Agriculture for Engineers 4 (3+1)

Lesson 41. Pruning and Training

41.2 PRUNING

Pruning may be defined as the art and science of cutting away of portion of plant to improve its shape, to influence its growth, flowering and fruitfulness and to improve the quality of the product. It is done to divert a part of plant energy from one part to another part of plant.

41.2.1 Objects of Pruning:

• Training of young trees
• Maintenance of grown up trees i.e. to maintain the health of bearing plant
• Bringing vigour in old trees

41.2.2 Effect of Pruning

• It increases new vegetative growth
• In young trees flowering will be delayed
• In old trees there will be new vigorous vegetative growth which bears fruit
• It reduces bearing surface are as a result tree remain dwarf which is compensated by accommodating more number of dwarf trees (because pruning is a dwarfing process)
• Improvement in size, colour and quality of fruits

41.2.3 Principles of Pruning:

• Young trees are pruned to train it to acquire a desired shape.
• In old trees light heading back is done to stimulate the flowering
• In bearing trees light pruning is done to stimulate fresh growth. it bearing flower buds on fresh growth
• In old trees heavy pruning is done to restore vigorous
• All the diseased, weak, dead or shading branches must be removed.

41.2.4 Systems of Prunings

• Heading back: Only tops of branches are headed back or cut off (light pruning).
• Thinning out: Complete removal of a branches or a part
• Dehorning: Cutting away the main limbs or thick major branches
• Bulk pruning: Heavy pruning all over the tree. For good fruit production only judicious heading back or thinning out should be done.

 41.2.5 Rules of Pruning

• Never leave a stub as far as possible
• Minimum cut surface
• Start cutting from the lower end first, leave half way or even less and then cut from the top
• Keep the cut surface clean and smooth
• Protect the wound with Bordeaux paste.

 41.3 TRAINING:

It means developing a desired shape of the tree with particular objectives by controlling habit of growth. Training is start from nursery stage of plant. Some fruit crops like grape vines, ber, fig, guava etc require training.

41.3.1 Objects of Training:

• To admit more light and air to the centre of the tree to expose maximum leaf surface to the sun
• To direct the growth of the tree so that various cultural operations such as spraying, ploughing, harvesting can be performed easily and at lower cost.
• To protect the tree from sun burn and wind damage.
• To secure a balanced distribution of fruit bearing parts of the tree.

41.3.2 Principles of Training:

• Formation of the mainframe work must be strong. The branches must be suitable spaced apart and the tree must be balanced on all the sides.
• Never allow several branches to grow at one place or very near each other.
• Careful training of main branches is very essential.
• Another important point about training is that if two branches are growing at the same point try to train them to grow at a wider angle. Narrow angle is always weak.

41.3.3 System of Training:

• Central leader system:

In this system the central leader branches are allowed to grow   indefinitely so that it will grow more rapidly and vigorously than the side branches and tree became tall. Such a tree bears fruit more near the top. The lower branches are less vigorous and less fruitful.

• Open centre or vase system:

The main stem is allowed to grow only up to a certain height about 1.5 to 1.8 m and then it cut for development of lateral branches. It allows full sunshine to reach each branch.

• Delayed open centre or modified leader system:

It is intermediate between the above systems. It is developed by first training the tree to the leader type by allowing the central axil to grow un pruned for the first four or five years. Then central stem is headed back and lateral branches are allowed to grow as in the open centre system.

• Bush system:

An unpruned tree multi stem and dwarf growing habit.

• Over head trellis or Bower system:

     When vines are trained on mandap.

• Modified bower or Telephone system:

Similar to bower system except that after every two meter as space is kept to walk and carry out cultural operations.

41.4 SPECIAL HORTICULTURAL PRACTICES FOR INDUCING FRUITING

Of the many factors influencing floral initiation, carbohydrates-nitrogen ration appears to be the one factor that could be controlled. The accumulation of carbohydrates can be brought about by more rapid manufacture and less immediate utilization. In vegetative weak plants, favorable conditions for carbohydrate accumulation will have to be created by provision of desired temperature, light, water and nutrient change while in vigorous plants this change is to be induced by the reduction of water and nutrient supply. Regulation of fruiting can be effected by influencing fruit bud differentiation or by influencing fruit set and development.

Pruning, root pruning, ringing, girdling, notching, bending, smudging are some of the specialized horticultural practices followed for regulation of fruiting.

41.4.1 Ringing and Girdling

Ringing consists of removing a ring of bark about 1 to 2 cm wide around the trunk or branches, while Girdling is a milder treatment to draw a knife around the branch so as to cut through the bark but not the wood. A wire tied very firmly round the stem also serves the same purpose.

Ringing or girdling will increase the concentration of carbohydrates above the wing. It will also reduce the nitrogen supply because subsequent to the stopping of food to the roots, the root growth will be stopped and hence the supply of nitrogen to the tree will slowly decrease and became limited. No more root growth, no nitrogen supplies. The result will be a wide C: N ratio and then flowering increased. Ringing is a drastic operation done when fruit trees fail set fruit. It is likely to check vegetative growth and to some extent the growth of roots. Ringing is done in vigorous mango tree.

       i. Notching

It is similar to ringing except that in notching only soil slip bark about 0.2 to 0.5 cm thick and 1.5 to 2.5 cm in length is removed just above or close to a dormant bud in slantwise so that the latex does not coagulate in the bud itself. The bud selected should be large, plampy and healthy which is produced on a perfect mature wood and has undergone dormancy. Generally 3 to 4 buds in the middle portion of the selected shoot are best to operate on. Fig has responded to notching and it is practiced in fig cultivation. The season for notching the fig is August-September.

       ii. Bending

Bending a branch downward, sometimes checks growth and causes accumulation of starch in the branch with greater flowering. This tends to increase carbohydrate concentration. The bending brings pressure on the bark on the translocation of photosynthesis is obstructed due to narrow passage. The bending of branches is usual as a substitute for severe pruning in shaping the young trees and more fruit is borne because more branches are left to bear and more leaves are left to synthesize food material. In case of bending the effect of apical dominance of the growing shoot is removed and auxins during translocation activate the dormant buds. This is usually practiced with local guava variety in the Maharashtra state (Deccan area).

       iii. Smudging

Smudging is a practice of smoking the tree by burning brush wood on the ground and allowing smoke to pass through the centre of the crown of the tree. The smoking is discontinued as soon as the terminal buds begin to swell. Not commonly followed in India. Practice of smoking to the trees like mango, commonly employed in the Philippines to produce off-season crop. Smoking containing ethylene gas, which is responsible for initiation of flowering.

       iv. Root pruning

Root pruning results in less carbohydrate utilization of the top growth through there is a little more utilization of carbohydrate for root functions. There is an accumulation of carbohydrates due to check of top growth, which results in fruit bud differentiation. As the effect of root pruning is to check the vegetative growth. The plant became dwarf. Root pruning is a method of inducing fruitfulness or determining the time of flowering. The root pruning is done two months before the bloom required. The main roots are exposed to the sun and the fibrous roots are cut, so water is withheld. The trees are allowed to go dry until their leaves wither and fall down. The time taken for leaf fall is from 3-4 weeks. After that exposed roots are covered with a mixture of soil and manure. The trees are then immediately irrigated. First irrigation may be given with very less water. The trees burst into flowering in about 2-3 weeks. Practice very widely adopted by citrus growers in western and central India (in santra). The trees on which root pruning is practiced quite frequently are short lived and are liable to be week and unhealthy. Hence root pruning is usually restored to when other method such as ringing etc. Root pruning is generally included in bahar treatments given to fruit trees like mosambi, santra, guava, pomegranate, lime etc. It is also practiced while manuring large trees like mango, by trench method where smaller roots coming in the trench are usually cut away.

       v. Bahar treatment

This practice is followed with fruit trees like mosambi, santra, grape fruit, guava, pomegranate ber, lime etc. in the state of Maharashtra, M.P. and Gujarat etc. As there is no distinct winter (very cold winter) these fruit trees are usually continuous vegetative growth resulting in indistinct flowering season. This practice is useful in encouraging flowering as well as regulating the time. About 1 to 1 ½ months prior to the expected flowering irrigation is withholding. There are three flowering season namely Mrig bahar, Hasta bahar and Ambe bahar.

    Mrig bahar: Flowering in June-July

    Hasta bahar: Flowering in October-November

   Ambe bahar: flowering in December-February

The orchard is ploughed up to 20 cm depth both ways and the roots are exposed by removing the upper 10-15 cm of soil within a radius of 60-90 cm around the trunk. The dead and decayed fibrous roots are removed in the area exposed. The leaves start turning yellow, shrivel and fall. These are the indication to know that the trees have rested long enough and accumulated food reserves. The exposed roots are then recovered with original soil and necessary manures are added. Trees are irrigated lightly. The second watering is given on the 3^rd or 5^th day and first two watering stimulate blossoming and if heavy irrigations are given at the beginning, this may tend to vegetative growth only. Root exposure is not necessary in case of sandy, sandy loam and other types of light soils. The choice of bahar depends upon availability of water and time of year the fruit is required in the market. Where irrigation water is available, the grower prefers Hasta or Ambe bahar.

41.5 GROWTH REGULATORS

Growth retardants like CCC, (in Mango 1000 ppm.), higher concentration of Auxin, NAA (in Mango 200 ppm), Ethylene -750 ppm, Paclobutrazol -4-6 g (Cultar).

41.5.1 Use of Hormones as Plant Growth Regulators in Horticultural Crops

• What are hormones: Hormones are internally synthesized compound in plants bodies and they markedly affect the metabolic activities inside the plant. They required in very minute quantities.

Since plants make them they are organic in nature, however, they can also be prepared synthetically and such synthetic hormones are also as effective as the organic hormones produced naturally by plants.

• Effectiveness of hormones: Different hormones have regulatory effects on different activities. Further, two derivates of a compound can also have different effects.
• Carriers: The medium in which the hormones are mixed is called carrier. This may be water, alcohol, oil, charcoal powder, talc or flour etc.
• Spreaders: Certain plants have waxy coatings on their bodies. In such cases spreader like soap are mixed with hormones. Spreaders reduce the surface tension and even ensure spreading of the liquid applied.
• Use of hormones -  It is done in following activities:

              i. Rooting of cutting

              ii. Blossom thinning

              iii. Preventing fruit drop

              iv. Increasing fruit setting or development of parthenocarpic fruits

              v. Germination of seeds

              vi. Early maturity

              vii. Weed control

 i. Rooting of cutting: Various chemicals compounds are known to be useful in rooting of cutting e.g. sugars, potassium permanganate, manganese, iron, phosphate etc. carbon monoxide can also be useful in root formation but the most successful are indolebutyrie acid (IBA) and naphthalene acetic acid (NAA). Some new promising hormones are trichlorophenoxyacetic and trichlorophenoxypropionic acid.

These hormones are effective only when used in low concentrations. In high concentration they inhibit growth. Mixture of hormones is more effective than single hormone.

(a) Advantages:

• Percentage of success in rooting increases
• Quicker root formation
• More root and heavier roots
• Lesser time

(b) Limitation: Plants must have natural capacity. Hormones can only help and

     proper environmental condition.

ii. Blossom thinning: Thinning of fruits is the term commonly used for reducing the number of fruits. Thinning does reduce the number of fruits but the remaining fruits become bigger and gain more weight. In excessive bearing, thinning becomes a necessity. In papaya NAA has been reported to be effective for thinning of fruits.

Naphthaleneacetic acid, naphthalenacetymide sodium salts of NAA is most effective. Proper concentration and the stage of flowers are important. Only fully opened but unpollinated flowers will be killed. Any mistake in concentration might loss the entire crop.

iii. Preventing fruit drop: Abscission layer is the cause of fruit drop. This is a corky layer of cells at the base of petiole of the junction of fruit and stalk. Hormones can prevent the formation of abscission layer.

Quality of fruit is not affected. It is not harmful. Naphtaleneacetic acid and its derivatives are the best. If fruits are not picked in time they may become overripe. More work is done on use of hormones for preventing pre harvest drop in apples.

iv. Increasing fruit setting by seedless fruit production: As early as 1909 it was found that water extract of pollen grains when applied to pistil of flowers induced parthenocarpy, N.A.A. are useful. At present the use is limited to glass house crops particularly tomato.

v. Germination of seeds: Not much success has been obtained in increasing germination through hormone treatment.

vi. Controlling flowering: Ethylene and acetylene are used in Hawali and Australia for early flowering in pineapples. Application of NAA (0.006 % spray) is found to reduce maturity period by 2 months in pineapples. In tomato tridobenzoic acid changes leaf buds into flower buds.

vii. Weed control: Poisonous chemicals like arsenic, boron or petroleum compounds can kill weeds but they are dangerous to human life.

41.5.2 Synthetic Hormones: These are superior to chemical poisons.

1. Selective in action
2. Harmless to soil, harmless to man and animals
3. Less expensive and non corrosive
4. Not inflammable
5. Synthetic in nature and required in very low concentration
6. Kill the entire system

e.g. 2-4 Dichlorophenoxyacetic acid (2-4, D), 2-4-5- Trichlorophenoxyacetic acid (2-4-5, T), 2-Methyl-4 Chlorophenoxyacetic acid, Isopropyl-N-Phenylearbamate.

41.5.3 Glossary of Terms

• Auxin: A substance synthesized by a plant and able to influence growth at some point other than the point of synthesis comparable to a hormone in animals.
• Growth regulators: Any substances or physical factor, either external or internal that influences a growth process in a more restricted sense, a substance that influences growth.
• Hormone: A substance synthesized by an animal organism that is able to influence growth at some point other than the point of synthesis comparable to an auxin in plants. Sometimes the term is used in a broad sense to include auxins.

Plant regulators: Are the organic chemical compounds which modify or regulate physiological processes in an appreciable measure in the plants when used in small concentrations. They are readily absorbed and move rapidly through the tissues when applied to different parts of the plants.