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III. GENERAL METHODS OF WEED CONTROL A. HERBACEOUS WEEDS Limiting disturbance Herbaceous weeds are favoured by disturbance, particularly that which bares soil. An important element of control is to prevent or restrict the recurrence of such disturbance. Several of Canberra�s weeds such as Common Sow thistle, Prickly Lettuce, Fleabane and Indian Hedge Mustard only become problems in heavily disturbed places. Plants that only dominate in disturbed areas are called ruderal weeds. Direct methods of control The general aims in controlling a herbaceous weed) are to do one of the following: a. to remove the whole plant from the soil; b. to cut off the stem near the base; c. to spray the plant� usually at the rosette stage; d. to remove and destroy all seeds produced. Most herbaceous weeds will grow again if the stem is cut off early in the season. So b) is liable to be only temporarily effective and has therefore limited application. Nevertheless b) is an important method for control of thistles, as mentioned below. A. Manual methods Slashing. There are more and less sophisticated methods of slashing. The simplest is just to cut the stem off with secateurs (small or large) or any other sharp implement such as a sickle, scythe or even a spade with the edges (rather than the tip) sharpened. The most sophisticated and speedy method is using a brushcutter. The plant may wither and die after this treatment; or it may grow again. The outcome depends on the plant species, the time of cutting, and the subsequent climatic conditions. Most weeds will grow again if simply cut off. But they are more liable to die if i) cut after flowering has begun ii) cut at the very base i.e. level with the ground (particularly, below the first lateral leaves); iii) cut in the autumn iv) severe climatic conditions then prevail e.g. no rain; or severe frosts. As examples of the influence of plant type: Thistles (all the larger ones) mostly die off if cut at the base; but saffron thistles will continue to grow if cut in summer before flowering begins. Brushcutters �with nylon blades attached � enable the skilled operator to slash much larger areas (up to 10 times more) than slashing by hand. However there are limitations with nylon blades that are apt to be twisted off the rotating head if the plant stem is too tough (or if the blade strikes a stone or piece of wood). Thus, all the larger thistles in the list, and also the more tough and old saffron stems, may cause the blade to spin off. It is better to cut these off with loppers or better still, chip them out with a mattock. The brushcutter is particularly useful when there are large areas of weeds going to flower and seed in the near future � in an area too large to be hand-weeded (which is by all means more efficient, but very slow). Hence, there will probably be an initial phase in a large area where one is attempting to control the saffrons, where slashing with brushcutter will probably be the first choice. Later, when the weeds are fewer, hand-weeding will be preferable because it removes the weeds altogether. Some tips on the use of brushcutter are found in Appendix 3, but this is not a complete guide on how to use a brushcutter. Persons wishing to operate a brushcutter should undergo an initial practical training in handling and maintaining the equipment. Pulling-out is the most straightforward method of all; but if the area is large, it is slow and hard work. A good pair of tough gloves is needed. For thistles and other thorny weeds, gloves like welders� are best. Advantages: a. Pulling-out normally removes the weed once for all (unless a major root fragment is left in place). b. It is generally a bit quicker than digging out. c. It does not disturb the soil as much as digging out; it does not disturb adjacent native plants including grasses. d. Most weeds can be pulled out, even if mature and large; but this can be difficult if the soil is dry. e. A useful contribution can be made casually e.g. when meeting weeds during a stroll. Disadvantages: a. It is very slow compared with slashing � unsuitable for large areas e.g. several hectares of thistles b. Not possible for rosettes (which may however be cut with loppers/secateurs at or preferably below ground level c. The roots of some weeds may survive pulling e.g. St John�s wort, Paterson�s curse, skeleton weed. Digging out is usually best done with a mattock; but can be done with a mini-pick (which is really a mini-mattock), spade, trowel or lawn-weeder fork. The mini-pick is particularly useful for digging out rosettes of thistles or other herbaceous weeds. The mini-pick can be handled with one arm; this is sometimes an advantage, but that arm eventually becomes tired. For most purposes a light-weight mattock (Garden Mattock) is best.It has a usual-type mattock blade on one side and a narrower blade (like the broad end of a pick blade) on the other. The handle needs to be inserted and fixed careflly with wedge and glue.(Contacet Vernon Bailey for help/advice if needed). Advantages: a. By inserting the mattock blade wide (e.g. 10 cm) from the base of the stem, one can loosen the soil below the bottom of the root, and thus pull out the entire root system � even without displacing any grasses growing there. b. Can be done when the plant is too big to be pulled out, and even where the soil is relatively dry; also where the stem has been pulled and the stem bro ke off. c. Is the best method for dealing with rosettes (re-growth may occur if cut off). Tips on pulling and digging: Pulling is easiest and most effective shortly after a good rain � less likelihood of stem- and root-breakages When pulling, hold the stem with both hands, the fingers of one of them right at ground level If there is resistance, pull first to one side then the other, then forwards and backwards � this often helps it to slip out of the ground A quantity of soil often adheres to the roots; this may be enough for a plant to produce viable seed from a flowering plant, so the soil should be vigorously shaken off Replace any ground cover e.g. grasses disturbed Digging out is usually best done, in field conditions, with a mattock; but care should be taken to dig deep enough not to cut the taproot off short Making small piles of the removed weeds or rosettes helps to minimize missing areas needing to be weeded Pulling out an annual plant is no use if it has already gone to seed. Collecting and bagging flowers and seedheads If large numbers of weeds are flowering or have gone to seed but the seed is not yet dispersed, it is desirable to collect the flowering heads or large buds in large tough bags (the type with tapes) (not soft garbage bags). Such weed collections can be taken away (e.g. by CNP/CUPP) to be destroyed by fermentation. Home-gardeners can compost them in the backyard. NB . Note that mechanical removal by any means � pulling, slashing, digging out � will have limited success if the weed has already gone to seed or is in flower or advanced bud stage. Under these conditions if the flower or seedhead is left on the ground the seeds are likely to mature, grow and produce a further crop of the weed. Not rarely, one may be overwhelmed by a large area of thistles going to seed in (say) the spring/summer. Normally, if left alone, the seedheads will stay on the stalks for several months before falling to the ground or being dispersed by animals or wind. At any time during this process � usually autumn or winter, or early spring � the seedheads may be collected and disposed of safely. This will very substantially reduce the next crop � even though some seeds will have already dropped to the ground. In practice this process is too laborious for saffron thistles � unless few in number; but is suitable for the large thistles. Thus in practice, at most times of the year it is not a case of one approach only, but of at least two, at least for the large thistles. For instance, chipping out rosettes will be combined with digging out mature thistles and bagging the seedheads. If dried-up seedheads predominate (e.g. winter work), besides collecting those, the nearby ground should be searched for rosettes, which are then chipped out. The practical implication for the volunteer is the need always to carry around a tough bag for seedheads, almost year-round. Home-gardeners will be generally able to deal with all thistles present by pulling out; if necessary using a knife inserted in such a way as to cut out a cone of soil around the roots, as described in the ACT Bushcare Manual pp.113-116. (See also an important special note on Bathurst burr. ) B. Chemical methods Chemical methods are particularly useful with large areas of weeds in dense patches. Weed-specific chemicals are available for many weeds; but often they have adverse effects on native plants e.g. forbs. So their use is generally recommended only where the problem cannot be solved by manual methods given above. Chemical control of large patches of thistles is probably the most common application. i) Boom-spraying may be indicated where a large area of thistles is to be controlled. Spraying - using a high concentration - is done from a vehicle over the whole area. ii) Spot spraying can be done from a knapsack , or from a motorized pump using a long hose. Knapsack spraying is a selective spraying done by hand, walking in among the weeds. Spraying usually has to be done in the early growth phase, e.g. spring �before flowering. In spring there is usually prolific growth of grasses. If so, the spray will not reach the rosettes of saffron thistles effectively. Some form of grass-cover control is therefore necessary first e.g. mowing or controlled grazing, Once a substantial area has been sprayed, there is liable to be a dense invasion with a variety of weeds, sometimes very difficult to control. General guidance on use of sprays The ACT Bushcare Manual, pp. 140-143 gives advice on use of sprays, including a checklist of 15 rules to be observed � summarized as follows: Do not use herbicide before receiving training Do not use herbicide when the plant is stressed in any way Do not spray on public land unless you have the consent of the land manager Do not spray weeds in the heat of the day, during drought, extreme cold or when it is windy Do not spray weeds when rain is expected within 6 hours Do not use herbicide on a plant damaged in any way (e.g. lopped, burned or broken) or which has recently been treated with herbicide Do not repeat herbicide treatment too soon Do not be impatient and dig up the plant before the roots are completely dead Do not allow the herbicide to come into contact with non-target plants Do not allow the chemical to get contaminated with dirt; keep all equipment clean Stick to the label recommendations as regards dose Do not mix glyphosate with other chemicals unless specified on the product label Do not allow any chemical to come in contact with skin or eyes; avoid inhaling drifting spray Do not spray in shorts or T shirt � wear suitable clothing & use protective equipment Do not ignore commonsense factors; always err on the side of caution. Important limitations on use of herbicides The use of herbicides is generally beyond the scope of volunteer workers in Canberra Nature Park and Canberra Urban Parks and Places, other than the use (by CNP volunteers) of glyphosate for �cut and dab� treatment of woody weeds (see pp.[29-30] ). Glyphosate is a general herbicide and metsulfuron a specific herbicide. Both are used for the control of certain broad-leaf and other environmental weeds. Herbicides are to be used only by trained and qualified CNP/CUPP staff or contractors authorized to use them; with the exception that CNP volunteers may use glyphosate only (administered from a spray-bottle or weed-brush), for dabbing on the cut stems of certain woody weeds. The use of herbicides is regulated by the National Registration Authority (NRA) for Agricultural and Veterinary Chemicals (address in Canberra: Ground Floor, John Curtin House, 22 Brisbane Avenue, Barton ACT 2600). The authorized uses are clearly listed in the �Label� of the product - a document specifying all authorized uses. The NRA also issues special Permits for the minor off-label use of a registered Agvet chemical product. Leaflets or booklets are published by manufacturers of herbicides, specifying the authorized uses and the conditions for effective use of the product in agricultural and other areas, the annual and perennial weeds controllable, the volume or concentration of application, and other critical comments, etc. These uses are reviewed and revised every 2 years by NRA. CNP/CUPP weed specialists are in a position to advise parkcare/landcare groups on the latest recommendations and approved uses of herbicides. Home gardeners should be able to obtain reliable up-to-date information from Garden Centres. For some more details relating to particular weeds, where use of chemicals is sometimes virtually essential, see (in #IV) Saffron and Variegated Thistles; Paterson�s Curse, St John�s Wort, and Skeleton Weed. B. GRASSES There are three groups of grasses relevant to control methods. * Annual grasses tend to dominate frequently disturbed areas and areas with high soil nutrient and/or moisture levels, such as the base of big trees or under Cootamundra wattle. Annual grasses grow during the spring and autumn months and will generally not replace summer growing perennial native grasses. Control is generally to be achieved by limiting disturbance or reducing moisture or nutrient levels. * Pasture or lawn grasses such as phalaris, cocksfoot, perennial rye grass and tall fescue tend to remain as dense patches in areas where they have been deliberately introduced. They spread relatively slowly outwards from these patches. # Isolated plants: digging out with a mattock can be effective and can reduce the edges of an infected area. # Well established patches: replacement with native species is problematic. Some success with i) slashing (e.g. with mower) and then seeding patches with native grasses (see below); ii) spraying; and iii) native tree plantings. � Aggressive exotic perennial grasses such as Serrated Tussock, Chilean Needlegrass, African Lovegrass and Yorkshire Fog are capable of invading and dominating much of Canberra's bushland. Prevention: Vigilance for early introductions is critical to control. Machinery hygiene, particularly of mowers, is another crucial factor in reducing the spread of these species. Control: i) Isolated plants can be dug out with a mattock. ii)Spot spraying is also effective control method. Once these grasses are well established spray programs are the only effective way of significantly impacting on their extent. Replacement of exotic grasses with native species A series of experimental trials aimed at replacing exotic grasses and herbs with native grasses have been conducted by the National Parks Service of Victoria. i) Seed-bearing Kangaroo Grass (Themeda australis) hay was cut, during summer, by mowers that cut close to plant bases and left the hay on the ground. Hay was immediately raked into piles and placed into wool bales. The hay was then placed over a recently slashed paddock dominated by annual grasses, Phalaris and Serrated Tussock. The hay was laid so there was just enough to cover the ground so that no spaces were visible. Aggressive perennial weeds, such as serrated tussock, were also spot sprayed. The trial sites developed an average cover of 31% Themeda within a few years. ii) Similarly seed of Tussock Grass (Poa labillardieri) was applied to a slashed Phalaris paddock. With no further treatment, within 10 years the trial plots were dominated by the native Poa. iii) Similar application of seed of Silky Blue-grass (Dicantheum sericeum) and Red-leg Grass (Bothriochloa macra) achieved some success at replacing exotic grasses with these native grasses. Reference: McDougall KL. The establishment of native grasses at Organ Pipes National Park near Melbourne. Submitted to: Journal of Ecological Restoration and Management, 2002. C. WOODY WEEDS Methods of control are similar for most woody weeds and are briefly summarized in these 2 pages. In the texts for specific woody weeds, details or different methods are indicated where appropriate. A. Manual methods Pulling out is in general, only feasible for very small seedlings (up to about 10-20 cm high) - and only when the soil is moist. With larger plants there is too much risk of breaking off the stem or root, that will then normally grow again. Digging out, usually with a mattock, is occasionally an option for small plants. But there is usually again too much risk of breaking off the root, and subsequent re-growth (e.g. blackberries). Cutting off, alone, is sometimes effective. This is normally the case with, for instance, Radiata Pine or Cootamundra Wattle � provided the cut is at ground level. But most exotics tend to grow again when cut off. For small trees and shrubs, large loppers or secateurs are usually sufficient. For medium-size trees (stem diameter >4 cm) a hand-saw is used: e.g. pruning saw or bow saw. For larger trees (> 10 cm) a chain-saw saves much hard work! But volunteers must be given a formal training for this before being allowed to use it. Ringbarking is a better alternative for large trees. Make two circular cuts right around the trunk, a few cm apart, and remove all the bark in between. This leaves the tree still standing � an advantage if small birds have used it for nesting etc. B. Chemical methods The usual method, for the great majority of woody weeds, is the cut-and-dab method: Cut off the trunk or stem as low down as possible, using secateurs or saw as described in previous section. Immediately apply a general herbicide, e.g. glyphosate. The herbicide is mixed with a red dye to show up the area treated; and diluted with water, as described below. The mixture is applied as quickly as possible after cutting, because after about 30 seconds a scab forms on the cut surface, making it difficult for the chemical to penetrate. Moreover chemical applied immediately will be drawn down into the root due to loss of transpiration pressure. Cut the stem should as horizontal as possible, to minimize run-off of the chemical. The dilution (in water) used varies according to season: one part of glyphosate to two of water in winter; 1:4 in summer � when growth is more active, and consequently the plant absorbs more of the poison. This chemical is toxic to humans also. Handle carefully, using impermeable gloves (e.g. rubber) and avoiding all skin contact. The chemical is applied using i) a spraybottle with a blunt nose; or ii) a weedbrush (see below). i) Spray bottle. The nose is applied directly to the cut surface, to minimize run-off on to neighbouring vegetation. Run-off is both wasteful and probably harmful to that vegetation. The spraybottle should not leak, and should not be used to spray from a distance. ii) �Weedbrush� or �weed wand�, available in hardware stores. The herbicide + dye mixture is loaded into a cylindrical chamber running the length of the weedbrush (capacity usually 350 ml). Swipe the brush tip over the cut stem in two directions at least to ensure it is fully coated with herbicide. For large trees, to avoid cutting off altogether, the procedure of frilling or chipping with painting-on of herbicide is advocated, or alternatively injecting the herbicide - see pp. 138-139 of ACT Bushcare Manual. A particular feature of creepers and climbers is that they tend to take root at multiple points. Sometimes the roots are shallow and can be pulled out whole at some of these points. But mostly vines are deep-rooted. Apply herbicide to all points where rooting occurs. More details are in the ACT Bushcare Manual p.139. With careful application there is practically 100% success in killing the plant. But success rates may be much lower in some cases e.g. bamboo, and also if it rains heavily soon after the application. The concentration of glyphosate, once made up with water, falls off by about 50% in one month. So in practice a fresh solution should be made up preferably each working day, or at least each month. Another chemical � a specific herbicide � useful for many common weeds is metsulfuron, diluted 10 g per 100 litres. This is sprayed on all the leaves. This spray is more powerful than glyphosate but more toxic to surrounding vegetation. It is mainly handled by CNP/CUPP staff or contractors; not by CUPP volunteers at all, and by CNP volunteers only after special training for it. In all cases it is advisable to look again, after a month or more, at any area treated, to identify and deal with any of the target weeds that have been missed. Go to Top of Page |