Patent Publication Number: US-2021169063-A1

Title: Weed control

Description:
The present invention relates to a method of controlling vegetation and to an apparatus for performing the method. 
     Conventionally, vegetation such as weeds is controlled either by physical removal, such as hand weeding, or by the use of herbicides. Hand weeding can be very hard work; but plants are becoming increasingly resistant to herbicides. In addition, there is increasing public resistance to the use of chemicals in the environment, and legislative changes to reduce use of toxic chemicals as herbicides. Therefore there is an interest in methods of controlling vegetation which do not use synthetic chemicals and which avoid hand weeding. 
     Thermal methods have been suggested for weed control. A variety of methods have been used to provide heat to weeds, for example, hot water, steam, hot air, flames and hot foam. These methods can overcome some of the disadvantages of herbicides such as spray drift and soil or groundwater pollution. WO 02/07513 (Waipuna International) describes a process for weed control by application of hot foam, in which hot liquid containing a foaming agent is supplied to an applicator head, and air is supplied from a blower through a hose, so a hot foam is created. NL 1018458 (Waterkracht BV) describes a process in which hot water is sprayed onto weeds, and an insulating layer of foam is then deposited onto the weeds that have been sprayed. 
     The present invention aims to provide a more effective weed-killing method and apparatus, which overcomes problems that have been found to occur in the production of a hot foam layer. 
     The present invention provides a method of controlling vegetation comprising the steps of: 
     generating a foam comprising air and an aqueous solution comprising a surfactant;
 
dispensing the foam so as to coat the vegetation that is to be controlled; and
 
then injecting hot water into the foam so as to contact the vegetation below or within the coating of foam.
 
     The hot water causes the vegetation to wilt and die, while the foam suppresses heat loss from the hot water. The foam may be generated and dispensed at a temperature above ambient temperature. Foam at an elevated temperature has the benefit that when the hot water is injected, it enters an environment that has already been heated up, so reducing the loss of thermal energy from the injected hot water. More of the thermal energy from the injected hot water is therefore available for raising the temperature of the vegetation, so the method is more effective at controlling the vegetation, for example when killing weeds. Preferably the foam is arranged to coat and surround at least a base part of the vegetation, so the hot water is injected adjacent to a portion of the vegetation that is near the ground. 
     The hot water may be at a temperature of at least 60° C., or at least 75° C., and may be at least 90° C., for example 95° C. or more. When vegetation is raised to such a high temperature, the proteins within the cells are denatured, and this kills the portions of the vegetation that are contacted by the hot water. When treating weeds, in some cases the result is that the weed will wilt and die. In some cases the portions of the weeds that are above the ground wilt and die, but new shoots may subsequently grow up from the roots, so that it may be necessary to repeat the weed-killing treatment. 
     By way of example the aqueous solution from which the foam is generated may include a small proportion of xanthan gum, which may assist in increasing tackiness, so the resulting foam tends to stick to the vegetation; a glutamic acid-based chelating agent, to sequester any polyvalent ions such as calcium ions which might otherwise inhibit foam formation; and a mixture of two different alkyl polyglucosides (APG), for example a shorter chain length APG, C8-C10, to efficiently wet the surface; and an APG of a wider range of chain lengths, for example C8-C14, to enhance foam formation. APGs are well known as surfactants, aqueous solutions of APGs forming foams; such APGs are available for example from Cognis™. 
     It will be appreciated that all of these compounds for use in the aqueous solution are naturally-occurring compounds, or are based on naturally-occurring compounds; and that they are readily broken down by microorganisms in the environment, so they do not cause contamination. The components of the aqueous solution may be provided in the form of a concentrate, and this concentrate then be diluted with water, for example hot water, during the course of the foam formation. 
     In a second aspect the invention provides an apparatus for controlling vegetation comprising a foam-generating device for generating a foam that comprises air and an aqueous solution comprising a surfactant; a foam-dispensing duct for dispensing the foam so as to enable a coating of foam to be deposited on the vegetation; and a nozzle for injecting hot water into the foam so as to contact the vegetation below or within the coating of foam, and means to supply hot water to the nozzle. 
     The apparatus may include means to delay the injection of hot water through the nozzle until after the foam has been dispensed from the foam-dispensing duct. 
     The nozzle for injecting hot water may be arranged to spray the hot water over surfaces of the foam-dispensing duct, for example by injecting the hot water at the top of a chute at an end of the foam-dispensing duct. It has been found that the foam tends to stick not only to the surfaces of the vegetation but also to surfaces of the foam-dispensing duct; and injecting the hot water in such a way as to spray the hot water over the surfaces of the duct tends to remove any remaining foam from those surfaces. The hot water may be sprayed through a nozzle shaped to form a water blade, that is to say a jet of water that is wide but thin, as this is particularly effective at removing all traces of the foam material from the foam-dispensing duct. 
     The foam-generating device may comprise an air blower connected to an air duct, with a liquid spray nozzle within the air duct. A flow duct to carry water leads via a venturi constriction to the spray nozzle, and a second duct communicates between a vessel to contain a concentrate for the aqueous solution and the venturi constriction, so that water flowing through the flow duct causes the concentrate to be sucked into the water flow at the venturi constriction, so that a diluted aqueous solution is then sprayed through the spray nozzle to mix with the airflow and form foam. The foam formation may be enhanced by providing a mesh barrier that surrounds the spray nozzle, so that the sprayed aqueous solution and the air then pass through the mesh barrier. 
     An alternative foam-generating device comprises an air blower connected through an air duct to a porous block, the porous block being arranged to be immersed in the aqueous solution in an open-topped vessel. In operation air from the air blower emerges from the porous block as multiple small bubbles, which form foam at the surface of the aqueous solution within the vessel. The continuous flow of air therefore continuously forms foam, and this foam therefore flows out of the vessel, so it reaches the foam-dispensing duct. 
     In each case it will be appreciated that the quantity of foam that can be generated is constrained by the quantity of the concentrate that is available, and in some cases may be constrained by the airflow available. The volume of foam is considerably greater than the initial volume of the concentrate, and indeed is greater than the volume of the aqueous solution that is formed from the concentrate. For example the volume of foam may be between 20 and 250 times greater than the volume of the aqueous solution, as the foam may for example be between 0.4% and 5% aqueous solution (by volume), although preferably no more than 2% aqueous solution (by volume). 
    
    
     
       The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: 
         FIG. 1  shows a perspective view of a weed control apparatus of the invention, partly cut away; 
         FIG. 2  shows a view, partly in longitudinal section, of the weed control apparatus of  FIG. 1 , 
         FIG. 3  shows a perspective view of an alternative weed control apparatus with a handle, partly cut away; 
         FIG. 4  shows a sectional view of part of the weed control apparatus of  FIG. 3 , apart from the handle; 
         FIG. 5  shows a valve mechanism within the handle of the weed control apparatus of  FIG. 3 ; and 
         FIG. 6  shows a sectional view on the line  6 - 6  of  FIG. 5 , showing only the lever arm and the rocker plate that are associated with the valve mechanism. 
     
    
    
     Referring to  FIG. 1 , a hand-held weed control apparatus  10  comprises a generally cylindrical body  12  at one end of which is an air blower  14 , and a protruding handle  15  which includes a trigger  16 . The air blower  14  may be powered by a battery  18  (shown in  FIG. 2 ), or may be mains-powered, the apparatus  10  being provided with a flexible lead (not shown). At an intermediate position along the cylindrical body  12  a bottle or jar  20  is attached by a screw fitting to the underside of the cylindrical body  12 ; and also a flexible hose  22  to carry hot water from an external heater or boiler  23  (shown schematically) is connected to the underside of the cylindrical body  12 . The opposite end of the cylindrical body  12  defines an open-ended tube  24 . An annular nozzle structure  25  is mounted at the open end of the tube  24 , from which projects an open-topped chute  26 . The type of external heater or boiler  23  is not critical, as the heater or boiler  23  may produce heat electrically, or using a gas or liquid-fuel burner, for example. 
     Referring also to  FIG. 2 , the air blower  14  when energised causes air to flow along inside the cylindrical body  12  and the open-ended tube  24 , so that it passes over a mist spray nozzle  32  (shown in  FIG. 2 ). The flexible hose  22  connects to a solenoid-controlled valve  42  within the cylindrical body  12 , and a duct  30  leads from the control valve  42  to the mist spray nozzle  32 , the duct  30  including a venturi constriction  34 . The bottle or jar  20  contains a concentrate containing a foaming agent; and a duct  36  extends from near the bottom of the bottle or jar  20  to the duct  30  at the venturi constriction  34 . Consequently the water flow along the duct  30  sucks the concentrate from the bottle or jar  20  into the water flow, so forming an aqueous solution which is sprayed out of the mist spray nozzle  32 . The mist spray nozzle  32  is within a conical mesh barrier  38 . The effect of the air flowing over the mist spray nozzle  32  and through the conical mesh barrier  38 , while the aqueous solution is sprayed from the spray nozzle  32 , is that foam fills the end of the open-ended tube  24  and flows down the open-topped chute  26 . 
     In addition, a pipe  40  leads from the solenoid-controlled valve  42  to the annular nozzle structure  25 . The solenoid-controlled valve  42  is controlled by a microprocessor or a timer (not shown) that may be within the cylindrical body  12 . The annular nozzle structure  25  is arranged to allow water to emerge as a blade or flat jet from the upper part of the annular nozzle structure  25  so as to impact on the lower part of the annular nozzle structure  25  and on the top end of the open-topped chute  26 . 
     In operation the end of the chute  26  is aimed at a weed  45 , near the base of the weed  45  (two weeds are indicated schematically in  FIG. 1 ) and the trigger  16  is pulled. This initiates operation of the air blower  14 , so as described above foam emerges from the open-ended tube  24  and flows down the open-topped chute  26  to cover the surfaces of the weed  45 ; the deposited foam  46  is indicated by a broken line in  FIG. 1 , and it will be appreciated that the foam  46  is partly on the ground around the weed  45  and partly on at least the lower parts of the weed  45 . After a predetermined time period set by the microprocessor or timer, the air blower  14  stops, so ceasing the supply of foam, and the timer operates the solenoid-controlled valve  42  so that the hot water from the flexible hose  22  flows through the pipe  40  to the annular nozzle structure  25 , so it sprays onto the upper surface of the open-topped chute  26 . The hot water consequently runs down the chute  26  and into the foam  46  covering the weed  45 . The hot water is therefore dispensed at the base of the weed  45 . Consequently the hot water comes into contact with the weed  45  within or beneath the foam  46 . This causes the tissues of the weed  45  to wilt and die; with a large weed the immediate effect is to kill the portion of the weed closest to the ground, and the remainder of the weed dies as a consequence. 
     In a modification the bottle or jar  20  may also include an electrical heater (not shown) to raise the temperature of the aqueous solution. This has the effect that the foam is formed at a temperature above ambient temperature, and so the foam  46  deposited on and around the weed  45  is above ambient temperature. When the hot water is then injected near the base of the weed, there is less loss of heat to the surrounding foam  46  and so more heat available for killing the weed  45 . 
     The foam  46  tends to stick to the surfaces of the weed  45 , as is desirable; but in addition it tends to stick to the surfaces of the open-topped chute  26 . Spraying the hot water through the annular nozzle structure  25  onto the upper surface of the open-topped chute  26  has been found to be effective at removing foam from these surfaces. 
     Referring now to  FIG. 3 , an alternative hand-held weed control apparatus  50  is shown in perspective, and partly cut away. The apparatus  50  comprises a generally cylindrical body  52  at one end of which is a protruding handle  55  which includes a trigger  56 . A multi-socket  54  projects below the handle  55 , having inlets  54   a ,  54   b  (see  FIG. 5 ) to which hoses carrying compressed air and pressurised hot water would be connected in operation. Mounted on the underside of the cylindrical body  52  is a bottle  57  which in use contains a concentrated solution of foaming agent. From the opposite end of the cylindrical body  52  projects an open-ended tube  58  of larger diameter (shown cut away), and an annular nozzle structure  60  may be provided at the open end of the tube  58 , from which projects an open-topped chute  62 . 
     Referring also to  FIG. 4 , an annular end fitting  64  of the cylindrical body  52  defines an external screw thread  65  whereby the tube  58  is connected to the cylindrical body  52 . A short tubular spider  66  attaches to the end of the annular end fitting  64  within the tube  58 , the spider  66  including legs to space it away from the end of the annular end fitting  64 , and the tubular spider  66  also defines an external screw thread. A foam-production vessel  68  locates concentrically within the tube  58 , being attached at its top end to the external screw thread of the tubular spider  66 , and being closed at its bottom end, so there is an annular gap between the outside of the foam-production vessel  68  and the inside of the tube  58 . (It will be appreciated that the tube  58  may instead be connected to the cylindrical body  52  using a different mechanism for example a snap fit; and that the foam-production vessel  68  may be attached to the tubular spider  66  using a different mechanism, for example a snap fit.) 
     The trigger  56  controls mechanical valves  70  (shown in  FIG. 5 ) within the protruding handle  55 , to control the flow of compressed air and pressurised hot water supplied through the inlets  54   a  and  54   b . Hot water is supplied to a tube  72  that includes a restriction or venturi (not shown), and the tube  72  projects through the tubular spider  66  into the foam-production vessel  68 . A tube  77  links the contents of the bottle  57  to the restriction or venturi in the tube  72 . The compressed air from the inlet  54   a  is supplied to a tube  76  that extends through the tubular spider  66  to near the bottom of the foam-production vessel  68 , and on the end of the tube  76  is mounted a porous stone block  78  (see  FIG. 4 ). 
     The hot water from the inlet  54   b  is supplied to a tube  80  that extends down into the open-ended tube  58 . The tube  80  may have an open end near the top of the tube  58 , as shown, the open end acting as a nozzle, or alternatively the tube  80  may feed the hot water into the annular nozzle structure  60 , if this is provided. 
     In operation, hot water from the inlet  54   c  is supplied through the tube  72 , so concentrate from the bottle  57  is sucked up into the hot water; the resulting solution of foaming agent is supplied to the foam-production vessel  68 . The compressed air passing along the tube  76  then passes through the pores of the stone block  78  to form multiple small bubbles, so that foam is continuously formed at the surface of the aqueous solution, the foam flowing up and through the tubular spider  66 , then flowing radially outwards between the legs of the tubular spider  66 , and then flowing down the annular gap between the foam-production vessel  68  and the tube  58 . Consequently the foam flows out of the open end of the tube  58  and flows down the open-topped chute  62 . 
     In use, therefore, the weed control apparatus  50  would be held with the end of the open-topped chute  62  near the base of the weed  45  (in the same way as shown in  FIG. 1 ), so as to enclose at least part of the weed  45  and the surrounding ground with foam  46 , as indicated by the broken line in  FIG. 1 . 
     When sufficient foam has been formed, foam production is ceased; and hot water is supplied through the tube  80 , so that the hot water then runs down the chute  62  and is injected through the foam  46  onto the base of the weed  45 . (Where an annular nozzle structure  60  is provided, the hot water is supplied through the tube  80  to the annular nozzle structure  60  and sprays out as a water blade on to the top of the open-topped chute  62  and then runs down the chute  62 .) This kills the weed  45  in the same manner as described above in relation to the weed control apparatus  10 . The spraying of the hot water onto the top of the open-topped chute  62 , as mentioned above, also washes off foam that might otherwise stick to the surface of the chute  62 . 
     In the weed control apparatus  50  the control of the timing of the two steps—foam production, and then hot water dispensing—uses a mechanical approach. Referring now to  FIG. 5 , this shows more details of the trigger  56 , and of the mechanical valves  70  associated with the inlets  54   a  and  54   b . The hot water supplied to the inlet  54   b  is supplied to two adjacent inlet ports  54   c  and  54   d . The inlet port  54   c  communicates through a valve  70  to the tube  72  for generating foam, while the inlet port  54   d  communicates through a valve  70  to the tube  80  for injecting hot water into the foam  46 . Each valve  70  includes a spring-loaded plunger  82  which is biased into the position in which valve  70  is closed; the plunger  82  associated with the hot water inlet  54   d  is shorter than the plungers  82  associated with the compressed air and hot water inlets  54   a  and  54   c.    
     The trigger  56  rotates about a pivot  84 , being biased by a spring  85  into the un-squeezed position, and is integral with a lever arm  86 ; the end of the lever arm  86 , as shown in  FIG. 6 , consists of two parallel prongs  87 , which act on the plungers  82  of the valves  70  connected to the tube  72  and the tube  76 . The underside of the lever arm  86  between the parallel prongs  87  acts on a rocker plate  88 . Referring again to  FIG. 5 , the rocker plate  88  can turn around a pivot  89 , its underside bearing against the spring-loaded plunger  82  associated with the tube  80 , and is biased by a spring  90  into a position in which the valve  70  is closed. An indicator plate  92  is integral with, and projects up from, the top of the rocker plate  88 ; the indicator plate  92  has an arcuate top surface which is adjacent to an aperture in the handle  55 , so the operator is provided with a visual indication of the status of the valves  70 . 
     Above the pivot  84  is a rotary damper  94  to retard clockwise rotation, which engages a rim of the trigger  56 . A rotary damper  98  to retard clockwise rotation is mounted so as to engage an edge of the indicator plate  92 . The rotary damper  98  provides more damping than the rotary damper  94 . 
     In operation, compressed air is supplied to the inlet  54   a , and hot water is supplied to the inlet  54   b , through hoses from external sources (not shown). When the operator squeezes the trigger  56 , the prongs  87  of the lever arm  86  push down on the plungers  82  that open the valves  70  connected to the tube  72  and to the tube  76 , so hot water flows via the inlet port  54   c  into the tube  72  and compressed air flows from the inlet  54   a  into the tube  76 , so producing foam as described above. The rotary damper  94  retards this rotation, to ensure foam is produced for a sufficient period. 
     Squeezing the trigger  56  even further pushes the rocker plate  88  down, and this opens the valve  70  connected to the hot water inlet  54   d , so hot water flows through the tube  80 . Hence hot water is injected as described above into the foam  46  on and around the weed  45 . When the operator releases the trigger  56 , the lever arm  86  and the trigger  56  rotate under the influence of the spring  85  back into their initial position, so the valves  70  connected to the tubes  72  and  76  close, and foam production ceases. At the same time, the rocker plate  88  is pushed back up by the spring on the valve  70  on which it acts, as well as by the spring  90 , but the upward motion of the rocker plate  88  is retarded by the rotary damper  98 . Hence the valve  70  connected to the tube  80  remains open for a period of time after the other valves  70  have closed. This ensures that hot water is dispensed for a sufficient period, and that hot water is dispensed after foam production ceases. 
     It will be appreciated that the weed control apparatuses  10  and  50  described above may be modified in various ways while remaining within the scope of the present invention, as defined by the claims. For example a different way of generating foam may be utilised; and for example the aqueous solution may be supplied in the required concentration, rather than being supplied as a concentrate to be diluted during operation.