Plant Manipulation. Level 4. Copyright. Manage Plant Manipulation Methods of Citrus Agriculture and Nature Conservation

Transcription

1 Plant Manipulation Level 4 Copyright P.O. Box 461, Hillcrest, 3650 Title: Manage Plant Manipulation Methods of Field: Agriculture and Nature Conservation Sub-Field: Primary Agriculture SETA (SGB): PAETA Skills Area: Plant Manipulation Context: Farming US No: Credits: 3

2 Table of Contents Directions... 3 Introduction... 4 Chapter Introduction Plant Manipulation Tool Troubleshooting Plant Growth Stage Equipment Maintenance Chapter Introduction Manipulation Methods Manipulation and Framework Development Troubleshooting Cutting Procedures Initial Shaping Secondary Shaping Maintenance Pruning Manipulation of Growing Points Managing Tree Shaping General Factors Shaping Young Trees Pruning Bearing Trees Staff Chapter Introduction Managing Fruit and Flower Manipulation Flower and Fruit Set Manipulation Fruit Thinning Quality Manipulations Creasing Establishing a Spraying Program Wind Strength and Direction Temperature Available Daylight Hours Physical Fruit Manipulation Chapter Introduction Hygiene of pruning equipment Hygiene in the orchard Considering maximum residue levels and food safety during chemical plant manipulation actions Bibliography

3 Directions This material is aimed at learners wishing to complete this unit standard. The guide contains all necessary learning to ensure that the learner will attain the competencies expected from learners for this unit standard. The guide was designed to be used by a learner during the presentation of a skills program based on the unit standard, and to be retained afterwards for reference purposes. Although this guide contains all the information required for attaining competency in this unit standard, references to additional resources, both printed and electronic, are provided for further study by the learner. Use the icons listed below for identification purposes: 3

4 Introduction 1. Purpose A learner achieving this unit standard will be able to implement a plant manipulation management plan using a broad range of techniques. Learners achieving this unit standard will be able to apply their skills and capacity in a variety of production environments and be able to contribute towards to overall productivity of a production enterprise by maximising growth and yield and maintaining high standards of practice. Learners will gain specific knowledge and skills in plant manipulation processes and will be able to operate in a plant production environment implementing sustainable and economically viable production principles. They will be capacitated to gain access to the mainstream agricultural sector, in plant production, impacting directly on the sustainability of the sub-sector. The improvement in production technology will also have a direct impact on the improvement of agricultural productivity of the sector. 2. Learning Assumed to be in Place It is assumed that the learner has successfully completed the unit standards listed below: NQF Level NQF3 Unit Standard Number Literacy and Numeracy Monitor plant manipulation Unit Standard Description Explain the planning and scheduling of tasks in a production environment Demonstrate a basic understanding of the physiological processes in plant growth and development 4

5 Revision of Level 3 Revision of Level 3 Monitor and supervise the use of appropriate tools / equipment for pre-determined manipulation methods By means of the correct plant manipulation technique or method, trees can be encouraged to produce a product the market desires. Selecting the correct tool for the task at hand and using it in the correct way is very important, because it saves time, it limits the threat of damage to the tree, and it limits the threat of injury to the worker. A lot of plant manipulation tools have blades and it can cause serious injury to a worker that is not trained in its correct use. Monitor and supervise framework development principles as part of plant manipulation methods Although citrus trees are generally not trellised, it is necessary that you have an understanding of how and why other crops are trellised. Trellising systems consist of poles and wires that are arranged in a specific configuration. Fruit trees and vines are trellised for a variety of reasons. Different methods of trellising exist for different deciduous crops, each with a unique application and according to the individual requirements of the crop. Monitor and supervise flower and fruit manipulation Flower manipulation as such is not generally practiced in citrus cultivation. Fruit manipulation is however used extensively, in terms of fruit set and fruit size manipulation, and during harvest time. The most commonly used fruit manipulation methods are aimed at fruit set manipulation, fruit thinning, fruit size manipulation, delaying the harvest, and creasing control. Gibberellic acid sprays around petal fall increase the sink strength, which is the mobilisation of nutrients which promotes fruit set, of the fruitlets. On mature trees, fruit thinning agents are used to thin the crop by causing the smaller fruit to abscise (fall off). Fruit enlargement products improve the transport of energy and other resources towards the fruit. Applying gibberellic acid maintains the quality of the fruit for longer before being harvested. Picking of grapefruit and lemons can be delayed by up to three to four weeks with the use of gibberellic acid with the addition of 2,4D, which delays fruit abscission. Gibberellic acid can be applied to the fruit to delay the onset of creasing. Gibberellic acid is the main chemical that is used during chemical plant manipulation and there are a number of products on the market that contain gibberellic acid and other plant manipulation chemicals. All chemicals should be considered hazardous unless indicated otherwise, and when PPPs are being applied, health and safety regulations must be strictly observed. 5

6 Monitor and supervise pruning as vegetative plant manipulation methods appropriate to the crop With correct pruning and skirting, unwanted growth can be removed, resulting in better light interception and a more productive tree with an improved yield, fruit size and quality, and improved pest and disease control. The main vegetative manipulation methods used in citrus production are pruning, skirting, and girdling. Pruning is done mainly to improve light penetration, tree size and shape, general tree health, and production activities. Improved light intensity increases sprouting and improves flower and bearing wood quality. Tree size is in the end the grower s choice, and will depend on the tree spacing, the equipment that is available, and a number of other factors. Judicious pruning maintains the tree in a continual growth phase, as opposed to a devitalised or declining state. By keeping tree diameter in check though pruning, roadways are kept open, minimising damage to branches and fruit from tractors and other farm equipment. Trees are skirted to keep branches and fruit off the ground. Girdling is used to increase fruit set by the mechanical disruption of the flow of nutrients in a tree. The manner in which trees are pruned depends on the tree size and tree age, because the purpose of pruning changes with the tree age. Hedging removes foliage off the sides of the trees and topping removes the tree tops horizontally. 6

7 Chapter 1 After completing this chapter, the learner will be able to: Interpret a plant manipulation management plan 1. Introduction In the southern African citrus industry the manipulation of citrus trees is not widely practiced. This is due to the belief that the majority of the traditional commercial citrus cultivars seldom require major attention. Pruning is the only common manipulation method used to control tree size and thereby ease harvesting. Pruning practices such as hedging and topping is used to control tree size whilst either pruning practices are used to manipulate crops by adjusting fruit size through fruit set manipulation and by rejuvenating trees. However, with the growth of the soft citrus industry in southern Africa more particular attention is given to the shaping of trees through pruning. Soft citrus trees are more likely to become overgrown with foliage and the need to prune trees to increase sunlight penetration and thereby the internal and external quality of fruit is critical to ensure profitability. On a citrus farm the plant manipulation plan forms part of the integrated fruit production plan that are used to managed the citrus farm. The plant manipulation plan can include practices such as framework development, to increase sunlight penetration in trees, or pruning practices to manipulate fruit set and fruit size. Other practices that can form part of the plant manipulation plan is the selection and maintenance of tools used during the manipulation. 2. Plant Manipulation Tool Troubleshooting Selecting the correct tools to implement the methods define in the plant manipulation plan is important to ensure the correct implementation of a fruit manipulation plan. The selection and the correct use of the tools are described in the level 2 and 3 learner guides; in this guide we will have a look at the common problems that occur during the use of this equipment and solution to these problems. Table 1.1 gives a list of tools commonly used in plant manipulation as well as common problems and solutions. Tools / Equipment Problem Solution Pruning shears Lopping shears Blades are not sharp Shear is loose Branch is too thick Tool is not sterile Blades are not sharp Shear is loose Branch is too thick Choose correct tool: o Pruning shears: cuts branches up to 20mm thick o Lopping shears: cuts branches up to 30mm thick o Bow saw: cuts branches thicker than 30mm o Pruning saw: cuts branches thicker than 30mm, cleaner cut Use tools according to instructions Regularly check sharpness and tension of blades Sterilise tools regularly, especially when moving between orchard blocks Choose correct tool: o Pruning shears: cuts branches up to 20mm thick 7

8 Tools / Equipment Problem Solution Bow saw Pruning saw Tool is not sterile Blade is not taught Blade is twisted Blades are not sharp Push instead of pull o Lopping shears: cuts branches up to 30mm thick o Bow saw: cuts branches thicker than 30mm o Pruning saw: cuts branches thicker than 30mm, cleaner cut Use tools according to instructions Regularly check sharpness and tension of blades Sterilise tools regularly, especially when moving between orchard blocks Choose correct tool: o Pruning shears: cuts branches up to 20mm thick o Lopping shears: cuts branches up to 30mm thick o Bow saw: cuts branches thicker than 30mm o Pruning saw: cuts branches thicker than 30mm, cleaner cut Use tools according to instructions Regularly check sharpness and tension of blades Sterilise tools regularly, especially when moving between orchard blocks Choose correct tool: o Pruning shears: cuts branches up to 20mm thick o Lopping shears: cuts branches up to 30mm thick o Bow saw: cuts branches thicker than 30mm o Pruning saw: cuts branches thicker than 30mm, cleaner cut Use tools according to instructions Regularly check sharpness and tension of blades Sterilise tools regularly, especially when moving between orchard blocks Wound sealant Sealant is phytotoxic Ensure suitable for citrus Apply with sterilised brush Ensure that sealant is stored in the prescribed manner. Ladder Mulching equipment Sterilising agent Rungs or posts are broken Ladder is painted Ladder is too short Ladder is not stable Tractor is too small Branches are too thick to be mulched Diseases are spreading from orchard to orchard. Use suitable ladder Ensure rungs and side-posts are strong and not broken Painted ladders introduce foreign object to the orchard as paint chips can pollute fruit. Use mulcher according to tractor size Set the mulcher blades to the correct setting to handle branch thickness. Ensure that the correct concentration of sterilising agent is used. 8

9 Tools / Equipment Problem Solution Carpet or utility knife Girdling saw or knife Girdling pliers Fruit count frame Fruit measuring callipers Cut is not a clean Cut is not right around the trunk Cut is too deep Blade is too thin or too thick Blade is not sharp Bark is loosened or removed Tool is not sterile Cut is not a clean Cut is not right around the trunk Cut is too deep Blade is too thin or too thick Blade is not sharp Bark is loosened or removed Tool is not sterile Cut is not a clean Cut is not right around the trunk Cut is too deep Blades are not sharp Blades do not turn freely Bark is loosened or removed Tool is not sterile Frame is not deep enough in tree Right tree is not selected Frame is not appropriate Callipers are not used correctly Measurement is taken in jaw recesses Table 1.1: Plant Manipulation Tools and Equipment Ensure that the correct contact time of agent and the equipment are achieved. Ensure that the sterilising agent is not out of date. Cut right around the trunk Cut at correct height Cut only the bark Do not loosen or remove the bark Sterilise after use Cut right around the trunk Cut at correct height Cut only the bark Do not loosen or remove the bark Sterilise after use Adjust pliers to correct size Cut right around the trunk Cut at correct height Do not loosen or remove the bark Sterilise after use Select the right trees Insert properly into tree Select the appropriate size frame to suit the tree. Read instructions for specific callipers Know how to slide and read callipers 3. Plant Growth Stage Different plant manipulation methods are designed to be used at different growth stages of plant and tree development. If a manipulation method is applied at the incorrect growth stage of the tree or plant it can cause irreparable damage to the plant and thereby huge financial loses to the grower. Table 1.2 gives a list of manipulation methods commonly used on the citrus farm and a guideline as to when these actions should be performed. Manipulation Method Growth Stage Pruning Tree shape and size are manipulated during the first three years of tree development. Windows to improve sunlight penetration are made during the summer high growth stage. Hedging and topping are done after harvesting. New unwanted growth removal takes place during the year. 9

10 Skirting Girdling Manipulation Method Fruit Thinning Fruit Set Manipulation Fruit Size Enlargement Delaying Harvest Growth Stage Any time of the year but not after final fruit set. In the summer during the high growth stage. Depending on the chemical used, but normally after initial physiological fruit drop. Bt may be done earlier if more fruit must be removed Depending on the chemical used but usually around petal fall. Depending on the chemical used, but normally after initial physiological fruit drop. The chemical application usually takes place at the start of the 3 rd fruit development stage. The later the application the less of an effect of the delaying chemical will have. Creasing Control At the first appearance of creasing. Table 1.2 Manipulation Methods and Plant Growth Stages. 4. Equipment Maintenance The maintenance of equipment used during the application of the various manipulation methods is important to ensure that the plant manipulation plan is efficiently implemented in a cost effective manner. By maintaining equipment sufficiently a grower can ensure that equipment last longer and be ready for use when necessary. The design and implementation of a maintenance schedule is critical in order to ensure that the necessary maintenance tasks and duties are performed at the correct time and in the correct manner. The implementation of the maintenance schedule must be monitored and managed by the design of a recordkeeping system and the capturing and analysis of the data obtained through these records. Table 1.3 lists the equipment that is normally used to implement plant manipulation methods and the maintenance practice that should be employed in order to achieve ensure that equipment lasts longer. Tools / Equipment Maintenance Tasks Schedule Pruning shears Lopping shears Bow saw Pruning saw Sharpen blades. Sterilise equipment. Lightly oil hinges. Sharpen blades. Sterilise equipment. Lightly oil hinges. Sharpen blade or replace if necessary. Sterilise equipment. Sharpen blade or replace if necessary. Ensure blade tension is correct. Sterilise equipment. Blade should be sharpened when necessary but at least twice a year. Equipment must be sterilised after use and when moving between orchards. Hinges must be oiled before use and before storage. Blade should be sharpened when necessary but at least twice a year. Equipment must be sterilised after use and when moving between orchards. Hinges must be oiled before use and before storage. Blade should be sharpened when necessary but at least twice a year or replaced if bend. Equipment must be sterilised after use and when moving between orchards. Blade should be sharpened when necessary but at least twice a year or replaced if bend. 10

11 Tools / Equipment Maintenance Tasks Schedule Ladder Mulching equipment Carpet or utility knife Girdling saw or knife Girdling pliers Tighten hinges. Check steps for stability. Service tractors. Service mulching equipment. Strip and clean mulching equipment. Replace blades when necessary. Sterilise equipment. Sharpen blade or replace if necessary. Sterilise equipment. Sharpen blades. Sterilise equipment. Lightly oil hinges. Blade tension must be check before use and relaxed after use. Equipment must be sterilised after use and when moving between orchards. Ladder must be checked before and after use. Tractors must be serviced at least once a year. Mulching equipment must be stripped and cleaned after use. Mulching equipment must be serviced in agreement with the supplier s recommendations. Fruit count frame Sterilise equipment. Sterilise after use. Blade should be replaced when necessary but at least twice a year. Equipment must be sterilised after use and when moving between orchards. Blade should be sharpened when necessary but at least twice a year or replaced if bend. Equipment must be sterilised after use and when moving between orchards. Blade should be sharpened when necessary but at least twice a year. Equipment must be sterilised after use and when moving between orchards. Hinges must be oiled before use and before storage. Fruit measuring callipers Calibrate regularly. Calibrate as per supplier s instructions. Table 1.3 Equipment Maintenance 11

12 Chapter 1 On a citrus farm the plant manipulation plan forms part of the integrated fruit production plan that are used to managed the citrus farm. The plant manipulation plan can include practices such as framework development, to increase sunlight penetration in trees, or pruning practices to manipulate fruit set and fruit size. Other practices that can form part of the plant manipulation plan is the selection and maintenance of tools used during the manipulation. Selecting the correct tools to implement the methods define in the plant manipulation plan is important to ensure the correct implementation of a fruit manipulation plan. The selection and the correct use of the tools are described in the level 2 and 3 learner guides; in this guide we will have a look at the common problems that occur during the use of this equipment and solution to these problems. Different plant manipulation methods are designed to be used at different growth stages of plant and tree development. If a manipulation method is applied at the incorrect growth stage of the tree or plant it can cause irreparable damage to the plant and thereby huge financial loses to the grower. The maintenance of equipment used during the application of the various manipulation methods is important to ensure that the plant manipulation plan is efficiently implemented in a cost effective manner. By maintaining equipment sufficiently a grower can ensure that equipment last longer and be ready for use when necessary. Complete activity * in the Learner Workbook. 12

13 Chapter 2 After completing this chapter, the learner will be able to: Create and implement a plant manipulation schedule 1. Introduction The method of managing a citrus growing operation preferred by the southern African citrus grower is the development of an Integrated Fruit Production system or IFP plan. The IFP plan contains various management plans that cover all the various aspects of a successful citrus producing operation. The integration of the various plans is an important factor in ensuring the profitability of the citrus enterprise. Part of the IFP plan is the plant manipulation plan and schedule. The design and development of the plant manipulation plan is a critical part in ensuring that the optimum yield and fruit quality is obtained from the citrus orchard. Traditionally very few plant manipulation methods are used in the citrus industry in southern Africa, but with the citrus industry becoming more and more competitive it is important for a grower to ensure that the optimum yield and fruit quality is obtained from every tree. The most commonly used method of manipulation used in the various fruit industries are trellising. Trellising methods include systems such as, central leader systems, the Tattura system, the two wire system, the slanted cap, the factory-cap and the Façade system to name a few. In the citrus industry though the use of trellising systems has not been proven profitable and is not used. 2. Manipulation Methods Traditional commercial citrus varieties require minimal pruning and other manipulation methods in order to obtain the correct shape and size to ensure maximum yield and ease of harvesting. With the growth of the soft citrus industry and with the soft citrus export market showing major growth, soft citrus varieties and cultivars are becoming more and more popular. Soft citrus varieties, unlike the more traditional commercial citrus varieties, requires more shaping and pruning to ensure better sunlight penetration and thereby a better quality of fruit. Commonly the manipulation methods used in the citrus industry in southern Africa are: Tree Shaping methods such as o Framework Development o Window Cutting o Tree Rejuvenation o Hedging o Topping Skirting Girdling Fruit Set Manipulation through Flower Manipulation Fruit thinning Fruit size manipulation Delaying the harvest Creasing control 3. Manipulation and Framework Development Troubleshooting As discussed in the level 3 learner guide on Plant Manipulation the basic shaping of citrus trees takes place in the nursery during the first two years of tree development. During this time the basic framework of the tree is developed. Once planted in the orchard the trees are further shaped during the first six years. 13

14 After this period the framework of the trees are established and hedging or topping techniques are used to determine the size of the tree. Other pruning methods such as window cutting, skirting, hedging and topping used after the initial framework development period are only used to control the growth in the tree and have little influence on the tree shape. The management and monitoring of the following factors are important to ensure that the framework development processes in both the nursery and in the orchard are performed effectively: 3.1. Cutting Procedures Ensure that equipment used for pruning the trees are sharp. Blunt tools will cause branches to tear and thereby encourage infection. Ensure that equipment is sterilised after and before use and when moving between orchards. Unsterilized equipment can transfer diseases from plant to plant and between orchards leading to huge financial loses. All cuts must be covered using the correct sealant to discourage further growth and infection. Wood sealants must be appropriate to the variety and cultivar and be used according to the manufacturer s instructions Initial Shaping During initial shaping the stem of the tree where all new growth has been removed must be covered with PVA paint to limit sunburn and to prevent the occurance of suckers. Young trees must only be pruned and shaped once vigorous and strong growth is visible. Early pruning can affect tree growth negatively as leaves are necessary to produce the necessary carbohydrates to facilitate growth. When selecting scaffold branches only the growth tips of the branches must be removed. If the branches are removed totally tree growth will be stunted. Tree shaping must be done gradually. Not more than 20% of the total tree canopy must be removed at a time as this will adversely affect the trees ability to photosynthesise. The angle of the scaffold branches should between 30 and 55 degrees depending on the variety and cultivar of the trees. Spacers or weights can be used to shape branches initially until the branches harden. Branches must be monitored to ensure that no one branch become dominant and stunt the growth of other branches Secondary Shaping Secondary branches are selected during the third year of growth. The difference in height from the primary to the secondary branches should not exceed one metre Maintenance Pruning Most of the shaping activities should be completed by the fourth year. This is when the tree starts bearing fruit. Pruning should now only attempt to reduce upright growth whilst leaving horizontal shoots. Skirting is done to remove low hanging branches. Fruit hanging to low are likely to be infected by pathogens found in soil. Unwanted growth is removed to allow better sunlight penetration. The selection of the correct branches either leaders, branches growing upwards from tertiary forks, or hangers, braches growing horizontally from tertiary forks, is critical to ensure that the fruit load in the tree bear at the correct height to ease harvesting and prevent infection. 4. Manipulation of Growing Points Most pruning and manipulation of growth points must be done in the winter as soon as possible after harvesting. This is important to capitalise on inductive conditions thereby improving blossoming quality. 14

15 In young trees re-growth shoots or suckers are selected during the summer and shaped or arched by bending them to a 45 to 60 angle to the scaffold branch leading them out of the tree canopy towards the sunlight. These new suckers must not be lower than 1,5 meters of the ground as the fruit load will cause the branches to bend toward the ground. New growth is shaped by tucking the branches under other convenient branches. Undesirable growth is removed and the trees scaffold branches reduced to the desired number. It is not wise to remove all unwanted scaffold branches at the same time; this should be done over a period of two or three years. Tree height is also reduced where necessary but never with more than 0.5 meters. Tree should be kept to a height of about 3 meters with most of the fruit hanging within easy reach of pickers standing on the ground. The tree canopy must be thinned where necessary to increase light distribution within the tree and to allow sunlight to reach new growth. This process is called window cutting and strict hierarchy exist when choosing branches to prune: Firstly broken branches are pruned then The oldest branches then Branches bearing small yellow fruit then More healthy branches. Window cutting is best done from the inside out, thereby removing unsuited growth from inside the canopy firstly, working towards the outside. 5. Managing Tree Shaping When managing the tree shaping process the following factors are critical to remember: 5.1. General Factors Sealant must be applied to all cuts with a diameter of more than 3.0 centimetres. Limbs that were previously under shade must be whitewashed to limit sunburn. New flush growth must be protected from diseases such as thrips, aphids and psylla. Cutting instruments must be sterilised using a recommended sterilisation solution such as bleach or chlorine to limit the viroid transmission between trees and orchards Shaping Young Trees Commence tree shaping only from the end of the first year after planting. Shape the tree gradually. The scaffold branches must be spaced evenly around the stem and preferably at different heights. Ensure that inward growing branches are removed at an early stage Pruning Bearing Trees The inside of the tree must be accessible. Scaffold branches must be kept free of growth up to the third fork. Prune from the inside towards the outside without removing all the inside wood. Start pruning from the top hanger to the bottom hangers thereby gauging the sunlight penetration to the lower branches. Remove less vigorous growth from the underside of the hangers. Ensure that the tree is skirted at least 50cm of the ground by removing low hanging branches. Older trees must be pruned more severely. Remove watershoots or single branches which extend above the canopy of the tree by cutting them at the point where they originate. Where branches rub against each other the least desirable one must be removed. 15

16 All wood pruned from trees must be removed from the orchard and destroyed wither by burning or by chopping the wood up using wood cutters Staff Staff must be well trained in the correct pruning techniques. Staff must be issued with the correct protective clothing. Staff must be made aware of all the dangers connected to the use of pruning equipment. Staff must be trained in the correct use of sealant and sterilising solutions. Staff must always maintain the necessary personal hygiene levels. 16

17 Chapter 2 Part of the IFP plan is the plant manipulation plan and schedule. The design and development of the plant manipulation plan is a critical part in ensuring that the optimum yield and fruit quality is obtained from the citrus orchard.. Traditionally very few plant manipulation methods are used in the citrus industry in southern Africa, but with the citrus industry becoming more and more competitive it is important for a grower to ensure that the optimum yield and fruit quality is obtained from every tree. As discussed in the level 3 learner guide on Plant Manipulation the basic shaping of citrus trees takes place in the nursery during the first two years of tree development. During this time the basic framework of the tree is developed. Once planted in the orchard the trees are further shaped during the first six years. Most pruning and manipulation of growth points must be done in the winter as soon as possible after harvesting. This is important to capitalise on inductive conditions thereby improving blossoming quality. When managing the tree shaping process there are various factors that are critical to remember. Complete activity * in the Learner Workbook. 17

18 Chapter 3 After completing this chapter, the learner will be able to: Supervise the implementation of a plant manipulation schedule 1. Introduction In southern Africa fruit is grown in different regions under different climatic conditions. These climatic conditions also change from year to year and can influence the quality and yield of trees greatly. It is therefore important that the grower have the ability to adjust the carrying capacity of the citrus trees in the orchard to ensure that the maximum yield and fruit quality is obtained every year using the available natural resources and prevailing climatic conditions. A change in rainfall patterns and temperatures can lead to different fruit bearing patterns and thereby necessitates the grower to manipulate the flowering and fruit bearing patterns of the trees in the orchards. Changes in the internal and external quality parameter set by markets can also necessitate a grower to implement different fruit manipulation methods. For the citrus grower there are a range of methods available to manipulate flowering, fruit set and fruit internal and external quality. These include pruning practices and the application of chemicals at the correct stage of fruit or flower growth. The choice and management of the correct manipulation methods are critical to ensure the ultimate profitability if the citrus farm. 2. Managing Fruit and Flower Manipulation As discussed in the level 3 learner guide on plant manipulation different methods are used to manipulate the setting of fruit on tree and the quality of the fruit. In order to manage the different manipulation methods used and to determine their effectiveness a thorough and well documented recordkeeping system must be designed and put in place. The recordkeeping system must be designed in such a manner that the influence of the different manipulation methods have on either the fruit set or the fruit quality have can be measured and monitored. The responsibility of completing records and thereby monitoring the application of the various manipulation methods are the responsibility of the supervisors appointed to manage the manipulation processes. Supervisors must be well trained and motivated to ensure the effectiveness of manipulation practices. Supervisors must have a thorough understanding of manipulations methods and what the intended aims are of the applications of certain methods. Only by having a thorough understanding of the effect that the application of chemicals or the pruning of trees will have on tree development a supervisor will be able to perform the duties correctly. The supervision of plant manipulation practices is one of the often overlooked factors on a farm. Pruning and other manipulation methods is critical to ensure that the maximum yield and fruit quality is obtained from trees in the orchards. Pruning practices can severely damage a tree if pruning is done wrongly and the tools used for pruning is not sterilised. Blunt cutting tools can rip and tear branches thereby stunting the growth of the tree and lead to infection of limbs. Pruning performed at the wrong time can also damage trees severely and lead to financial loses. The following is a list of common manipulation practices and the areas where special attention must be given by supervisors. 18

19 2.1. Flower and Fruit Set Manipulation Different citrus varieties and even cultivars flower differently. For example shamoutis for instance produce 35,000 to 40,000 blossoms per tree and navels up to 200,000. The final fruit set depends on flowering intensity and flower quality. Only about 500 to 1,000 fruit are harvested per tree, with between 0.1% for a heavy blossom to 10% for a light blossom of the number of flowers finally become harvestable fruit. It is therefore important that the correct techniques are applied to the appropriate varieties and cultivars. A grower must obtain the necessary information pertaining to the optimum numbers of blossoms per tree for the varieties in his orchards and train his supervisors accordingly. Cold temperatures of 10 to 14 C during June and July produce a more intense, better blossom quality. High day temperatures of 25 to 30 C just before flowering, on the other hand, adversely affect floral development. Following a warm winter, flowering will be poor and probably protracted. The previous year s crop also influences flowering, because the amount of fruit carried by trees affects the flush. After a heavy crop, one is more likely to get less flush with a lot of flowers and poor reserves, resulting in a low crop. Very high temperatures and water stress can also result in trees losing their fruit during the fruit set period. It is thus important for a grower and his supervisor to take all these conditions into account when determining the need for the application of manipulation methods. Gibberellic acid sprays around petal fall increase the sink strength, which is the mobilisation of nutrients which promotes fruit set, of the fruitlets. In marginal production areas it is essential to spray gibberellic acid to ensure a good fruit set. Cooler areas need a no or low gibberellic acid application. A grower and supervisor therefore needs to constantly monitor the prevailing climatic conditions and predict the effect the condition will have on the flowering of tree and the set of fruit on the tree. This will determine the need for and the required intensity of chemical application Fruit Thinning For optimum fruit size the tree needs a minimum leaf to fruit ratio. If this ratio is too low, there are not enough nutrients to maintain fruit growth to maturity, resulting in a crop of small fruit. This fruit to leave ratio differs from variety to variety as well as from region to region. A supervisor therefore must be aware of the optimum leaf to fruit ration for his particular orchard. While the tree is still less than three years old, the fruit that it produces is often of inferior quality. It is however important that maximum vegetative growth is encouraged at this age, and for this reason all fruit on these trees should be stripped. If the fruit is left to mature, the weight of the fruit can also pull the tree over. On mature trees, fruit thinning agents are used to thin the crop by causing the smaller fruit to abscise. The tree can then use its available reserves to maintain the growth of the larger fruit. Fruit thinning also assists in improving fruit size uniformity. Fruit thinning is only done if the leaf to fruit ratio shows that the fruit load of the tree is excessive. The decision on whether to use this fruit thinning technique should be made on the basis of the number of fruit at the end of the physiological drop and the number of small fruitlets that should be removed. The more fruit that has to be removed, the earlier the application date should be. Early applications are also done as a rule in cooler areas, where the fruit is small overall, with small fruit cultivars, with trees in heavy soils, and in orchards with high yield potential. Later applications are used where fruit are medium in size, or with a low yield coupled with small fruit. The timing of the application of the fruit thinning agent is therefore critical to ensure the necessary results. 19

20 2.3. Quality Manipulations The major internal quality parameters that are measured to determine if fruit adheres to set standards are the juice content of the fruit as well as the sugar and acid contents. The development of juice sacks in the fruit is dependent on various factors but mainly the availability of moisture. Trees under any type of moisture stress produce fruit with less juice than fruit with sufficient natural sources. It is therefore critical that a grower are able to determine the optimum amount of fruit a tree will be able to bear and adjust the fruit count in the tree accordingly. The sugar content of the fruit is dependent on the breakdown of acids occurring in the fruit. The breakdown of acids occurs naturally in fruit and can be controlled by the application of certain growth hormones. It is therefore critical for the grower to constantly measure the levels of sugar and acids within the fruit in order to recognise when chemical application methods should be applied Creasing Creasing occurs normally in fruit that have suffered stress during the second phase of development. Creasing can be controlled a lessened by the application of growth hormones in the orchards. The state of fruit in the orchard must be constantly monitored in order to determine if the application of hormones is required to control the appearance of creasing. It is also necessary to determine the effect that the application of creasing control hormones will have on other internal and external parameters of the fruit and then to adjust production practices accordingly. 3. Establishing a Spraying Program In the citrus industry the same synthetically produced auxin or hormone is often used when manipulating different stages of fruit growth from the setting of fruit to the control of creasing. The timing of the application of the auxin is therefore critical in order to ensure the desired effect. Gibberellic acid is the main chemical that is used during chemical plant manipulation. Gibberellic acid is a hormone found in plants, and promotes the growth and elongation of plant cells, thereby promoting plant growth and size. Because gibberellic acid naturally regulates plant growth, an application of a very small volume can have a big effect, and applying too much of it can have the opposite effect. There are a number of products on the market that contain gibberellic acid and other plant manipulation chemicals. Farm management would normally consult an expert to determine when and how much of these products must be applied. These recommendations depend on the citrus cultivar and on the purpose of the application. Some recommendations are made based on timing, for instance how long it is after physiological fruit drop or before the expected picking date. Other recommendations are made based on the average fruit size, such as recommendations for fruit thinning and fruit size manipulation. The incorrect timing of applications can have a totally opposite effect to the one desired. Similar to the application of other agro-chemicals through spraying there are external factor that will influence the effectiveness of the application. These are: 3.1. Wind Strength and Direction A strong wind can severely influence the effectiveness of the spray application by blowing the spray away from the trees and onto other orchards where the application might cause damage Temperature 20

21 Some agro-chemical and plant manipulation products are more effective if applied at lower temperatures. Higher temperatures can cause excessive evaporation of sprayed chemicals and thereby lessen the effectiveness of the chemicals Available Daylight Hours Spray applications that are done later in the growth cycle can be dependent on the daylight hours that are available during the time of application. All spraying action can only be performed during daylight when driver can see where to apply the chemicals. It is also important that the equipment used for the application of plant manipulation chemicals are reserved only for that use and not be used for the application of other agro-chemicals such as pesticides or fungicides as well. The residues of chemicals left in spraying equipment can influence the effectiveness of the plant manipulation product and therefore increase the cost of applications. It is recommended that a grower keep and maintain separate spraying apparatus for the application of the different agro-chemicals. 4. Physical Fruit Manipulation In the southern African citrus industry physical fruit manipulation methods are rarely used. The only physical fruit manipulation method that is commonly practiced is the removal of fruit from young trees, under three years of age, as discussed earlier. On some farms general fruit thinning are also done physically but with the increase of the effectiveness of chemical auxin applications it is a practice that is become more and more rare. 21

22 Chapter 3 In southern Africa fruit is grown in different regions under different climatic conditions. These climatic conditions also change from year to year and can influence the quality and yield of trees greatly. It is therefore important that the grower have the ability to adjust the carrying capacity of the citrus trees in the orchard to ensure that the maximum yield and fruit quality is obtained every year using the available natural resources and prevailing climatic conditions. In order to manage the different manipulation methods used and to determine their effectiveness a thorough and well documented recordkeeping system must be designed and put in place. The recordkeeping system must be designed in such a manner that the influence of the different manipulation methods have on either the fruit set or the fruit quality have can be measured and monitored. In the citrus industry the same synthetically produced auxin or hormone is often used when manipulating different stages of fruit growth from the setting of fruit to the control of creasing. The timing of the application of the auxin is therefore critical in order to ensure the desired effect. In the southern African citrus industry physical fruit manipulation methods are rarely used. The only physical fruit manipulation method that is commonly practiced is the removal of fruit from young trees, under three years of age, as discussed earlier. On some farms general fruit thinning are also done physically but with the increase of the effectiveness of chemical auxin applications it is a practice that is become more and more rare. Complete activity * in the Learner Workbook. 22

23 Chapter 4 After completing this chapter, the learner will be able to: Maintain appropriate hygiene and health standards 1. Introduction As we discussed in the previous chapters there are several inherent dangers associated with in the application of manipulation methods. Some of the most critical of these dangers are the very real possibility of spreading diseases between orchards and the influence that the application of chemicals can have on the safety of the fruit for human consumption. When developing the plant manipulation plan a grower must consider all the factors that the application of certain methods will influence and adjust practices accordingly to allow for these influences. To ensure effective and safe manipulation a grower or supervisor must also design and implement methods to ascertain that the necessary health and hygiene standards are maintained in the orchard. 2. Hygiene of Pruning Equipment The majority of pruning practices takes place straight after the harvesting of fruit in the orchard. This is to ensure that use is made of the inductive conditions and thereby ensuring a better blossom quality. This is also the time of year when diseases and fungal growth can be at its most virulent in the orchard and therefore the possibility of infections spreading increases dramatically. To limit this spread of diseases and fungal growth a grower must implement a well supervised and documented sterilisation plan. The thorough sterilisation of cutting and other equipment used during plant manipulation is an important factor in ensuring that the appropriate health and hygiene standards are maintained in the orchard. Another important factor in limiting the spread of diseases is the strict implementation of a personal health and hygiene plan for all workers that performs pruning technique. Diseases and fungal spores can be transmitted between orchards by sticking to the hands of workers or by contact through clothing Sterilising Equipment Each farm or production area will have its own preferred way of sterilising equipment and the following guidelines are only an example of one of the more popular methods used for sterilising equipment in southern Africa. When using bleach as a sterilisation agent for effective sterilisation a solution of 1% of the active ingredient is needed. The water used for the sterilisation solution must have a neutral or as close to possible to neutral ph. If the ph of the water is too high the ph must be adjusted by adding an acid to the water until the desired ph of 7.2 is obtained. Once mixed the solution must be used within 5 hours and stored out of direct sunlight. Sunlight affects the effectiveness of the bleach adversely. To sterilise equipment wet the blade of the tool and allow the surface to air dry before use. The air drying of the surfaces ensure that the solution have a sufficient contact time and therefore eliminate the all the diseases or fungal spores that might be present. 23

24 All cutting tools must be sterilised at the start of the day before being used and directly after use. Tools must also be sterilised regularly, normally after 100 trees, and when moving between orchards. After use sterilised tools must be stored in a cool and dry area Personal Hygiene General personal hygiene rules must include the following: Nails must be kept short and clean. Fungal growth and other diseases can be trapped under long nails and be spread to other trees in this manner. Hands must be washed regularly using soap and water and especially when moving between orchards. Where possible workers should change into fresh clean overalls when moving between orchards. 3. Hygiene in the Orchard Another important factor that must be managed after trees have been pruned is the removal of the wood, leaves and fruit removed from the trees during pruning from the orchard. Organic material left in the orchard can become breading grounds for pests and diseases and lead to infestations. The removal of organic material from the orchard is a critical part of the orchard sanitation plan. The removal of organic material from the orchard are described in the orchard sanitation plan and subjected to several regulations that must be adhered to when disposing of the material. Incorrect disposal of organic material can lead to diseases infesting previously disease free orchards. Organic material removed from the orchard after pruning such as wood, leaves and fruit can either be burned in pre-prepared burning pits well that must be situated well away from the orchard or be chopped up using mulcher and buried in the prescribed manner. Chopped up organic material must be buried at least 400 meters away from the orchard and 30 centimetres deep. Care must also be taken that the burying of chopped up organic material does not adversely affect the soil nutrition program inadvertently. The introduction of organic material in the soil can lead to an increase of organic compounds and nitrogen in the soil. It is important that the grower and his supervisors document the removal process thoroughly to indicate that the removal and disposal process followed guidelines as stipulated by local and national legislation. Removal and disposal procedures must also adhere to stipulations as set apart in accreditation schemes such as good agricultural practice schemes. 4. Maximum Residue Levels To ensure that a citrus growing operation is profitable a large part of the citrus harvest must be exported to overseas markets. This necessitates a grower to be aware of the particular regulations and stipulations that their fruit must comply with before it can be exported to the specific overseas market. One of the most important parameters is the maximum residue level, or mrl, specifications. These are specification that stipulates the maximum amount of residues that any chemical should leave on the fruit in order to still make the fruit suitable for human consumption. Most market will specify levels for a range of agro-chemicals that traditionally only includes pesticide or fungicides. In some cases, and it is becoming more prevalent, the mrl levels include specification for chemicals used during plant manipulation as well. It is important to remember that all of these products have prescribed maximum residue levels and preharvest intervals. More information on these usage restrictions can be found in the Recommended Usage Restrictions for Plant Protection Products on Southern African Export document, issued by the CGA in conjunction with the CRI. A grower must therefore not only measure and take into account the influence pesticides and fungicides will have on MRL s but also the effect that the application of plant manipulation chemicals might have. 24