Patent Publication Number: US-RE39636-E

Title: Agricultural methods with superheated steam

Description:
This is a continuation-in-part of Ser. No. 08/642,534, filed May 3, 1996 pending now U.S. Pat. No.  5 , 867 , 935 . 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to superheated steam for agricultural uses, and more particularly relates to delivering superheated steam in the field in fumigating, weeding, defoliating, and drying applications where the superheated steam is selectively delivered above and/or below the soil such as with a portable apparatus. 
     BACKGROUND OF THE INVENTION 
     Selective defoliation of a field growing crop such as grape vines has long been known as a desirable practice. Thus, for example, U.S. Pat. 2,865,135, issued Dec. 23, 1958, inventors Gamboni et al. discloses a grape leaf stripping mechanism to strip the leaves from grape vines by a mechanical apparatus rather than manual defoliation. The apparatus disclosed by this patent uses a pair of heaters to effect the defoliation. 
     More recently, the University of California publication on Grape Pest Management (2nd Edition, 1992, publication 3343) notes that among the practices for disease control are the removal of basal leaves from vines approximately two weeks after bloom. This practice reduces Botrytis bunch rot and produces a superior wins grape in many North Coast vineyards, and has also been reported to reduce first-generation leaf hoppers. The publication notes that most leaf removal is presently done by hand, but that mechanical systems are being developed and used by several growers. (Supra, xi.) 
     Removal of basal leaves on grape vines also permits the grape clusters to hang free and allows light penetration for coloring and budwood development, and allows air and chemical spray penetration for reducing molds, moisture, and insect infestation. Leaf removal has proven to produce a better acid/sugar ratio in ripening berries, and thus results in better quality wines and/or juices. 
     Manual defoliation is, obviously, labor intensive and thus tends to be costly. In addition, manual defoliation when performed shortly after fruiting tends to bruise the very small berries in the fruit cluster. Further, manual defoliation leads supply to displace pests such as leaf hoppers to the adjacent, remaining leaves where they can continue to wreak their damage and subsequently can return to the fruit cluster. 
     The presently known mechanical means for defoliating are disadvantageous because those that blow air or pull a vacuum tend to damage the berries by bruising or removing the berries themselves. 
     Another problem area for cultivated fields and crop maintenance such as vineyards particularly in California are that typical soils contain nematodes that feed on roots, which reduce root efficiency. Nematode infestation of vineyards are manifested by reduced vigor and yield with a light yellowing of leaves because nematode-infected vine roots are unable to meet above-ground demands for nutrients and water. 
     Preplant fumigants such as methyl bromide profoundly affect nematodes, and current advice for preparing a new vineyard includes the application of a nematicide such as methyl bromide (Grape Pest Management, supra, p. 290). However, methyl bromide bas been implicated in harming the ozone layer. As a consequence, considerable environmental pressure has been building against its use. Nevertheless, in February 1996, the California Senate voted to delay a proposed ban on the ozone-depleting fumigant, methyl bromide, until the end of 1997. A reason for delaying the proposed ban was due to lack of effective alternatives for agriculture in soil pest control, particularly for crops such as strawberries. 
     On small scale soil treatments, nurseries have been able to use steam as a sterilant for minimizing fungal infections. Thus, bedding plant nurseries have been able to grow seedlings in steam sterilized soils. But such small scale soil treatments are not presently practical or possible for in the field use. Further the steam used is not a very efficient process, since it involves for example, temperatures close to 212° F. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a superheated steam delivering apparatus useful in practicing aspects of the invention; 
         FIG. 2  shows a block diagram of the superheated steam delivery portion of the superheated steam delivery apparatus; 
         FIG. 3  shows a cross-sectional view of a steam generator; 
         FIG. 4  shows a cross-sectional view of a steam separator; 
         FIG. 5  shows a top view of the steam separator shown in  FIG. 4 ; 
       FIG.  6 . shows a cross-sectional view of a superheated steam generator and control system; 
         FIG. 7  shows a cross-sectional view of a nozzle as a means for distributing superheated steam as embodied in the invention; and 
         FIG. 8  shows a perspective view of knives as another means for distributing superheated steam as embodied in the invention. 
     
    
    
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide in the field agricultural uses of superheated steam that may be selectively delivered for applications such as fumigation, weeding, defoliation, and drying. These objects are achievable through use of a portable apparatus capable of delivering superheated steam at selected locations to plants or soil in agricultural fields. Superheated steam may be delivered to trellised plants, such as, for example, grapes and berries, while delivery to soil is useful, for example, for a wide variety of plant cultures, including strawberry fields and vineyards. 
     In one aspect of the present invention, an agricultural method for in the field use comprises the selective delivery of sufficient superheated steam to soil in a field to kill undesired organisms. The undesired organisms can be insects, whether in adult or larval form, and worms, such as nematodes. The undesired organisms can also be weeds. The superheated steam is preferably delivered at a temperature above about 250° F., and can be delivered adjacent to the soil surface (above ground) or can be by penetrating the soil to deliver the superheated steam therein. 
     In another aspect of the present invention, a method for defoliating plants, preferably grape vines, is provided whereby superheated steam is delivered to basal leaves. When treating grape vines, the superheated steam is preferably delivered adjacent to developing grape berries within a desired volume, or envelope. The desired envelope has a characteristic dimensional size within which the treating steam has a temperature range sufficient for defoliation, but which surprisingly does not damage the grape berries themselves. 
     In yet another aspect of the present invention, a method for treating raisin grapes or prune plums is provided to decrease time of drying on the cane or tree prior to harvest. 
     Other objects and advantages of the invention will become apparent upon reading the detailed description and as set out in the appended claims. 
     Detailed Description of the Preferred Embodiment 
     Broadly, the invention involves the selective delivery of superheated steam for a variety of agricultural applications. This selective delivery of superheated steam has been made possible by a particularly preferred apparatus, which will the illustrated as the best mode contemplated for carrying out the present invention; however, other apparatus capable of generating superheated steam may be used so long as the superheated steam is delivered at the temperature or temperature ranges necessary for practicing aspects of the invention. 
     The preferred apparatus for use in practicing the invention includes a portable frame, a water reservoir mounted on the frame and defining an upstream end of a fluid passageway carried by the frame, a first chamber disposed along the fluid passageway downstream of the reservoir, which includes, a beater operable to convert water being flowed from the reservoir and through the chamber into steam, a second chamber disposed along the, fluid passageway and of a construction sufficient to receive steam at a first temperature range downstream of the first chamber and to heat the received steam to within a second (elevated) temperature range so that steam is superheated, and an outlet adapted to deliver a flow of superheated steam from the second chamber. 
     One particularly preferred application in accordance with the invention is to defoliate ;grape vines. Because the heat of superheat can be generally transformed into work without forming moisture, the use of superheated steam efficiently permits application of high temperature but relatively low velocity flows in the vicinity desired for such application, such as adjacent to developing grape berries without bruising or damaging the berries themselves, yet while accomplishing efficient defoliation. By contrast, were one to use steam that was not superheated, then the developing berries would be subjected to bruising and other damage. Further, normal (wet) steam cools rapidly so that were one to try to direct wet (not superheated) steam towards foliage, little or no leaf removal would be achieved. 
     The preferred apparatus for superheated steam delivery has a portable frame that is of sufficiently small dimensions and not overly heavy so as headily to be moved over a field of growing plants (where the agricultural application is to deliver superheated steam adjacent to leaves of above-ground plants, for example). Present day vineyards on the west coast of the United States typically grow grape vines on trellises (e.g. cordon trained grapes). Vine rows are frequently spaced about 8-12 feet apart in the United States (and more narrowly in Europe). Grape growers pull various apparatus down the vine roves by tractor during the growing season and at harvest. Thus, a preferred apparatus embodiment typically has the frame width designed to fit vineyard rows down to about 8 feet wide, which are analogous to the dimensions of frames used for grape gondolas and machine grape harvesters 
     Preferred embodiments of the invention include a rail, or ski, extending from the frame and adjustably moveable against field growing plants in a manner analogous to a horizontal picking rail of grape harvester truck shakers, which move along the trellis and address the trunk and grape stakes below the cordon height level. A defoliation embodiment of the invention will first be described, followed by a description of some alternative embodiments, useful as for treating soft in accordance with the invention. 
       FIG. 1  illustrates a superheated steam delivery apparatus  10  as embodied in the invention being used, for example, to defoliate a vine  2 , tree, shrub or the like. The apparatus  10  generally comprises a superheated steam delivery portion  12  mounted on a hitch or portable frame  14 , wherein said frame engages the ground through wheels  16  or by other similar means such as track type treads. The frame  14  can be hitched with a tractor (not shown), for example, to move the superheated steam delivery portion along a row of foliage for superheated steam treatment purposes. Although as shown the superheated steam delivery portion  12  is mounted on a trailer, it shall be understood that such portion can be an integral part of a tractor, truck or moving vehicle. The portable frame  14  may also include a rail, or ski, (not illustrated) extending from the frame which can be adjustably moved against the field growing plants  2  of a construction and in a manner analogous to that known for the rails of grape harvesters. 
     The superheated steam delivery portion  12  of the apparatus  10  includes a means for selectively distributing superheated steam to a desired location, such as nozzle  20  which has a pattern of orifices through which the superheated steam is distributed and thus delivered to a particular plant for which treatment is desired. The nozzle is generally held a selected distance from the foliage  2  such that the foliage is exposed to the flow of the superheated stream. The characteristics of the superheated steam are important if optimum defoliation is desired while damage to the berries or other fruit avoided, but optimum characteristics of the superheated steam will vary and depend on the type of plant and the time of leaf growth to which treatment is being applied. 
     For example, if defoliation of grapevines is desired soon after berries are forming while the adjacent leaves are young and thus tender, it is preferable that the superheated steam flowing outwardly from the nozzle be delivered approximately 12 to 15 inches in height and within a temperature range of 250° F. to 500° F. at such height but at a flow less than 60 psi. This requires that the temperature of superheated steam be raised in the second chamber (a superheating steam generator) to higher than the 250° F. to 500° F. range of actual delivery. In order that the selective delivery of superheated steam to the desired location be at this range, the superheated steam emerging from the superheated steam generator  28  should be at a temperature of at least about 300° F., typically in a temperature range of from about 300° F. to about 800° F., and at a pressure range of about 5 PSI to about 60 PSI. 
     This technique of applying a flow of superheated steam having desired characteristics to a field of grapevines has many benefits. For instance, defoliating of basal leaves allows grape dusters to hang free so that developing fruits are free of wind damage and the bloom is not rubbed away. Leaf removal also allows more light penetration for coloring and budwood development. Leaf removal further facilitates penetration of air and chemical spray for reducing molds, moisture and insect infestation. Moreover, defoliating of leaves has resulted in producing better acid/sugar ration in ripening berries, thus resulting in better quality wines and juices. 
     Although the lust described apparatus is particularly useful for defoliation of basal leaves on grape vines, it can readily be used to direct superheated steam adjacent to the area where root stock has been grafted to the desired grape variety. Stray suckers or canes sometimes tend to grow from the root stock below the graft point, and the inventive apparatus can be used to remove these undesirable suckers by application of the superheated steam. The number, size and shape of distributing orifices in nozzle  20  thus will vary for such different uses. 
     Other applications include applying the superheated steam to the soil surface to kill undesired organisms such as weeds and to the upper layers of soil as it is turned over to fumigate the soil. In this application, the nozzle  20  will preferably be replaced by one or a plurality of tines, or knives in which orifices may be vertically aligned for superheated steam distribution. Particularly in the latter (or latter two) applications, one can admix another soil or weed treatment agent with the superheated steam, since many insecticides, fumigants, and the like are already applied in vapor form and thus can be combined, such as entrained, with the flow of superheated steam. 
       FIG. 2  represents a block diagram of the superheated steam delivery portion  12  of the superheated steam delivery apparatus  10 . The superheated steam delivery portion  12  generally comprises a water reservoir  22 , a steam generator  24 , a steam separator  26 , a superheated steam generator  28  and nozzle  20 . The superheated steam delivery portion  12  also includes an electrical power supply  30  and a fuel tank  32  for supplying the necessary power to run the various components of the superheated steam delivery portion  12 . 
     The superheated steam generating process begins at the water reservoir  22  which holds the water supply necessary to generate the: required quantity of superheated steam for treating the foliage  2 . The water reservoir should have a capacity to produce sufficient superheated stream so that a desired portion of a field of plants is superheated steam treated while maintaining portability. In a preferred embodiment, for example, the water reservoir  22  has the capacity to hold 300 gallons of water, which permits treatment of about 1-4 acres per hour when the apparatus is moved at a rate of about 1-2 miles per hour through rows about 12 feet wide. 
     In the first step of the superheated steam generating, process, water along line  34  is pumped into the steam generator  24  so that a sufficient amount of steam is produced at the output of the steam generator  24  The rate of flow of water from the water reservoir  22  to the steam generator  24  should be sufficient in order for the steam generator  24  to continuously produce steam at its output without coming to a dry state. In the preferred embodiment, for example, water from the water reservoir  22  is pumped at about a rate of 45 gallons per hour (gph) to the steam generator  24 . This rate results in the steam generator  24  continuously converting about 33 gph out of the 45 gph of water into steam. Of the 12 gph surplus water, about 11 gph is recycled back to the water reservoir  22  along line  36  so that an efficient use of water results. 
     As will be discussed more in detail later, the steam generator  24  performs a heat exchange process upon the incoming water so that steam is generated at its output. Briefly, the steam generator  24  receives fuel from the fuel tank along line  40  and combusts it with pressurized air to form a hot gas, mixture. The steam generator  24  also receives electrical power from the power supply  30  along line  38  in order to run an air blower. The air blower forces the hot gas mixture to flow within the steam generator thus exposing the water therein to the heat from the continuously flowing hot gas mixture. As a result, steam is generated at the output of the steam generator. In the preferred embodiment, steam at the superheated steam generator output is at a temperature of about 300° F. to 700° F. (or higher) and at a pressure of about 5 to 60 PSI. 
     Although in the preferred embodiment the vapor produced at the output of the steam generator  24  is at a relatively high temperature, typically about 80 percent of it is steam and about 20 percent is water droplets by weight. It is preferred to remove most of the water droplets before the vapor undergoes a superheating steam process. Hence, the vapor from the steam generator output is fed to the steam separator  26  along line  42 . Water droplet removal is preferred because one can more efficiently heat the steam without using energy to vaporize the water droplets. Although removal of the water droplets from the vapor flowing from the steam generator  24  is preferred, it shall be understood that such removal is not necessary and that the vapor from the steam generator can be directly fed into the superheated steam generator  28 . As will be explained in more detail later, the steam separator  26  preferably uses a centrifugal and condensation process to remove most, if not all, of the water droplets from the vapor flowing from the steam generator  24  which results in a high quality saturated steam vapor at the steam separator output. Most of the water droplets removed from the vapor is recycled back to the water reservoir  22  along line  36  so that an efficient use of the water supply is achieved. 
     The steam at the output of the steam separator  36  is thereafter fed to the superheated steam generator  28  along line  44  so that superheated steam is produced at the output thereof. The superheated steam generator performs essentially the same heat exchange process as the steam generator  24  does, but typically on a smaller scale. Briefly, the superheated steam generator receives fuel from the fuel tank  32  along line  46  and combines it with air to form a hot gas mixture. The superheated steam generator  28  also receives electrical power from the power supply  30  along line  48  to run an air blower. The air blower forces the hot gas mixture to flow within the superheated steam generator so that the low moisture (dry) steam therein is exposed to the heat of the continuously flowing hot gas mixture. As a result, superheated steam is produced at the output of the superheated steam generator  28 . Thus, in the preferred embodiment, the superheated steam at the outlet of the superheated steam generator  28  is at a temperature of about 800° F. and at a pressure of about 50 PSI. 
     The superheated steam at the output of the superheated steam generator is subsequently fed to the nozzle  20  along line  50  so that the superheated steam can be selectively applied to the plant for treatment. The nozzle receives the superheated steam from the superheated steam generator  20  and directs, or distributes, it such that the flowing superheated steam from the orifices of the nozzle  20  has a desired envelope shape. As will be understood, actual patterns of distribution and nozzle sizes and shapes will vary depending upon the desired applications. In a preferred embodiment for vine defoliation, the superheated steam flowing outwardly from the outlet nozzle  20  may provide a vertical or horizontal envelope of approximately 12 to 15 inches in height and within a temperature range of about 250° F. to 500° F. at such height. It has been found that such characteristics obtain optimum defoliation of grapevines, at least in the vineyards located in the Northern part of California. It shall be understood that the optimum envelope and characteristics of the outwardly flowing superheated steam will depend on the particular type of foliage being treated. 
     Referring now to  FIG. 3 , a cross-sectional view of the steam generator  24  is shown. The steam generator  24  generally operates as a heat exchanger whereupon incoming water from the water reservoir  22  is continuously exposed to the heat of a hot gas mixture flow to convert the water into steam. The steam generator  24  can generally be divided into three portions: a burner portico  52 , a heat exchanging portion  54  and an exhaust portion  56 . A cylindrical metal housing  58 , preferably made from a heavy gauge corrosion resistant aluminized steel and having a side wall  59 a, a top wall  59 b and a bottom wall  59 c, encases the heat exchanging portion  54  and the exhaust portion  56 . The burner portion  52  sits over the top wall  59 b of the metal housing  58 . The steam generator  24  further includes an external pump  60  for pumping in water from the water reservoir  22  which is delivered along; flowline  34  and also includes an electric motor  62  for driving the pump  60  and for driving a component of the burner  52 . Preferably, the pump  60  is a positive displacement multi-cylinder pump. 
     The burner portion  52  is the portion of the steam generator  24  which produces the hot gas mixture needed for the heat exchanging process. It generally comprises an air blower  64 , a fuel inlet pipe:  66 , a burner head  68  and an elongated fire tube  70 . The air blower  64  is coupled to the electric motor  62  by way of a drive train (not shown) and drives the blower such that pressurized air  72  is forced downward towards the fire tube  70 . The fuel inlet pipe  66  is coupled to a valve  62  which selectively allows fuel to flow from flowline  40  towards the burner head  68  byway of the fuel inlet pipe  66 . The burner head  68 , which is situated within the elongated fire tube  70 , ignites the flowing fuel using the pressurized air  72  to form a downward-flowing, hot gas mixture  74 . The hot gas mixture  74  is forced downward into the elongated fire tube  70  for complete combustion. The elongated fire tube  74  extends coaxially into the metal housing  58  by way of an aperture in the top wall  59 b. 
     The heat exchanging portion  54  is the portion of the steam generator  24  where most, if not all, of the heat exchanging process occurs. The heat exchanging portion  54  generally comprises a pair of concentric spirally wound pipes, i.e. an outer spirally wound pipe  76  and an inner spirally wound pipe  78 . Preferably, the pipes are ¼ inch IPS schedule  80  pipes. The outer spirally wound pipe  76  preferably comprises 85 feet of pipe and measures 14 inches in outside diameter and 35 inches in length after coiling. The inner spirally wound pipe  78  preferably comprises 45 feet of pipe and measures 11 inches in outside diameter and 18 inches in length after coiling. The outer and inner pipes  76  and  78  are joined at the bottom of the heat exchanging portion  54 , and in the preferred embodiment, the outer and inner wound pipes form a continuous single pipe that has been serpentined to form the outer and inner spirally wound pipes  76  and  78 , and has a total length of 1.30 linear feet. 
     The heat exchanging portion  54  further includes outer, top and bottom ceramic refractorics  56 a- 56 c which generally encase the outer and inner spirally wound pipes  76  and  78  and insulates the heat exchanging portion  54  from cooler ambient temperatures. The outer ceramic refractory  56 a is cylindrical in shape, concentric with the outer and inner spirally wound pipes and snugly covers the outer surface of the outer spirally wound pipe  76 . The outer ceramic refractory&#39;s cylindrical shape is preferably smaller in diameter and in height than the metal housing  58 , and is mounted generally near the upper portion of the housing and tangentially along a portion of the inner surface of the side wall  59 a. The top ceramic refractory  56 b is a circular disk in shape with a centrally located aperture extending therethrough and situated between the top coil of the outer spirally wound pipe  76  and the top wall  59 b of the metal housing  58 . The aperture of the top ceramic refractory is generally concentric with the aperture of the top wall  59 b, wherein the fire tube  70  extends therethrough. The bottom ceramic refractory  56 c is generally a circular disk in shape and is joined to the bottom two coils of the inner spirally wound pipe  78 , thus sealing off the lower end of the inner coil  78 . Such a construction results in three heat exchanging compartments within the heat exchanging portion  54 : a lower compartment  80  defined by the cylindrical space within the inner spirally wound pipe  78  and sealed at the lower end by the bottom ceramic refractory  56 c; an upper compartment  82  defined as the space between the upper spirally wound pipe  76  and the fire tube  70  and extending from the top ceramic refractory  56 b to the top of the inner spirally wound pipe  78 ; and a corridor compartment  84  defined as the space between the outer and inner spirally wound pipes  76  and  78 . 
     The outer spirally wound pipe  64  is fluidly coupled to the pump  60  at the top coil thereof, whereby water from the water reservoir  22  is pumped into the steam generator  24  initially into the outer spirally wound pipe  78 . The outer spirally wound pipe  64  is also fluidly coupled to the inner spirally wound pipe  78  at the bottom coil of both pipes  76  and  78 . An outlet pipe  86  is fluidly coupled to the inner spirally wound pipe  78  at the top coil thereof and extends downward within the lower compartment  80  through an aperture within the lower ceramic refractory  56 c and radially outward within the exhaust portion  56  and exits the metal housing  58  through an aperture into flowline  42 . In the preferred embodiment, the outlet pipe  86  is also part of the continuous wound pipe that makes up the outer and inner spirally wound pipes  76  and  78 . 
     The exhaust portion  56  of the steam generator  24  is generally a duct for allowing the cooled hot gas mixture  74  exiting the heat exchanging portion  54  to flow out of the steam generator  54  to the atmosphere. The exhaust portion  56  generally comprises the space between the heat exchanging portion  54  and the bottom and side walls  59 c and  59 b of the metal housing  58 . Thus, exhaust gas flowing out of the bottom of the heat exchanging portion  54  flows into the exhaust portion in the space between the heat exchanging portion  54  and the bottom wall  59 c of the metal housing  58 , and then subsequently flows upwardly in the space between the heat exchanging portion  54  and the side wall  59 a of the metal housing  58 . The exhaust gas mixture  74  thereafter exits the steam generator  24  through aperture  88  at the top wall  59 b of the metal housing  58 . 
     In operation, the steam generator&#39;s pump  60  continuously delivers water from the water reservoir  22  into the steam generator  54  initially by way of the outer spirally wound pipe  76 . At the same time, fuel is delivered to the burner head  68  from the fuel tank  32  by way of flowline  40 , valve  62  and fuel inlet line  66 . The burner head  68  ignites the fuel using the pressurized air  72  from the air blower  64  and forms a downward-flowing hot gas mixture  74 . Combustion of the hot gas mixture  74  occurs while the gas  74  is flowing downward through the fire tube  70 . The hot gas mixture  74  subsequently exits the fire tube  70  and flows into the heat exchanging portion  54 ; and specifically, flows initially into the inner compartment  80 , wherein heat from the hot gas mixture  74  exchanges with the fluid flowing through the inner spirally wound pipe  78 . The flowing hot gas mixture  74  thereafter encounters the lower ceramic refractory  56 c and changes direction flowing upwardly into the upper compartment  82 , wherein heat from the hot gas mixture  74  exchanges with the fluid flowing through the outer spirally wound pipe  76 . The flowing hot gas mixture  74  next encounters the upper ceramic refractory  56 b and changes direction flowing downward towards the corridor compartment  84 , wherein the heat from the hot gas mixture  74  exchanges with the fluid flouring through the outer and inner spirally wound pipes  76  and  78 . Thereafter, the flowing hot gas mixture  74  flows out of the heat exchanging portion at the lower end of the corridor compartment  84  and into the exhaust portion  56  of the steam generator  24 , whereby the gas mixture subsequently exits the steam generator  24  as waste. 
     The steam generator  24  is enclosed so that the hot gas mixture  74  is under pressure and forced at relatively high velocity past the pipe coil surface, therefore maximizing the heat exchanging process. Of the 35.75 square feet of coiled pipe surface in the complete coil, only 24 square feet of pipe surface provides the actual heat exchange. The remaining 11.75 feet of surface are on the outside of the outer spirally wound pipe and are not in contact with the hot gas mixture. As a result, the heat exchange process typically delivers a vapor to the flowline comprising of 80 percent steam and 20 percent water droplets by weight. 
       FIGS. 4 and 5  illustrate a steam separator  26  for removing the undesired water droplets and for delivering steam substantially free of unvaporizcd water to the superheated steam generator  28 . The steam separator  26  preferably operates to remove the water droplets from the vapor produced by the steam generator  24  by a centrifugal separating method. Thus, the steam generator  26  may comprise a metal housing  122  having a top wall  124 a, a side wall  124 b and a bottom wall  124 c, and whose boundaries define a chamber  128  within the metal housing  122 . The top wall  124 a has a centrally located aperture  114  and a cylindrical outlet stack  124  extending vertically and outwardly therefrom and being concentric with the aperture  114 . A vertical insulated separating cylinder  110  having; an opened top and bottom is mounted to the inner surface of the top wall  124 a and preferably situated such that its longitudinal axis is coaxial with that of the outlet stack  126 . 
     The steam separator  26 , further has an inlet tube  112  extending outwardly from the metal housing  122  to flowline  42 , wherein steam from the steam generator  24  is brought into the steam separator  26  by way of flowline  24  and inlet tube  112 . The inlet tube  112  also extends inward into the chamber  128  and tangential to the side wall of the separating cylinder  110 . Located near the bottom of the chamber  128  is a drain pipe  116  extending radially outward from the side wall  124 b of the metal housing  122 . The steam separator  26  further includes an external condensate trap  120  which is fluidly coupled to the chamber  128  by way of dip tube  118 . The dip tube  118  extends vertically upward within the chamber lab from about  3  inches above the bottom wall  124 c and then radially outward around the center of the chamber to the external condensate  120  by way of an aperture on the side wall  124 b of the metal housing  122 . 
     In operation, vapor and liquid from the steam generator  24  is delivered into the steam separator  26  by way of flowline  42  and inlet tube  112 . These vapor and water droplets circulate around the cylindrical separator  110 , whereupon the heavier droplets arc centrifugally separated from the steam to leave a high quality saturated steam. The saturated steam thereafter flows upwardly through the separating cylinder  110 , through the outlet stack  126  and exits the steam separator  26  into flowline  44 . 
     The superheated steam generator  28  is similar to the already described steam generator  24  in construction, but on a smaller scale. For example, a preferred embodiment apparatus has a total hourly heat release in a “steady state condition” (defined for the present purposes as superheated steam discharging from the superheated steam generator  28  at 800° F. while being supplied with about 240 lbs. of steam 50 PSI) of approximately 350,000 BTU/hour. Larger systems, of course are feasible. Of the 350,000 BTU/hour heat release, about 70% is provided by the steam generator  24  while about 30% is provided by the super-heated steam generator  28 . Both burners of the respective steam generator  24  and superheated steam generator  28  include conventional temperature controllers based on the steam output desired so that the steam flow is regulated to be continuous during use of the apparatus. For example, the superheated steam generator  28  preferably has a high firing rate so as to produce in short time intervals the elevated temperature required, yet to be able to quickly respond when the maximum temperature level of the process is reached. This may be achieved by the use of a bi-metallic sensing unit operating a pilot valve which in turn controls a modulating diaphragm gas valve on the fuel supply line so as to provide quick response and to control the outlet temperatures at about ±15° F. To achieve such quick response, the available heat input of the superheated is about 1.5 times the heat required to operate at the defined “steady state condition.” The thermostatic recontrolled pilot valve is preferably water-cooled by the feed water pump on the steam generator  24 , and is isolated from the elevated temperatures adjacent to it. The superheated burner system will not fire unless an adequate supply of steam is being fed into the superheated coil through a flow responsive control system, which responds to a differential pressure valve on the coil inlet and transmits this difference in pressure to a control which opens or closes the circuit to the fuel valve on the burner. 
     Turning to  FIG. 6 , a cross-sectional view of the super-heated steam generator  28  is shown in conjunction with a suitable superheated steam control system. In order for the superheated steam generator  28  to generate superheated steam at the “steady state condition,” fuel along flowline  46  is initially fed into a modulating control valve  132  by way of a controllable valve  130 . The modulating fuel valve  132  has a main fuel outlet coupled to flowline  133  which feeds fuel to the main burner of the superheated steam generator  28 . The modulating valve also has a secondary fuel outlet coupled to flowline  134  which allows fuel to flow to the burners pilot ignition system (not shown). Pilot fuel line  134  is coupled to a thermostatic recontrolled pilot valve  136  which is cooled by flowing cooling water in T-flowline  138 . The thermostatically controlled pilot valve  136  senses the temperature of the superheated steam exiting the superheated steam generator  28  and controls the modulating fuel valve  132  such that the superheated steam flowing out of the superheated steam generator  28  is maintained at “steady state condition” with a temperature variance of ±15° F. Such temperature can be verified by temperature indicator  140  which is situated within the path of flowline  50  at the superheated steam generator output. 
     With the modulating fuel valve  132  and the thermostatic recontrolled pilot valve  136  controlling the flow of fuel into the burner of the superheated steam generator  28  such that “steady state condition” is maintained, a continuous flow of saturated steam from the steam separator  26  is fed into the superheated steam generator  28  by way of flowline  44 , valve  42  and differential pressure valve  146 . The differential pressure valve  146  has an upstream and downstream outlet for sensing the pressure of the incoming saturated steam. Both the upstream and downstream outlets are coupled to a differential pressure responsive control  148  by way of flowlines  147 a and  147 b, respectively. Both flowlines  147 a and  147 b have water seal loops  149 a and  149 b to prevent any water droplets present in the saturated steam from flowing to the differential pressure responsive control  148 . The pressure of the incoming saturated steam is sensed by the differential pressure responsive control  148 , which in turn controls the controllable: valve  130  such that when the pressure of the incoming saturated steam is above a selected level the differential pressure responsive control  148  opens the controllable valve to allow fuel to flow to the modulating valve  132 . On the other hand, when the pressure of the incoming saturated steam is less than the selected level, the differential pressure responsive control  148  shuts the controllable valve  130  so that fuel is prevented from flowing into modulating valve  132 . Thus, only when the pressure of the incoming saturated steam is above the selected level, will the superheated steam generator  28  be operable. 
     Once the superheated steam exits the superheated steam generator  28 , it flows into the nozzle  20  by way of flowline  50 . The superheated steam so delivered typically will consist essentially of water vapor and air (e.g. is without combustion gases generated from the burner). However, insecticides, fumigants, drying aids, or the like can be combined with, or entrained in, the flow of superheated steam so as to efficiently treat the desired soil or organism in one operation. Thus, agents to be entrained in the flow of superheated steam will typically be injected into flowline  50  after exiting; the steam generator  28 . 
     The nozzle  20  is designed so that the superheated steam flowing out of the nozzle  20  provides for equal distribution of the discharged steam across the height of the nozzle exit and at a velocity sufficient to carry the superheated steam out to the desired distance and desired temperature without undue infusion of cooling ambient air. The temperature of the discharge from the superheated can be varied to elevate or lower the superheated stream temperature conditions and still achieve the desired temperature at the desired distance. 
     Referring to  FIG. 7 , a cross-sectional view of the nozzle  20  is shown. The nozzle  20  comprises an inlet tube  150  for allowing superheated stream to flow into the outlet nozzle  20  from flowline  50 . The outlet nozzle  20  further has a housing  152  having walls defining a space within which has been partitioned into four separate chambers by a manifold  154  and a pair of perforated baffles  156  and  158 . 
     In operation, superheated steam enters the nozzle  20  into the first chamber  160  by way of the inlet tube  150 . The first chamber  160  is defined as the space bounded by the walls of the housing  152  and the manifold  154 . The manifold  154  has a series of orifices  168 , preferably equally spaced along the manifold, to allow equal distribution of superheated steam to flow from the fiat chamber  160  to the second chamber  162 . 
     The second chamber  162  is defined as the space bounded by the manifold  154 , the housing  152  and the first perforated baffle  156 . Superheated steam entering into the second chamber subsequently flows into the third chamber by way of perforations  170  on the first perforated baffle  156 . The perforations  170  on the first perforated baffle  156  are preferably spaced throughout the entire surface of the first perforated baffle  156  to allow equal distribution of superheated stream to flow into the third chamber. 
     The third chamber  164  is defined as the space bounded by the first perforated baffle  156 , the housing  152  and the second perforated baffle  158 . Perforation  172  on the second perforated baffle  158  are similar to that of the first separated baffle  156  so to allow equal distribution of superheated steam to flow into the exiting chamber  166 . 
     The exiting chamber is defined as the space bounded by the second perforated baffle  158  and the housing  152 , and has an opening  174  at one end where superheated steam flows out of the nozzle  20  where it is applied to the desired foliage  2 . The sizes of the orifices  168 , the perforations  170  and  172 , and the opening  174  allow for the desired BTU release, temperature and velocity of the treating superheated steam. 
     In defoliation applications of the superheated steam delivery apparatus  10  for grape vines, the nozzle  20  preferably tracks on the vine  2  in such a way that the superheated steam of approximately 250° F. to 500° F. envelopes the vine  2  at the desired distance. Thus, it is desirable to connect the nozzle  20  so that it can easily move in and out to track the vine  2  at the desired distance from the vine. Therefore, in a preferred embodiment, all connecting lines of the superheated steam delivery apparatus  10  are flexible; this includes the water lines  34  and  36 , the steam lines  42 ,  44  and  50 , the power lines  38  and  48 , and the fuel fines  40  and  46 . 
     So that the nozzle  20  may be easily positioned for treating the foliage  2 , the use of hydraulic sensing or mechanical sensing to move the nozzle in and out can be employed. For example, a parallel link arm assembly holding a ski along the vine trunk to correctly position the nozzle can be used. Such an assembly is known to the art in connection with grape harvesters. 
     Returning to  FIG. 1 , the nozzle  20  is illustrated for selectively delivery of superheated steam above the soil, such as adjacent to leaves of above-ground plants; however, as already described, superheated steam can be used to kill undesired organisms such as weeds on the surface of the soil or undesirable nematodes within the soil. When killing weeds above ground, one can position nozzle  20  several inches above the soil surface and permit the superheated steam to be delivered adjacent to the soil surface. Post-emergent weed control in accordance with the invention has experimentally demonstrated with such recalcitrant weeds as Bermuda grass and morning glory. Surface rhizomes and seeds of these weeds were also killed or their ability to grow retarded. 
     Turning to  FIG. 8  where the inventive apparatus is used to kill insects or their larvae within soil, then the apparatus can include another means for distributing superheated steam, such as a plurality of knives  200  mounted on a bar  202  and spaced from each other, such as by a four inch spacing. Bar  202  as illustrated may be a standard A-frame toolbar conventionally known and used with apparatus such as a cultivator and fertilizer side dressing sled. These knives can be drawn through soil to a depth, for example, of about 24 inches, while emitting superheated steam delivered through a tube to orifices (not illustrated) along one side of the knives. More shallow injections than a depth of 24 inches, of course, may be found suitable, and the spacing between the knives may be adjusted as desired. For example, strawberry beds would typically only need soil penetration and superheated steam injection in a range of about two inches to about ten inches, although for fumigating applications in general one may wish to penetrate the soil and inject superheated steam in a range of about 2 inches to about 20 inches. 
     By increasing the temperature at which the superheated steam is selectively delivered to in the field plants, one can also increase efficiency for fruits intended to dry (or partially dry) in the field before harvest, e.g. prune plums and raisin grapes. For example, by contrast to use of superheated steam in grape vine defoliation where damage to the young grape berries must be avoided, one can selectively deliver higher temperature superheated steam, usually more slowly, to raisin grapes to assist them in drying. In such a drying application, one preferably entrains a drying aid (such as methyl or ethyl oleate) in the flow of superheated steamy which assists in moisture evaporation across the usual waxy barrier on the fruit&#39;s skin. 
     Aspects of the invention will now be illustrated by the following examples which are intended to illustrate but not limit the invention. 
     EXAMPLE 1 
     A prototype of the superheated steam apparatus as described for grape defoliation was pulled by a tractor moving about 1-2 miles per hour through grape vine rows spaced 12 feet apart. With a 300 gallon water reservoir, superheated steam was applied to about 1-2 acres per hour. Within minutes of application, the treated leaves shriveled. The leaves were dry within an hour, followed by leave drop over the next several days. Further, leave hoppers on those directly treated leaves and adjacent leaves were killed and observed to have fallen from the growing vines; however, the developing grape berries were not harmed at all. 
     EXAMPLE 2 
     The top four inches of a worked soil bed had superheated steam applied. Samples of the soil were then inspected and were shown to be substantially sterilized. 
     EXAMPLE 3 
     The prototype of the superheated steam apparatus had the steam nozzle :placed facing down to the row berm of orchard and vineyard rows at a distance 2 inches to 3 inches above the ground and was moved parallel to the ground at between ¼ mph and 1½ mph, depending upon the amount of vegetation to be killed. The superheated steam that was so delivered was in a temperature range of 500° F.-700° F. which was effective to kill the growing weeds and to keep most of the weed seeds that had dropped from germinating. 
     EXAMPLE 4 
     Methyl oleate and ethyl oleate are known and used to assist in speeding moisture evaporation through the waxy film that naturally occurs on the skin of fruits such as raisin grapes and prune plums. In an application of superheated steam for grape defoliation as described by Example 1, an additional operation was simultaneously performed by injecting Methyl oleate or ethyl oleate into the flowline  50  before the superheated steam flowed into nozzle  20 . In this instance, the prototype had dual nozzles and a flow divisional valve controlled the superheated steam flow to the, right or left nozzle. The superheated steam, which included methyl- or ethyl oleate, was thus applied to raisin grapes in conjunction to removal prior to harvest. This permitted more rapid moisture evaporation through the grape skin surfaces. 
     It is to be understood that while the invention has been described above in conjunction with preferred specific embodiments, the description and examples are intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims.