External Factors for Unfruitfulness
1. Nutrient Supply:
Application of manures and fertilizers to the tree bearing emergence of flower is generally believed to favour fruit set. Although heavy nitrogenous manuring will stimulate vegetative growth, over bearing previous season exhaust the tree and educe subsequent flowering. Loss of nutrition in a weak shoots causes fall of slower before and after fruit set.
Light, temperature, rainfall, humidity and wind are the major factors which favour fruit set or other wise results in unfruitfulness.
High temperature at flowering will dry up the stigmatic fluid and prevent pollination.
Reduced illumination due to close spacing, over crowing of branches or shade will often reduce flowering.
Heavy rains at blossoming may result into poor fruit set due to washing away of pollens and there by restricting pollinator activity. Flowers of mango are especially sensitive to fog rain and cloudy weather. Cloudy weather and rain are responsible for destroying blossom and newly set fruits of grape vine.
High wind velocity may results into shedding of flowers and fruits.
3. Pest and Diseases:
Attack of pest and diseases adversely affect fruit set. Mango hopper and citrus psyalla suck the cell sap from mango and Santra flowers respectively causing them to shed.
A variety suitable for one locality may not suit for another locality and thus may lead to unfruitfulness.
5. Disturbed water Relations:
Moisture deficit created at a critical stage of flowering and fruit set will result into low fruit set.
6. Cultural Practices:
Deep ploughing at flowering stage, excessive irrigation growing of weeds etc. may result in shedding of fruits.
Pruning induces the fruit set in grape, fig and rose.