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Unfruitfulness is a major problem in many fruit crops and their varieties result in huge loss to growers and make fruit cultivation less profitable. Unfruitfulness in fruit crops refers to the state where the plants not capable of flowering and bearing fruit.
Causes:-
A.Environmental causes:
1) Some varieties of a fruit crop don‘t flower in a locality owing to undetermined environmental factors eg. several varieties of mango have not flowered in Nepal. This can be remedied by top working with other varieties.
2) Unfavourable temperature may cause failure of any flowering as in the case of apples in conoor due to lack of sufficient winter chilling. It has been remedied to certain extent by oil emulsion sprays and DNOC (Di-nitro-ortho cresol).
3) In tropics, plants flowering in summer may experience retarded pollen germination due to high temperatures and low humidity. The provision of windbreaks, close planting and cover cropping help in improving the situation.
4) Reduced illumination due to close planting ,over crowding of branches or shade will often reduced flowering Thinning out some trees to increase spacing,pruning trees to reduce over crowding and removal of shade can meet the situation.
5) When long day plants of northern latitudes don‘t flower owing to the absence of the critical length of day, they can be made to flower by providing artificial light.On an orchard scale such treatments are not practicable.
6) Late rains may prolong the vegetative growth and delay or reduce flowering in mango. It can be remedied by drying out the soil by deep ploughing and probably by artificial inhibition of growth by growth regulators.
7) Heavy rains may restrict pollinator activity, wash away pollen and prevent pollen germination. Choice of varieties which don‘t flower at such periods of the year is the best way out. In crops like grapes, the pruning time may be altered to avoid the onset of flowering during the period of the rainy season crop may altogether be avoided by hard pruning.
B.Nutritional Causes:
1)Heavy nitrogenous manuring at the time of flower bud initiation often reduces flowering by promoting vegetative differentiation. The practice should be given up. Root pruning and restricted irrigation may be helpful in reducing vegetative vigour and inducing formation of male flowers.
2)Over bearing in the previous season exhausts the tree and reduces subsequent flowering as in mango and most biennial bearing trees. A complete manure mixture applied at the growth flush following the harvest will be helpful (June manuring in mango).
3)Lack of nutrition as in weak shoots causes fall of flowers before and after fruit set. A spray of urea after fruit set will help the development of fruits.
4)Lack of sufficient reserves of carbohydrates in shoots may cause sparse flowering and poor set (shoot bunches of grapes).Ringing and girdling may help. But it should not be continued as a regular orchard practice.
5)Adverse growth features like water suckers will result in a drain on the tree and reduce flowering not only on themselves but also on other branches of the tree.Such shoots arise when big branches are pruned. Then it is necessary to cut big limbs, they should always be set to a strong lateral but not stimulate a dormant bud. Late irrigation following a long drought may cause the production of water shoots .The first irrigation after a drought should always be sparing later ones being more liberal .When water suckers are formed due what ever reason, they should be promptly removed.
6)Deficiencies of elements are sure cause of reduced flowering as well as set. A composite mineral spray at flush time will usually be very helpful. If deficiency is due to alkalinity of the soil, suitable reclamation measures should be adopted.
7)Heavy manuring and severe pruning during the pre-bearing period will prolong it. Pruning should be done while branches are young, preferably by rubbing of axillary buds themselves by frequent observation of the plants.
Seedlings and some species of plants have a long prebearing period during which no undue anxiety should be felt for hastening flowering.
Old trees suffer from inadequate nutrition especially when they are neglected. The short extension of shoots, small leaves showing various deficiencies, scanty leaves and die back of shoots indicate approaching death.
3) In tropics, plants flowering in summer may experience retarded pollen germination due to high temperatures and low humidity. The provision of windbreaks, close planting and cover cropping help in improving the situation.
4) Reduced illumination due to close planting ,over crowding of branches or shade will often reduced flowering Thinning out some trees to increase spacing,pruning trees to reduce over crowding and removal of shade can meet the situation.
5) When long day plants of northern latitudes don‘t flower owing to the absence of the critical length of day, they can be made to flower by providing artificial light.On an orchard scale such treatments are not practicable.
6) Late rains may prolong the vegetative growth and delay or reduce flowering in mango. It can be remedied by drying out the soil by deep ploughing and probably by artificial inhibition of growth by growth regulators.
7) Heavy rains may restrict pollinator activity, wash away pollen and prevent pollen germination. Choice of varieties which don‘t flower at such periods of the year is the best way out. In crops like grapes, the pruning time may be altered to avoid the onset of flowering during the period of the rainy season crop may altogether be avoided by hard pruning.
B.Nutritional Causes:
1)Heavy nitrogenous manuring at the time of flower bud initiation often reduces flowering by promoting vegetative differentiation. The practice should be given up. Root pruning and restricted irrigation may be helpful in reducing vegetative vigour and inducing formation of male flowers.
2)Over bearing in the previous season exhausts the tree and reduces subsequent flowering as in mango and most biennial bearing trees. A complete manure mixture applied at the growth flush following the harvest will be helpful (June manuring in mango).
3)Lack of nutrition as in weak shoots causes fall of flowers before and after fruit set. A spray of urea after fruit set will help the development of fruits.
4)Lack of sufficient reserves of carbohydrates in shoots may cause sparse flowering and poor set (shoot bunches of grapes).Ringing and girdling may help. But it should not be continued as a regular orchard practice.
5)Adverse growth features like water suckers will result in a drain on the tree and reduce flowering not only on themselves but also on other branches of the tree.Such shoots arise when big branches are pruned. Then it is necessary to cut big limbs, they should always be set to a strong lateral but not stimulate a dormant bud. Late irrigation following a long drought may cause the production of water shoots .The first irrigation after a drought should always be sparing later ones being more liberal .When water suckers are formed due what ever reason, they should be promptly removed.
6)Deficiencies of elements are sure cause of reduced flowering as well as set. A composite mineral spray at flush time will usually be very helpful. If deficiency is due to alkalinity of the soil, suitable reclamation measures should be adopted.
7)Heavy manuring and severe pruning during the pre-bearing period will prolong it. Pruning should be done while branches are young, preferably by rubbing of axillary buds themselves by frequent observation of the plants.
Seedlings and some species of plants have a long prebearing period during which no undue anxiety should be felt for hastening flowering.
Old trees suffer from inadequate nutrition especially when they are neglected. The short extension of shoots, small leaves showing various deficiencies, scanty leaves and die back of shoots indicate approaching death.
Such trees may be given one chance to bear by
(1) manuring them heavily with a complete mixture of nutrients
(2) pruning hard up to 3-4 year old wood and
(3) spraying a composite mineral mixture on young flush. Irrigate frequently and protect them from pests and diseases. This may rejuvenate the tree for a few years.
C.Inherent Causes:
1)Low proportion of female or perfect flowers as in some varieties of mango (Jehangir, Allampur baneshan etc.) often is the cause for a poor crop. There appears to be no remedy for this defect.
2)Structural features like hetero styly and habits like dicho-gamy some times restrict the availability of pollen and pollination. The presence of sufficient population of the tress and pollinators ordinarily ensures good pollination and set.
3)Inadequate quantities of pollen appear to reduce fruit set in some varieties of strawberry and some varieties of grape. Use of suitable growth regulators to get fruit setting will circumvent the difficulty.
4)Many varieties of Japanese plums and apples are self sterile. Many other fruits also partially self sterile .So planting varieties which make them fertile with their pollen will solve the problem.
5)When inter sterility is the cause for low fruit set compatible pollenizers have to be provided. Mixed pollen sprays and use of synthetic growth regulators may also be helpful.
6)Triploidy and distant cross are often reasons for low fruit set. Chemical aids can get over the problem.
7)Defects of ovule development, embryo abortion etc.are observed in dropped flowers. These largely seem to be varietal characteristics and cannot largely be altered.
4.Bio-logical causes:
1)Absence of pollinating agents can be a reason for low fruit set in several fruits.Rearing bee colonies in orchards, besides being a subsidiary source of income greatly helps fruit set.
2)When specific insects‘ symbiotic adaptations (like the blastophaga for fig)concerned with the pollination, they must be reared (by growing Capri fig trees in this case). A wooden needle seems to perform the duties of the blastophaga quite as efficiently in promoting set of fig fruit.
3)Pests like the mango hopper which directly attacks the flowers obviously reduce the fruit set. Others which feed on leaves reduce the photosynthetic surface impair production of carbohydrates and thus reduce flowering. Several fungal diseases do the same thing; Suitable remedial measures should betaken to protect the tress.
1)Low proportion of female or perfect flowers as in some varieties of mango (Jehangir, Allampur baneshan etc.) often is the cause for a poor crop. There appears to be no remedy for this defect.
2)Structural features like hetero styly and habits like dicho-gamy some times restrict the availability of pollen and pollination. The presence of sufficient population of the tress and pollinators ordinarily ensures good pollination and set.
3)Inadequate quantities of pollen appear to reduce fruit set in some varieties of strawberry and some varieties of grape. Use of suitable growth regulators to get fruit setting will circumvent the difficulty.
4)Many varieties of Japanese plums and apples are self sterile. Many other fruits also partially self sterile .So planting varieties which make them fertile with their pollen will solve the problem.
5)When inter sterility is the cause for low fruit set compatible pollenizers have to be provided. Mixed pollen sprays and use of synthetic growth regulators may also be helpful.
6)Triploidy and distant cross are often reasons for low fruit set. Chemical aids can get over the problem.
7)Defects of ovule development, embryo abortion etc.are observed in dropped flowers. These largely seem to be varietal characteristics and cannot largely be altered.
4.Bio-logical causes:
1)Absence of pollinating agents can be a reason for low fruit set in several fruits.Rearing bee colonies in orchards, besides being a subsidiary source of income greatly helps fruit set.
2)When specific insects‘ symbiotic adaptations (like the blastophaga for fig)concerned with the pollination, they must be reared (by growing Capri fig trees in this case). A wooden needle seems to perform the duties of the blastophaga quite as efficiently in promoting set of fig fruit.
3)Pests like the mango hopper which directly attacks the flowers obviously reduce the fruit set. Others which feed on leaves reduce the photosynthetic surface impair production of carbohydrates and thus reduce flowering. Several fungal diseases do the same thing; Suitable remedial measures should betaken to protect the tress.
5.Cultural causes:
1)The commonest cause of poor flowering in house gardens is excessive irrigation which restricts aeration of roots and causes sickly symptoms.Increase of intervals of irrigation and provision of drainage are the remedies.
2)Weeds and inter crops may compete with the main crop for nutrition and water in low rainfall areas .Removal of weeds and adequate manuring to meet the demands of both the fruit crop as well as the inter crops are helpful. Inter crops which clash with the irrigational and manurial requirements of fruit crops both in respect of quality and time of application should be avoided.
3)Ploughing or deep cultivation at flowering time will result in drop of flowers and should be avoided.
4)Severe pruning of large limbs which encourages production of water shoots should be avoided. If it is absolutely essential, the branches may be cut to a strong lateral. Wrong pruning techniques may also cause reduction of flowering.
1)The commonest cause of poor flowering in house gardens is excessive irrigation which restricts aeration of roots and causes sickly symptoms.Increase of intervals of irrigation and provision of drainage are the remedies.
2)Weeds and inter crops may compete with the main crop for nutrition and water in low rainfall areas .Removal of weeds and adequate manuring to meet the demands of both the fruit crop as well as the inter crops are helpful. Inter crops which clash with the irrigational and manurial requirements of fruit crops both in respect of quality and time of application should be avoided.
3)Ploughing or deep cultivation at flowering time will result in drop of flowers and should be avoided.
4)Severe pruning of large limbs which encourages production of water shoots should be avoided. If it is absolutely essential, the branches may be cut to a strong lateral. Wrong pruning techniques may also cause reduction of flowering.
The following points should be borne in mind
(1) the pruning should be with regard to bearing habit of the fruit tree,
(2) the pruning should be up to some fruitful buds (in grapes).Harder or light pruning will reduce fruiting,
(3) a balance of vegetative and fruiting wood should be maintained in plants bearing on past seasons wood,
(4) pruning should not be delayed till the new growth is resumed.
In practice good drainage, timely irrigation, manuring and culture and selection of suitable varieties will ensure good set of crops.
In practice good drainage, timely irrigation, manuring and culture and selection of suitable varieties will ensure good set of crops.