Litchi suffers from two types of physiological disorders:
Disorder # 1. Fruit Cracking:
Cracking of fruits is the main stumbling block in the expansion of litchi cultivation in other parts of India. Since, the cracked fruits rot quickly and are not worth marketing, the growers are put to great financial loss. In extremely hot season the loss is about 50% of the net gain.
The important reasons of fruit cracking in litchi are:
i. Alternative spells of humid conditions (aggravated by rains) and dry heat in summer causes cracking and drop of fruits.
ii. The fruits split when dry and desiccating winds blow during the later period of their growth. Extremely hot sunny days cause sun-burn injuries to the fruits, which can be noticed as dark necrotic patches on the fruit skin. As the burnt area of the skin fails to stretch along with its remaining portion at the time of aril enlargement, a split occurs.
iii. Hail storms during active fruit development also cause injury on the fruit skin which subsequently ruptures.
iv. Cracking is also caused by high internal hydrostatic pressure generated during rainfall. Ripe fruits have high osmotic potential and absorb water rapidly if they remain wet with the rain. It results the expansion of inner tissue which leads to splitting unless the skin can stretch sufficiently or can withstand the stress.
v. The early varieties like Shahi are more prone to cracking than the late ones like China.
Some remedial measures have been found quite effective in checking or minimising the cracking loss in litchi fruits:
i. Irrigate trees weekly or fortnightly during growth period of the fruits.
ii. Flood the orchards frequently during the early summer to increase humidity.
iii. Spray the fruit panicles with 25 ppm NAA at fort nightly intervals from fruit set till harvest.
iv. In the early stage spray the fruit panicles with 0.4% boron.
Disorder # 2. Fruit Drop:
Although, fruit drop is not a serious problem in litchi, yet growers have to face a great deal of loss due to fruit drop at different stages of growth and development.
Maximum fruit drop occurs during second and third week after fruit set. Fruit drop is varietal character too. The variety Calcutta Late bears, the highest number of fruits. I to maturity while Dehradun the least. Apart from the I competition among fruits for water and nutrients, strong I winds significantly increase the fruit drop.