Method of Controlling Vegetation

Background of the Invention

The present invention relates to a method of controlling vegetation having persistent roots or rhizomes, where rhizomes are underground shoots.

Invasive weeds cause many problems, including penetrating concrete structures, roadways and housing developments, as well as preventing other more desirable species from flourishing. Many of these weeds are very difficult to control, given that they have persistent roots or rhizomes. One specific problem caused by persistent roots or rhizomes is that the weeds are able to regenerate from a small portion of the roots or rhizomes. If, during attempts to control the weed, these persistent roots or rhizomes are damaged in any way, this damage actually encourages recovery growth, given that this is one of the weed's methods of reproduction. Japanese Knotweed is one such invasive weed. It grows very densely and is extremely destructive. It grows to around 3 metres tall above ground and has a rhizome system underground that extends out up to 7 metres from the plant and up to 4 metres downward into the ground. It also has a dense mass of root-like material which sits at the surface of the soil called the crown. Japanese Knotweed is a particular problem near watercourses where dense clumps can block drainage channels and inhibit the growth of native species. It is estimated that the cost of control for Japanese Knotweed in the UK runs into several billion pounds. The weed is resistant to conventional weedkillers and control by chemical means requires repeated applications over many years. The most effective chemical treatments are not suitable to be used near water or trees, because of their toxicity.

The form of control which is currently most widely used is the chemical glyphosate. Glyphosate can only be used when the plant is in full leaf, and therefore can only be used once or twice per season. It generally takes five to ten years of treatment to fully kill the weed, although the weed can go into a dormant state more quickly than this. It can then remain dormant for anything

up to 25 years. In the dormant state the knotweed will reappear if the ground is disturbed in any way. A further problem with glyphosate is that its use often results in the knotweed growing back looking like a miniature version of its former self, with much smaller stems and leaves. This means that the general public often mistake this miniature version for a different plant, and therefore do not re-treat the weed. The knotweed then quickly grows back to its original size and its treatment has to start again from scratch. Some formulations based on glyphosate can be used near watercourses but controls on residual chemicals allowed in drinking water supplies prevent these being used in many of the areas where the weed grows.

Another known approach to the knotweed problem is mechanical destruction of the plant. This could be the cutting down of the plant or covering it with an impenetrable membrane. There are two major problems with this method. The first is that because the weed keeps large reserves of energy below ground, it takes approximately 10 to 15 years to eradicate the weed.

Given the persistent nature of knotweed rhizomes this is highly undesirable because the plant is able to propagate from tiny fragments. This means if a field full of knotweed is cut down and the rhizomes pulled up, every last fragment must be removed and the soil removed or replaced to prevent re- infestation. This is clearly a huge drain on resources.

A further known method of control is biological control. This involves introducing an organism, for example an insect or a virus, which is known to be destructive towards Japanese Knotweed. Use of biological methods is not yet effective enough to control knotweed without also using other methods.

Brief Summary of the Invention

According to an aspect of the present invention, there is provided a method of controlling vegetation having persistent roots or rhizomes comprising the steps of: applying electricity to said vegetation to effect current flow through said roots or rhizomes so as to traumatise said roots or rhizomes and thereby stimulate recovery growth; and after a period of recovery growth,

performing a second destructive treatment upon said vegetation.

Brief Description of the Several Views of the Drawings

Figure 1 shows a site infested with Japanese Knotweed, ready to be treated according to the present invention;

Figure 2 shows components contained in trailer 102 and applicator 103 as shown in Figure 1;

Figure 3 shows an operator treating Japanese Knotweed according to the present invention; Figure 4 shows a schematic cross-section through a Japanese

Knotweed plant;

Figure 5 shows a damaged rhizome;

Figure 6 shows the rhizome shown in Figure 5, with some recovery growth; Figure 7 shows a second treatment being applied to the Japanese

Knotweed; and

Figure 8 shows removal of the crown.

Written Description of the Best Mode for Carrying out the Invention

Figure 1

Figure 1 shows a site infested with Japanese Knotweed, which is to be treated using a method according to an embodiment of the present invention. Depending upon the time of year and the level of infestation, a pre-treatment step involving the use of chemical or mechanical control may be included before the electrical treatment is conducted.

Operator 101 arrives at the scene with trailer 102. Trailer 102 contains electrical equipment which is detailed in Figure 2. Operator 101 is holding an applicator 103 which is linked to trailer 102 by cable 104. Operator 101 is preparing to treat the Japanese Knotweed shown at 105 with applicator 103, as explained in the description of Figure 4 below.

Figure 2

Components contained in trailer 102 and applicator 103 are illustrated in Figure 2. A generator 201 generates electricity which is passed to transformer 202 which is in turn linked to control unit 203. In the present embodiment components 201 to 203 are contained in trailer 102, although in alternative embodiments one or more of these components are contained in a unit which can be carried by the operator, such as a backpack type device, or incorporated into the applicator 103 itself. In a further alternative embodiment, the equipment is scaled up such that applicator 103 is incorporated in a vehicle, such as a tractor. Switch 204 connects to control unit 203, and serves to switch the current flow on and off. In this embodiment switch 204 is contained in applicator 103.

Figure 3

Figure 3 shows operator 101 applying electricity to a Japanese Knotweed stem 301, according to the present invention. Applicator 103 is positioned so that its conductive treatment portion 303 is in contact with stem 301. Applicator 103 is manufactured to be of a suitable length to ensure both ease of use and operator safety. When switch 204 is in the "on" position, electricity is supplied from generator 201 , along cable 104 to applicator 103. In a preferred embodiment operator 101 checks the area before treatment for metal debris which might accidentally be contacted in the ground nearby. Depending upon the configuration of the equipment, it may be necessary to undertake a calibration process of determining the correct voltage level for a specific plant before treatment can begin. This may be in the form of trial and error applications, or may be automated in some way. In the present embodiment, the experience of the operator is relied upon in selecting the correct voltage level. If the voltage level is too high there is danger of the current arcing back to earth (either straight from applicator 103 or from part way down stem 301). This means that the current hasn't been transmitted

down into the roots or rhizomes and therefore recovery growth will not be stimulated. Alternatively, if the voltage is too low the current will not be passed down into the roots or rhizomes.

The voltage required to initiate damage to the stem when the applicator is first applied is often much higher than that required to continue the process. When cells in the stem burst, and cell electrolytes are released, the plant stem impedance decreases. Because of this effect, in an embodiment of the present invention the voltage applied is varied to achieve a controlled current as the plant becomes gradually more damaged. Control unit 203, in this embodiment, measures the degree of damage as it takes place and controls the current through a feedback loop. Use of a controlled current also assists in avoiding generator overload.

In an alternative embodiment, it is desirable to begin with a relatively low voltage and build up the current flow gradually. This approach is particularly useful if the plant stems are wet, or if weed control is being carried out in an area where there may be metal debris in the ground nearby. In a further alternative embodiment, a combination current waveform is used. An example of this is that one or more high voltage pulses are output to initiate the stem damage, with application of controlled current inbetween. This serves to maximise the damage to the plant without putting undue strain on the generator.

Cable 104 enters applicator 103 at the end of its insulating handle 302. Electricity is passed from cable 104 to conductive treatment portion 303, which passes through a bore of insulating handle 302. In alternative embodiments there is an insulated portion which does not form a handle, for example if applicator 103 is mounted onto a tractor.

A potential is applied to the stem 301 to effect current flow down through the root or rhizome system below the ground, which therefore forms part of the electrical circuit back to the generator. In this embodiment, a potential of approximately 2 kilovolts is applied, although in alternative embodiments a potential of any magnitude greater than 100V would be applied. In the present

embodiment this current is an alternating current with a frequency of 50 Hertz. The frequency used in alternative embodiments would vary according to the generator used. In alternative embodiments a direct current is used instead.

Figure 4

Figure 4 shows a schematic cross-section through a Japanese Knotweed plant. Applicator 103 is placed into contact with stem 301, and in this embodiment operator 101 would then operate switch 304 in order to apply electricity to stem 301. The electricity passes down stem 301 (below the site where applicator 103 touches stem 301) and into crown 401. Crown 401 is a large mass of root-like material, which sits at the surface of the soil. From crown 401 the electricity passes into the rhizome system 402. An enlargement of a rhizome that is part of system 402 is shown in Figure 5. Electricity is applied through applicator 103 to stem 301 to effect visible damage to the stem. In a preferred embodiment, the water in parts of these upper parts of the plant becomes superheated and therefore vaporised, causing stem 301 to collapse. In an alternative emboidment, treatment continues until all visible parts of the plant which are above ground appear to be dead. However, in further alternative embodiments, the damaged stems are left to dry out, or removed by other means such as mechanical cutting. All parts of the plant above ground need to be destroyed because the weed would otherwise re-grow from even the smallest remnant, due to its .infectious nature.

Figure 5 Figure 5 shows a rhizome which has been damaged by the passing through of an electric current in accordance with the present invention. Damage has occurred at points 501 and 502. The result of this damage is shown in Figure 6.

Figure 6

Figure 6 shows the rhizome illustrated in Figure 5, after recovery growth has

begun.

Because knotweed has persistent rhizomes, wherever damage occurs, the rhizomes will bud and recovery growth will begin. Therefore, at each of the points 501 and 502 where damage had occurred, new growth is now emerging as shown by shoots 601 and 602.

The growth of shoots 601 and 602 uses up some of the energy stored in crown 401 and rhizome system 402. Given that the parts of the plant which were above ground were destroyed by the application of electricity, the plant now has no means for generating further energy, as it cannot photosynthesise without its leaves. This means that by inducing recovery growth and killing the parts of the plant which are above the ground, the method is forcing the knotweed to use its reserves of energy and therefore eventually "burn out". Although the presence of recovery growth means that the knotweed is not destroyed immediately, after repeated treatments the knotweed gradually runs out of energy reserves and will eventually die. This is achieved significantly sooner than eradication would be achieved by purely chemical means. As Japanese Knotweed grows very rapidly, within a timeframe of approximately two weeks to a month the shoots 601 and 602 will be sufficiently strong to be treated again. This is shown in Figure 7.

Figure 7

Figure 7 shows one option for a second treatment of the knotweed.

As is shown in Figure 7, when the recovery growth (as illustrated in Figure 6) emerges from the ground it is much weaker and more spindly than the original knotweed plants. This weaker regrowth is treated, either by re-application of electricity as described above, or, depending upon the location of the infestation, it can be treated with a chemical such as glyphosate, or by mechanical treatment such as cutting.

In Figure 7, operator 101 can be seen to be treating regrowth stem 701 with applicator 103. In a preferred embodiment, the application of electricity is repeated several times, each time the regrowth becoming weaker as the

reserves of energy held in the crown are depleted.

Figure 8

Figure 8 is an embodiment of the invention showing removal of the crown 401. After repeated treatments as described in Figures 1 to 7, possibly including some treatments with glyphosate or a similar chemical, the crown 401 or rhizomes 402 will have no remaining reserves of energy with which to effect recovery growth. At this point the crown 401 and/or rhizomes 402 can be removed from the ground by operators 101 and 801 and taken away from the site. In alternative embodiments, crown 401 is be removed by other means, such as earth moving equipment.

Because the present invention involves causing recovery growth and therefore uses up the reserves of energy, the crown is unable to go into a dormant state as it can with other methods of control. In a preferred embodiment the crown is incinerated after removal.