PLANT DISEASE TREATMENT

Abstract: The present invention relates to an apparatus (1) suitable for use in the treatment of tubers (22) comprising a vessel (2) having an endless conveyor means (3) for conveying said tubers (22) through a water holding zone (10) between a loading station (23) and a discharge station (27). Water heading and circulation means (28, 29) are provided for heading and circulating the water at a temperature from 50 to 65°C. A conveyor drive control means (20, 32) is provided for controlling the speed of said conveyor means (3) so as to determine the transit time between said loading and dis­ charge stations (23,27) thereby determining the tuber resi­ dence time in said water holding zone 10. The conveyor means (3) has tuber support and retaining means (14-19) of generally open-work structural form so as to permit water flow therethrough to substantially all sides of said tubers (22), said conveyor means (3) being further formed and arranged so as to tumble and/or roll said tubers (22) at least along a substantial part of said conveyor path portion. The invention also provides a method of treatment of potato blackleg in tubers (22) comprising the steps of size-grading the tubers (22), bringing them to a thermal treatment zone (10), introducing them into a body of thermal treatment fluid at a temperature of 50 to 65°C for a period of time sufficient to substantially kill the blackleg organism without signifi­ cantly damaging the tuber tissue, and cooling the tubers (22).

Description: PLANT DISEASE TREATMENT The present invention relates to the treatment of plant diseases and in particular to the treatment of temperature sensitive diseases such as blackleg and softrot (caused by Erwinia Spp.)in potato tubers and other diseases in likeplantinatter. The thermal treatment of tubers involves considerable problems due to the difficulty of effectively killing all or at least most of the disease organism infecting the tuber without at the same time significantly injuring the tuber tissue which is an important consideration where subsequent long-term storage of the tubers is required and even more important where the tubers are required for seed purposes. It is an object of the present invention to avoid or minimize one or more of the above problems and in particular to provide effective and economic methods and means of treating such diseases in tubers and like vegetable matter. The present invention provides a method of treatment of potato blackleg in potato tubers comprising the steps of: grading potato tubers according to size, preferably to within a size variation of 20% bringing size-graded potato tubers of a similar size, at a temperature at or below ambient temperature, preferably within the range from 4 to 300C 0 most preferably from 4 to 20 C, to a thermal treatment zone; ; introducing said tubers into a body of thermal treatment fluid having a thermal capacity substantially larger than that of said introduced tubers such that said introduced tubers have a substantially negligible effect on the temperature of said fluid which fluid is at a temperature of from 50 to 650C preferably from 50 to 560C, so as to substantially wholly surround the individual tubers with said fluid, and retaining said tubers in said fluid for a period of time sufficient to substantially kill the blackleg organism without significantly damaging the tuber tissue; withdrawing said tubers from said fluid and bringing them to a cooling zone; and preferably introducing said tubers into a cooling fluid at a temperature at or below ambient temperature, preferably below 200C, most 0 preferably below 10 C, in said cooling zone so as to substantially wholly surround the individual tubers in said cooling fluid, so as to rapidly cool said tubers to a temperature at or below ambient temperature, preferably below 200C, most preferably below 100C; and withdrawing said tubers from said cooling zone. Where the thermal treatment fluid is water (including dilute aqueous solutions) the tubers are preferably immersed in said fluid for a period of from 30 seconds at a temperature in the region of 650C to 10 minutes at a temperature in the region of 500C. The cooling step is preferably carried out so that said tubers are cooled to said temperature within a period of not more than 15 minutes, preferably from 4 to 12 minutes, e.g. 5 to 10 minutes. In practice it will often be sufficient to use ambient air, optionally with assisted flow, as the cooling fluid. Desirably the thermal treatment is carried out under temperature and time conditions such that substantially only the outer, extra-vascular, region of the tuber is heated. Advantageously the thermal treatment is carried out under temperature and time conditions such that the viability of the tuber with respect to sprouting is substantially unimpaired although in the case of ware tubers this is of course not essential. With the method of the present invention it is possible to effectively control potato blackleg in a commercially acceptable manner without significantly impairing the quality of the tubers for ware purposes and/or for seed purposes. Desirably the tubers are treated shortly after. lifting, e.g. within 1 month, in order to minimise any development of disease in the tubers and to maximise viability especially in relation to sprouting. In practice though it has been found that the tubers may be successfully treated in accordance with the invention up to 3 months or even 6 months after lifting. In a further aspect the present invention provides an apparatus suitable for use in the method of the present invention in the treatment of tubers and/or other like vegetable material of generally similar form, which apparatus comprises a vessel having a water holding zone, an endless conveyor means formed and arranged for conveying said tubers or the like along a conveying path having a substantial portion within said water holding zone between a conveyor loading station and a conveyor discharge station; water circulation means formed and arranged for circulating water, in use of said apparatus, so as to circulate water through said conveyor path portion, water heating means formed and arranged for heating, in use of the apparatus, said water being circulated and temperature control means formed and arranged for maintaining, in use of the apparatus, 0 the temperature of said water at from 50 to 65 C; and conveyor drive control means formed and arranged for controlling the speed of said conveyor means so as to determine the transit time between said loading and discharge stations thereby determining the residence time in said water holding zone, said conveyor means having tuber support and retaining means of generally open-work structural form so as to permit water flow therethrough to substantially all sides of said tubers, said conveyor means being further formed and arranged so as to tumble and/or roll said tubers at least along a substantial part of said conveyor path portion. Thus with an apparatus of the present invention it is possible to thermally treat tubers and the like against temperature sensitive diseases in a closely controlled manner such as to permit substantially complete and effective treatment on a continuous basis of large amounts of tubers without significant injury to the tissue of the tuber. The water circulation means may be in the form of one or more discrete units but could also be constituted by suitably disposed heating means whereby water circulation is effected by convection currents and/or by the conveyor means whereby water circulation is effected by movement of the water by the conveyor means during movement of the conveyor means. Preferably the conveyor drive control means includes temperature sensor means formed and arranged for substantially continuously monitoring, in use, the temperature of the water during conveying of tubers therethrough, and is arranged for varying the speed of the conveyor means in a predetermined proportional relation to the temperature whereby the transit time of the tubers is varied in an inverse relation with respect to said temperatures. Further preferred features and advantages cf the invention will appear from the following detailed description given by way of example of a preferred embodiment illustrated with reference to the accompanying drawings in which: Fig. 1 is a generally schematic sectional elevation of a tuber treatment apparatus of the invention; Fig. 2 is a detail transverse section of part of the conveyor means of the apparatus of Fig. 1; and Figs. 3 and 4 are corresponding views of a second apparatus of the invention. Fig. 1 shows an apparatus 1 suitable for use in the treatment of potato blackleg. The apparatus 1 comprises a thermally insulated tank 2 having mounted therein a conveyor means 3. The conveyor means 3 is in the form of a large wheel 4 having along its outer circumference 5 an outwardly facing general U-shaped section guide channel 6 engaged by a plurality of circumferentially spaced apart guide wheels 7 and one or more drive wheels 8. As may be seen in Figure 1, the wheel 4 is mounted in a vertical plane with a small outer portion 9 extending above a water holding zone 10 below the water level line 11. In more detail the wheel 4 has a generally hemicylindrical section (see Fig. 2) and is sub-divided by divider plates 12 which extend radially, into a plurality of tuber receiving compartments 13. The radially outer sides 14 of the compartments are defined substantially by a plurality of substantially spaced apart flexible elements such as plastic covered rope 15. The radially inner sides 16 of the compartments are partly open 17 and partly enclosed at the downstream ends 18 by a plurality of spaced apart axially extending elements 19 (note that the elements 15 and 19 of only some of the individual compartments are shown). The drive motor 20 is connected by a suitable transmission means to the drive wheel 8 for rotating the wheel 4 clockwise (as viewed in Fig. 1). As may be seen in Fig. 1, the loading chute 21 extends downwardly into the water holding zone 10 to feed tubers 22 into the wheel, at a conveyor loading station 23 positioned so that the tubers fall gently into the compartments 13 and are retained therein, as the individual compartments traverse a conveyor path 24 through the water holding zone 10. In order to protect the tubers against physical damage by trapping between the axial elements 19 and the discharge end 25 of the chute 21, the latter is urged into its loading position by resilient biasing means 26 so that if a tuber should become trapped, the chute backs away from the wheel riding over the trapped tuber 22. At the upper part of the wheel above the water level line 11 is provided a discharge chute 27 which is mounted so as to catch tubers falling out of the compartments as these traverse the uppermost part of the conveyor path. The tank 2 is also provided with water heating means, conveniently in the form of one or more immersion heaters 28 and water circulation means, for example a water pump 29 mounted in a water circulation conduit 30. It will be appreciated that the representation of the latter is somewhat schematic since it is important that the heating and circulation means should be arranged so as to provide 0 as uniform and constant temperature (ca.52 C) in the water holding zone 10 and to maximise and make as uniform as possible the thermal transfer between the water and the tubers. Detailed arrangements may be readily determined by simple experiments. The tank 2 is also provided with a temperature sensor 31 connected to a control means 32 for continuously monitoring the water temperature and varying the speed of the motor 20 in response thereto so as to adjust the tuber residence time in the water in accordance with any variance in temperature of the water, so as to ensure at all times an optimum thermal treatment of the tubers. Thus the motor needs to be readily and precisely adjustable in speed and in this connection a hydraulic motor or possibly a pneumatic motor, is found to be particularly suitable. It will be appreciated that as the tubers are carried round along the conveyor path 24 by the wheel 4 they are subjected to a gentle tumbling action and also to a continuous flow of water thereover thereby ensuring a substantially rapid and even thermal transfer between the water and the surface layer of the tuber. The discharge conveyor 27 extends to a cooling apparatus (not shown) formed and arranged for rapid cooling of the tubers. Conveniently the cooling apparatus comprises tuber conveyor means, conveniently in the form of a pintle belt with. upstanding rubber or other more or less soft resilient deformable fingers on which the tubers are supported as they pass through a cooling zone in which cold air is blown over and around them by suitable air flow induction means such as fans to provide a rapid cooling and all-over drying of the tubers. Alternatively in order to achieve a possibly even more rapid cooling of the tubers these could be conveyed into a further apparatus substantially similar to that shown in fig. 1 in which, though, the water is maintained at a relatively low temperature e.g. 50C, and the heating elements 28 are replaced by refrigeration elements. If required, the tubers could then be subsequently dried by blowing air over them. Although the above apparatus has been described with reference to the treatment of potato tubers, it may also be used for the treatment of other vegetable matter such as for example bulbs and soft fruit such as apples. In addition, if desired for example in order to treat other diseases or parasitic contamination e.g. infestation with nematodes, one or more chemical agents may be included in the water through which the tubers are conveyed. It will also be appreciated that various modifications may be made to the above apparatus without departing frcm the scope of the present invention. Thus, for example, in order to minimise any substantial temperature gradients in the surface layer of the water which could prejudice the accurate control of the thermal treatment, additional thermal insulation could be provided, fcr example in the form of a layer of polystyrene beads or the like floating on the surface of the water. Also in order to maximise thermal efficiency, the wheel 4 is preferably constructed of materials having a relatively low thermal capacity in order to limit heat loss at the upper section of the conveyor path. Where the apparatus is to be used for smaller sized plant matter such as for example flower bulbs, then the mesh size of the compartment walls would need to be reduced. It should incidentally be noted that where the plant matter is intended to be stored for any period of time prior to planting or consumption, then it is important that a drying step should be included for by one or more means as indicated above. In Figs. 3 and 4 like parts corresponding to those in Figs. 1 and 2 have been identified by like reference indices. Also some items have been omitted to a greater or lesser extent for greater clarity. In this case the tank 2 is mounted on a wheel chassis 40 suitable for towing by a motor vehicle so that the apparatus can be readily moved between different sites as required for use in treatment of tubers lifted at different places. Also, the radially inner periphery of the wheel 3 is open and instead there is provided a fixed support in the form of a plurality of elongate arcuate round section elements 41 disposed in side-by-side relationship adjacent the radially inner edges 42 of the divider plates 12 of the wheel 3. Conveniently the elements 41 are in the form of tubes of a plastics material such as a polyamide or polypropylene which is relatively wear resistant and forms a low friction contact with the divider plates 12 which conveniently are made of rigid or semi-rigid rubber or plastics. This arrangement has been found to be particularly gentle on the tubers being treated. As may be seen in Fig. 3 the fixed elements 41 are splayed out at one end 43 to form a hopper 44 for receiving tubers at the loading station 23 from the loading chute 21, and extend around the inner periphery of the wheel 3 in sliding contact with the divider plates 12 up to the discharge station 27, so as to define together with the wheel 3 a plurality of tuber receiving compartments 13. The loading chute 21 is connected to a loading conveyor 45 (indicated schematically) which conveys the tubers 22 through a cleaning station 46 where any soil is removed to a greater or lesser extent in order to maximise thermal contact of the heated water 10 with the tuber itself during the thermal treatment. Conveniently the tubers are washed by spraying and/or immersion and desirably passed though a water bath in which they are subjected to ultrasonic radiation which assists in removal of the soil. At the discharge station 27 there is provided a suitable belt conveyor 47 for conveying the thermally treated tubers to a cooling and optionally drying also, station 48. In practice it has been found that since tuber lifting is carried out in the Autumn, the tubers are cooled and dried sufficiently rapidly by passage along a short conveyor run of a few metres through ambient air so that they may be conveyed directly to a bagging station and cooling and drying allowed to continue naturally in the sacks especially where these are of hessian or like woven material. If desired there may be provided a mechanically assisted air flow through or across the discharge conveyor 47 downstream of the tank 2. The tank 2 is normally provided with an insulated roof 49 to help maintain a uniform temperature and conserve energy. Suitable inlet and outlet openings, inspection hatches etc are provided as required and provided with suitable seals etc. The drive system 20, 8 may be driven by any suitable means such as for example an electric or more conveniently a hydraulic motor to provide a suitable rate of rotation e.g. about i r.p.m. to provide a residence time of 3 minutes 3 in a typical arrangement using a 10 m capacity tank holding some 8 tonnes of water. This can achieve a treatment rate of the order of 3 tonnes of tubers per hour. As maintained hereinabove the treatment water may include suitable chemicals for simultaneous treatment of other possible conditions such as potato gangrene (Phoma exigua), black scurf (Rhizoctonia solami), powdery scab (Spongospora subterranea) etc which might also be present. Thus for example thiabendazole may be included in the treatment water. As mentioned above the temperature and treatment time may be varied within the limits specified. Typical conditions which have been found satisfactorily maintained sprouting ability were 3 mins at 550C and 5 mins at 520C. Advantageously filter means may be provided, conveniently in the water circulation means, for avoiding buildup of soil shed from the tubers in the tank. It may also be noted that where a longer treatment time e.g. up to 30 mins would be acceptable then a treatment temperature as low as 450C could be used.

Claims: CLAIMS 1. An apparatus (1) suitable for use in the treatment of tubers (22) and/or other like vegetable material of generally similar form so as to control disease therein, which apparatus comprises a vessel (2) having a water holding zone (10), an endless conveyor means (3) formed and arranged for conveying said tubers (22) or the like along a conveying path having a substantial portion within said water holding zone (10) between a conveyor loading station (23) and a conveyor discharge station (27); water circulation means (29) formed and arranged for circulating water, in use of said apparatus (1), so as to circulate water through said conveyor path portion, water heating means (28) formed and arranged for heating, in use of the apparatus, said water being circulated and temperature control means (28) formed and arranged for maintaining, in use of the apparatus, the 0 temperature of said water at from 50 to 65 C; and conveyor drive control means (20, 32) formed and arranged for controlling the speed of said conveyor means (3) so as to determine the transit time between said loading and discharge stations (23,27) thereby determining the residence time in said water holding zone (10), said conveyor means (3) having tuber support and retaining means (14-19) of generally open-work structural form so as to permit water flow therethrough to substantially all sides of said tubers (22), said conveyor means (3) being further formed and arranged so as to tumble and/or roll said tubers (22) at least along a substantial part of said conveyor path portion. 2. Apparatus according to claim 1 wherein is provided at an upstream end portion-a soil removal zone (46) formed and arranged for cleaning of the tubers in use of the apparatus. 3. Apparatus according to claim 1 or claim 2 wherein said conveyor means is in the form of a wheel (4) having axially outer annular end wall means and radially outward wall means (15), and a plurality of generally radially extending compartment defining wall means (12) for defining a plurality of tuber holding compartments, and provided with radially inward wall means (16) formed and arranged to retain said tubers within said compartments between said loading and discharge stations (23,27) whilst permitting entry and exit, respectively, at said stations (23,27). 4. Apparatus according to claim 3 wherein said radially inward wall means is fixedly mounted so as to extend along the radially inward periphery of the wheel between said loading and discharge stations (23, 27) in sliding contact with said wheel (3). 5. Apparatus according to any one of claims 1 to 4 wherein the conveyor drive control means (32, 20, 8) includes temperature sensor means (31) formed and arranged for substantially continuously monitoring, in use, the temperature of the water during conveying of tubers (22) therethrough, and is arranged for varying the speed of the conveyor means (3) in a predetermined proportional relation to the temperature whereby the transit time of the tubers (22) is varied in an inverse relation with respect to said temperature. 6. Apparatus according to claim 1 or claim 2 wherein said conveyor means is a vibrator type conveyor having a vibrator drive for vibration of said tuber support means and a conveying path formed and arranged so that the tubers are conveyed along said path under the influence of the weight of tubers (22) entering said path at said loading station (23) during operation of said vibrator drive. 7. A method of treatment of potato blackleg in potato tubers comprising the steps of: grading potato tubers (22) according to size, bringing size-graded potato tubers (22) of a similar size, at a temperature at or below ambient temperature, to a thermal treatment zone (10); introducing said tubers into a body of thermal treatment fluid having a thermal capacity substantially Ja-ger than that of said introduced tubers (22) such that said introduced tubers have a substantially negligible effect on the temperature of said fluid which fluid is at a temperature of from 50 to 650C, so as to substantially wholly surround the individual tubers with said fluid, and retaining said tubers in said fluid for a period of time sufficient to substantially kill the blackleg organism without significantly damaging the tuber tissue; withdrawing said tubers from said fluid, and bringing them to a cooling zone. 8. A method according to claim 7 which includes the steps of introducing said tubers into a cooling fluid at a temperature at or below ambient temperature, in said cooling zone so as to substantially wholly surround the individual tubers in said cooling fluid, so as to rapidly cool said tubers to a temperature at or below ambient temperature, and withdrawing said tubers from said cooling zone. 9. A method according to claim 7 or claim 8 wherein the tubers are immersed in an aqueous thermal treatment fluid for a period of from 30 seconds at a temperature in the region of 650C to 10 minutes at a temperature in the 0 region of 50 C. 10. A method according to any one of claims 7 to 9 wherein the thermal treatment is carried out under temperature and time conditions such that substantially only the outer, extra-vascular, region of the tuber is heated. 11. A method according to any one of claims 7 to 10 wherein the thermal treatment is carried out under temperature and time conditions such that the viability of the tuber with respect to sprouting is substantially un-impaired.

Inventors: MACKAY, JAMES MURDOCH, MELVIN, JAMES STEWART
Applicants: ABERDEEN BIO-TECH LIMITED
Application year: 1985
Main classification: A01C1
IPC codes: A01C1, A23N12