The problem of heavy fruit drop in ber is of great concern to the ber growers. Premature fruit drop of about 50 per cent produce is the major problem in ‘Umran’ cultivar which adversely affects the yield and profit of the growers. It is estimated that only 20 – 30 percent fruits attained marketable size of 25 – 30 g per fruit. The ber crop produced only 8-9 per cent fruits which could reach full maturity.
The different types of fruit drop occurred in ber are as follow:
1. Physiological Fruit Drop:
It might be attributed to two main reasons. Firstly, it may occur due to abortion of embryo. During the early stage, the drop is mainly due to shriveling of fruits which occurred up to December. Out of the total dropped fruits 30 per cent has aborted embryo. Secondly, a pre-mature fruit drop may occur due to premature formation of an abscission layer in the stalk of ripe or nearly ripe fruit.
This abscission has been reported to occur as a result of natural exhaustion of growth regulators present in the fruit or when they cease to flow from their production center because of some disorders in the tree or climatic conditions.
The maximum fruit drop was recorded from first week of November to end January which account for 60 per cent of the total fruit set. During this period, the mean temperature decline from 19°C to 10.6°C in January and RH increased from 65 per cent in November to 81 per cent in February. From first week of February to mid-March, the per cent drop decreased and only 17.7 per cent fruits dropped.
The ber fruit ‘Umran’ require 24-26 weeks (180 days) from the time of setting to reach the stage of maturity. The growth is most active during the first six and last twelve weeks but is slow during the middle six weeks. The synthesis of auxin and gibberellin decreased during the slow growth period due to formation of inhibitors.
The deficiency of promoters leads to the formation of abscission layer and cause heavy drop during slow period of fruit growth. Auxins inhibit abscission of fruits by preventing physiological break down of calcium pectate of middle lamella. Spray application of 20 – 30 ppm NAA once in the second fort night of October and again in the second fortnight of November check 10 per cent fruit drop in Umran ber.
2. Drop due to Climatic Factors:
Sometimes severe cold occurs in the month of December which persists for longtime and continues even up to end January. This condition further deepens when cold waves blow. This leads to heavy leaf fall and fruit drop. Heavy reduction in leaves and leading to sparse foliage results into poor photosynthetic activity in plants. The leaves fails to provide the required amount of food substance, thus, fruits stops in growth, shriveled and falls.
To avoid such conditions, apply light irrigation to the ber orchards as and when there is chances of occurrence of frost/cold. Heaps of dried leaves should be allowed to burn slowly to provide a thick smoke screen over the field, which helps in raising the atmospheric temperature. This can save to some extent the heavy drop that occurs during December – January.
3. Drop due to White Ant Attack:
White ant is a major problem in ber orchards. It attacks the root system, on the main trunk and main limbs. This blocks the smooth flow of sap in xylem and phloem. Ultimately there is reduction in supply of available carbohydrates to the fruits and results into fruit drop.
Apply chlorpyriphos to tree basin @ 1 ml in litre of water once in April again after rainy season in September. Prepare thick solution of chlorpyriphos (100 ml in 1 litre of water and apply this solution with the help of brush in the form of paint to the trunk and main limbs after scrapping the affected portion.
4. Pathological Fruit Drop:
Due to attack of fungus (powdery mildew), white powdery mass deposits on fruits and underside of the leaves. The fruits become cankered, corked, disfigured and de-shapened. Such fruits drop heavily before reaching maturity. Spray the affected plants with 0.05% Karathane or Bayleton at flowering, mid-October, mid-November and mid-December to check the disease and subsequently fruit drop.