plants can be hand pulled, but make sure that all corms are lifted from the soil and left where they cannot take root again.

Spot spraying with glyphosate will control the plants, even if some of the "spots" are many metres in diameter. Chlorsulfuron and metsulfuron also provide control. In accessible areas, blanket wiping has been quite successful.

Afghan thistle (Solanum hoplopetalum)

One of the prickliest plants around, it is a prostrate summer grower that dies back during winter. Prominent on roadsides where it is spread by grading, it also takes over grazed paddocks as it is avoided by stock.

The roots fragment easily and then produce new plants, so cultivation actually makes any situation worse. Small infestation might be controlled by repeatedly chipping off the top growth, or by solarisation.

It can be controlled best by Tordon. This cannot be used in restricted spraying areas, where a very high rate of glyphosate is probably the only option. Control will only be feasible in years of summer rains, as the plant must freshen up and produce leaves that can absorb enough herbicide to kill the root system.

Couch grass (Cynodon dactylon)

Cultivation tends to spread the plant rather than controlling it, and mowing turns it into a lawn! Solarising will give some control, but will require extra watering in most summers.

Glyphosate or grass selective herbicides are the control methods of choice. Again, control should only be attempted in wet summers when the plant has plenty of leaf area. It should not be grazed beforehand, and extra fertiliser will assist with growth.

African love grass (Eragrostis curvula)

Individual tufts can be controlled by spot spraying with glyphosate or a grass selective. Old stands may first need a spring burn to remove dead material. Then spray the fresh regrowth when a substantial amount has appeared. Control will be best in wet summers which encourage growth.

Control measures

Some basic principles

Plants have evolved many different methods to spread into new habitats. Some use the slow and steady technique of spreading root systems, such as couch and kikuyu grasses. Others use the wind to spread their seeds far and wide in one fell swoop, such as flatweed and capeweed.

Still others enlist the aid (usually unwitting) of animal vectors. Corkscrews, doublegees and many grasses do this. Their seeds are adapted to stick to animals skins and hooves and to thus be carried about. There is little a landholder can do to protect against windborne seeds, but good farm hygiene can prevent the introduction of many other weeds. If you are buying in hay, ask the supplier to state its potential weed seed content.

While such a statement should not be relied upon blindly, a reputable supplier should be honest about possible contamination. The best guarantee is to know the weed status of the paddock where the hay was cut. It makes sense to always feed out hay in the same small area. Any weeds introduced will then be in that area rather than spread over the whole property.

When purchasing new stock, leave them penned for a few days if possible. Any weed seeds in their intestines will then be excreted in that area rather than spread. Some seeds will even survive passage through a ruminant, although horses are worse in this regard. Buying newly shorn sheep rather than those in full wool will also reduce the risk of introducing weeds.

Be especially careful with car tyres and your own clothing. Tyres and shoe soles will collect doublegee and caltrop seeds and transport them long distances. Trouser cuffs collect all manner of seeds, while corkscrews and grass seeds are attracted to socks. Inter plant competition.

Plants require water, light, and nutrients to grow. In any given area of land there is a finite amount of these, and in most situations there is not enough of any of them for all the plants to grow to their maximum possible size. If any plant is weakened in some way, it will be outgrown by the others, starved of its growth requirements, and die. Thus one of the best ways to control weeds is to provide other plants to compete against them. A good healthy oat crop will outgrow and suppress most weeds.

Many herbicides are made to be used in-crop, and the label rates for control of various weeds in those crops assumes some measure of crop competition. If they are to be used to control the weeds growing alone, the rates required will increase.

Pastures that are heavily grazed tend to become full of unpalatable plants, generally regarded as weeds. Sheep and goats especially are selective grazers, and will choose those plants they find nicest to eat. Thus clover and rye grass will be eaten, while doublegee, Paterson's curse, erodium, silver grass etc are avoided. Over time, the pasture will be largely composed of these less favoured species.

Pasture quality

Generally speaking, a mix of species makes the best pasture, rather than a monoculture. Grasses germinate quickly on the opening rains, so a grass of some sort will provide early feed. It helps if the grass remains palatable even after it dries off in summer, so in this regard ryegrass is better than brome or barley grasses. The grass will use the excess nitrogen fixed by the legume component of the pasture.

A legume such as clover should be present to provide extra protein for the grazing animals. Legumes are generally slow growing in autumn/winter, but make rapid spring growth. They also provide better quality dry feed for summer.

Other broadleaf species such as capeweed provide poor pasture, although there are many animals in Western Australia that survive on such a pasture.

Any of the plants noted as being poisonous should be eradicated at all costs. Any plans to replant a pasture should include the removal of such plants. Remember that it may take a year or more to accomplish this.

Any wetter areas os a paddock will remain green longer, perhaps permanently, and will therefore be grazed much harder over the summer period. Such areas will benefit from the presence of a creeping grass such as couch, kikuyu, or paspalum to help bind the soil. Horses are especially bad for cutting up the soil surface and leaving it prone to erosion.

Annuals vs perennials

It is necessary to realise the basic differences between these two classes of plants when planning an eradication program for any weed species.

Annuals die off each year, and rely on the seeds they have produced in the past to continue the species in the following year. Thus a prime aim must be to prevent any of this year's plants from setting seed. The weed may be targeted when it is small, but it can also be targeted at flowering, just before the first of the flowers can mature their seeds. Late control will allow the weed to compete with more desirable species, and the overall production of the land will be reduced, but in the long term the weed's abundance will be reduced.

Such control may be chemical or mechanical.

Most species produce seeds with some degree of dormancy. This means that a percentage (ranging from 95% to 20%) will germinate the next year, but the rest will germinate (at diminishing rates) over the next few years. In some species, a percentage of the seeds will not germinate for up to 15 years, and the control program must continue for at least this length of time. If control is missed for one year, and seeds are set, the whole process must begin anew.

Perennials generally do not set as much seed, as they expect to live for many years. They may die back over summer (watsonia, sour-sob etc) or winter (lovegrass, afghan thistle etc) but they have storage organs such as roots, bulbs, corms etc which remain alive, with reserves of carbohydrate, to regrow as soon as conditions become favourable again. If their seed production is curtailed, as it can be for species such as dock, lovegrass, watsonia etc, any further spread will be prevented, but the parent infestation will remain.

Herbicides

Many people have a philosophical objection to using herbicides, believing them to be artificial and unnatural. Yet properly used, herbicides are an environmentaly friendly method of weed control. They do not cause the loss of soil structure that repeated cultivation will, and in some cases the correct use of selective products allows weeds to be removed while leaving desirable plants unaffected.

On the down side, herbicides must be fully understood if adverse side effects are to be avoided; and herbicide technology is a complex science.

Some products have residual effects, and may cause unwanted plant damage some time after application. Most have the potential to cause damage to off-site plants if they are applied in a way that allows drift to occur.

Herbicides affect only actively growing plants. If they need to enter the target plant by leaf absorption, they must be applied when the target has sufficient leaf area to absorb enough chemical to kill the roots. Thus plants such as love grass and watsonia which die back in winter or summer respectively, must be allowed to regrow to near full size again before being treated. Plants like love grass that tend to retain old material may also need to be burnt or slashed to remove this, so the new growth is more exposed to the spray.

Off target damage Herbicides are very useful if used correctly, but can cause a lot of damage if misused. The main cause of disputes between neighbouring farmers today is crop damage from herbicide drift. Our agriculture is based on rotational cropping, where herbicides used in one phase (say cereals) will severely damage crops in the other phase eg canola, lupins and peas. Many of the herbicides listed here will also cause damage to other plants if they are applied in such a way that allows them to move off-target. Plant damage aside, allowing your spray to drift over your neighbour's property is likely to cause disputes, and is a breach of their rights under common law.

Wind is the usual vector for movement. Never spray when a moderate to strong wind is blowing, even if the immediate downwind area is free of susceptible plants. Spray can drift many kilometres under windy conditions. Another factor is spray droplet size. If you do your own spraying, ensure your spray nozzles and pressure are set to not produce a lot of fine droplets. The supplier of the equipment will be able to assist with this. The herbicides with the greatest potential for off target damage are the phenoxy group (see I below). Grapes, tomatoes, roses and many other common plants are very sensitive to these compounds. To complicate matters, as organic acids they are produced in two formulations - amine and ester, and the ester formulations come in high and low volatile variants. High volatile formulations can damage plants just by the vapour they release. Leaving an open drum near tomato plants will kill them. The use of these products near sensitive crops is controlled by the restricted spraying act.

Restricted spraying act

This act covers the use of 2,4-D, MCPA and similar herbicides in areas where sensitive crops are common.

The parts of the act that apply to Avon valley smallholders are:

• High volatile ester formulations cannot be applied within 10 kms of a commercial vineyard or tomato garden.

• A permit is needed to apply other formulations within 5 kms of the same enterprises. (permits are issued by your local Department of Agriculture office).

Herbicide resistance

In some cases, repeated use of the same herbicide has resulted in weeds that were originally susceptible to that herbicide becoming resistant. This occurs as a result of genetic variability in the original species population, some plants being more susceptible to the herbicide than others. After repeated use, the most susceptible plants are removed and all that remain are the tolerant ones.

To assist users in avoiding such a situation, herbicide manufacturers have adopted an alphabetic system of classifying their products by their mode of action. By alternating between suitable products from different groups, the potential for resistance development can be reduced.

The products below, which are referred to in the text above, have been grouped according to their mode of action codes. The groupings are completely arbitrary. A Group A product is not necessarily better or worse than a Group I product. Any long term control program, such as the spraying of Paterson's curse each year, should aim to use products from different groups in each year.

A. Grass selectives

These products affect grasses (family Poaceae) almost exclusively. There are at least products commonly used in broadarea agriculture. Some are selective enough to control wild oats in wheat and barley crops, while others kill most grasses and are used in horticulture, pulse and canola crops. For smallholders, their most common use would be to remove unwanted grasses from pastures and native bushland. Consult a specialist to determine the best product for each specific situation.

These products are leaf absorbed, so remember that perennials such as love grass and couch need to have plenty of fresh, green leaf material for the treatment to be effective.

B. 1. Sulfonyl ureas, 2. Imidazolinones, 3. Sulfonamides 1. Chlorsulfuron (Glean, Siege etc), metsulfuron (Ally, Brushoff etc) are widely used by farmers for weed control in cereal crops. They are the best choice for control of cape tulip and Guildford grass. For smallholders, they are also an option for control of Paterson's curse and oxalis species.

Their downside is their extreme toxicity to clovers and other legumes, and their residual effects. They will affect any legumes planted in the year of application, and possibly the next year as well in the case of chlorsulfuron.

Used in pasture then, they will remove most broadleaf and bulbous weeds, but will leave grasses. Thus some grazing will be available, which will not be the case if glyphosate were used.

2. Imazethapyr (Spinnaker) is similar in its mode of action, but is safe to use on clover pastures. It will remove many broadleaf weeds and most grasses. Grazing will therefore be substantially reduced for that season unless the clover is thick. The treatment will however allow the clover to set a lot of seed.

Not safe on medics, and relatively expensive.

3. Flumetsulam (Broadstrike) is similar to Spinnaker, but does not affect grasses and is safe on medic and lucerne as well as clover. Thus it will control or suppress most broadleaf weeds while allowing grasses and pasture legumes to flourish. Depending on whether the grasses present are useful or not, it may therefore be a better or worse choice than Spinnaker. It also is relatively expensive.

C. Triazines

Simazine and atrazine are in this group. They are root absorbed herbicides that have residual activity for up to a year. Widely used in farming for weed control in crops, atrazine's main use to a smallholder would be for chemical firebreaks.

By spraying rather than ploughing to produce the break, the risk of erosion is greatly reduced. The smoother soil surface is also less likely to catch moving weed seeds, and after several years of such control the break will need very little annual maintenance. Simazine can also be used on firebreaks, and is a better choice on sandy soils where its lower solubility will minimise leaching. Both products have little effect on established weeds, and glyphosate should be mixed in to provide control of these. A suitable mix is glyphosate at 1-2 l/ha plus atrazine or simazine at 5-10 l/ha.

Simazine can also be used to remove silvergrass from pasture. This grass is quite shallow rooted, and sensitive to triazine herbicides. Thus low rates can selectively remove it without damaging clovers or other grasses.

F. Nicotinanalides

Diflufenican is the main chemical in this group. Its most useful products are mixtures (Jaguar, with bromoxynil and Tigrex, with MCPA). These will control a range of broadleaved weeds in clover pastures without doing too much damage to the clover. They have no effects on grasses. Tigrex cannot be used in restricted spraying areas.

I. Hormone herbicides

A group of herbicides that act as artificial plant growth hormones. Plants treated with these herbicides are characterised by twisted or curled leaves. The plant's growth becomes uncontrolled and has been described as "growing itself to death".

They affect dicotyledons (broadleaf plats) and bulbs, but have little effect on grasses. Mixtures of these herbicides with those of Group C (above) are often synergistic ie the mixture is more active than would be expected. Thus weed control can be achieved with lower amounts of herbicide.

Because of their extreme activity on many desirable plants (see Off target damage above) users should exercise extra care when using any of these products. Their use must also follow the Restricted Spraying Regulations.

Products in this group include 2,4-D, MCPA, 2,4-DB, MCPB, dicamba, Garlon, Grazon, Tordon M. Glyphosate.

Commonly referred to as "Roundup", the brand name of the first such product available, this is the world's most used herbicide. Its two great advantages are its very low animal toxicity and the fact that it affects (almost) all green plants. Farmers use it widely for these reasons, both to control seedling weeds before sowing crops, to prevent seed set of undesirable species in pastures, and for weed control around buildings and fences. Glyphosate is absorbed through green bark and leaves. It translocates throughout the plant, killing roots as well as top growth. Glyphosate tends accumulate in storage organs such as tubers and corms, and so is very effective against plants such as sour-sob and watsonia. In some cases, treated plants will die off but appear to reshoot next season. The stored glyphosate then begins to work again and the weed dies.

Avon Valley smallholders could find it useful for weed control around fruit and other trees, buildings, firebreaks, and for weeds in paddocks as a first step in pasture establishment.

There are a multitude of brand names available, with a range of glyphosate concentrations. For example, "Roundup" has 36% glyphosate in solution while "Zero" has 10%. Check the concentration as well as the price when comparing products.

N. Glufosinate

A relatively new product, sold as Basta, and used mainly in horticulture. It is relatively expensive.

Glufosinate does not translocate to the same extent as glyphosate. It will move throughout the leaf into which it is absorbed, but not between leaves or into roots. Thus it is most effective against small seedlings without extensive roots. It is also effective against bulbous weeds.

Its main use currently is to mix with glyphosate. This will result in improved control of plants such as cape tulip and mallows.

Blanket wiping

As an alternative to spraying, herbicides can sometimes be applied to advantage by wiping them onto the target plants. Thick, absorbent material (more like a carpet than a blanket) is arranged to hang from a horizontal frame, and saturated with a concentrated solution of the herbicide using micro-sprayers or drippers. As the blanket is driven across the weeds, the herbicide solution is wiped off onto their leaves.

Obviously the technique is restricted to tall weeds, but good selectivity is available when the weeds are taller than desirable plants. Excellent results have been achieved with chlorsulfuron on Guildford grass, cape tulip and Patterson's curse growing in clover pastures, where the chlorsulfuron would kill the clover if it was applied as a spray. The height differential between the pasture and the weeds is even greater if the pasture has been grazed, as sheep will keep the clover short while ignoring the weeds. Glyphosate (1-2 litres diluted to 5 litres) and chlorsulfuron or metsulfuron (1-5 grams to 5 litres) are the chemicals most often used.

Blanket wiping can also be used to control weeds between the rows of orchards and vineyards where spraying would be dangerous to the trees and vines. The Department of Agriculture Farmnote 90/96 "Blanket wipers for tall weed control" by John Peirce and Brad Rayner gives full details of making and using this useful machine.

Spot spraying

A lot of spraying is done with hand-held garden sprayers. These are particularly useful for treating isolated patches of weeds, or even individual plants, but suffer from very inexact application rates. The application rate equates to about 1000 l/ha. If using the usual 1% glyphosate solution, a rate of 10 l/ha is applied, much more than is necessary to kill most plants. However, since the sprayed area is usually small, the inconvenience of repeating the spraying if it is unsuccessful far outweighs the cost of excess herbicide.

When using a hand spray, keep the spray as fine as possible without causing excess drift. Always wear waterproof gloves, and work upwind, walking backwards.

Mechanical methods

Cultivation

Mowing, cutting, slashing

Patterson's curse and wild oats are the easiest targets, with lower growing species such as barley grass and capeweed needing to be mown closer to the ground. Very low species such as corkscrews and silver grass need a level, rock free paddock for the technique to be used.

Annual plants have an urgent need to reproduce, and will recover from one mowing quite easily in most years. The next phase of growth will not be as tall as the first, nor is the capacity to produce seed as high, but some will be produced. Thus a mowing program will involve two or three cuts in most years, until the soil has dried to the point where regrowth is not possible.

If you are unable or unwilling to repeat the mowing, consider spraying the plants with glyphosate about 5 days beforehand. This will substantially reduce the regrowth. Doublegees cannot be fully controlled by mowing, as they produce seeds too early and too low for complete control.

Grazing

It is not sufficient to just put the sheep in the paddock at a standard stocking rate and forget them. Pasture species have evolved to survive under such conditions. Ryegrass for example will produce seed heads flat on the ground where they will avoid being grazed. The paddock must be grossly overstocked for about a week and then spelled to allow the weeds to regrow. It is then restocked. A whole farm program must be planned with paddocks being crash grazed and spelled in rotation until the season ends.

Care is needed with toxic plants. Sheep will not thrive if they have nothing but Patterson's curse to eat. If the paddock contains cape tulip, the sheep will need to be removed before they are forced to eat that.

Spray grazing

At the break of the season, when most plants have 2-6 leaves, all stock are removed and the area sprayed with 500 ml/ha of 2,4-D amine. This rate will not kill any plants, but it will alter the metabolism of many broadleaf plants and increase the level of sugars in the leaves. The leaves are also twisted and curled up, making them more accessible to grazing animals. Clovers are not affected as much as capeweed, doublegee, corkscrews or Patterson's curse.

After a week, sheep are put in the paddock, whence they actively select the weeds to graze and leave the clover. This allows the clover to get a head start on the other species, and it will increase its percentage among the sward. The procedure is repeated for a number of years until a clover dominant pasture is attained.

Remember - a permit is needed if you are within 5 km of a commercial vineyard or tomato crop.

Solarising

Just after the opening rains, when the first flush of weeds has emerged, cover the soil with a sheet of clear plastic. Fix down firmly and leave for several days until the seedlings have visibly deteriorated. As the technique relies on solar energy, it is more effective in autumn than in winter. The soil may be irrigated to stimulate germination if the natural rains arrive too late.

The heating effect will not penetrate far into the soil, so large plants will regrow from their root systems.

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