Physiological disorder in Litchi

a) Poor Fruiting/ Non-Fruiting / Irregular Fruiting:

• Caused due to late application of manures and fertilizers (Particularly nitrogenous fertilizers), type of soil coupled, high frequency and heavy irrigation just before the panicle emergence and flowering period.
• Late harvesting and severe pruning and training operations may lead to non-bearing in that particular year of operation.

Management

• On the basis of age of the trees, the commercial orchards should be properly fed with balance nutrition immediately after fruit harvest and irrigation at right time through right method, particularly at aril development stage.
• The plant protection measures to control major pests and diseases should be followed.
• Proper pruning and training at the time of harvesting and just after harvesting is needed, while harvesting of the fruit bunches, the branches having 8-10 inches length should be plucked to give rise strong and healthy flush to bear fruits in next year.
• Late pruning and training should be avoided. The tree should be trained to give canopy shape in a semicircular manner or an open umbrella shape.

b) Flower and Fruit Drop:

• Caused due to failure of fertilization, embryo abortion, nutrition and hormonal imbalance and external factors like high temperature, low humidity and strong westerly winds as well as due to fruit borer and heavy mite attack.
• Studies revealed maximum fruit drop during the first fortnight after fruit set and at harvest the retention varies between 3.0-39.6% among the cultivars.

Management

• High fruit retention in litchi can be ensured by controlling winter shooting, flowering period and flower quality.
• Timely treatment of plants for strong and healthy shoot production delays flowering phase and increases the female flower ratio and finally the fruit setting rate.
• It is advised not to do any type of spray at the blooming stage of the orchard.
• Spraying of ZnSO4 @ 0.2% at 30 days before panicle emergence induces healthy inflorescence leading to more fruit set.
• Foliar application of 0.2% Boron, 2-3 times during the period of fruit growth and development enhance fruit retention, minimize cracking, improve fruit colour, sweetness and enhance maturity leading to increased percentage of quality production.
• Two foliar applications of planofix @ 4 ml/5 litre water may be done at an interval of 15 days from peanut size fruits.
• Treatment with growth regulators like NAA at 20-30 ppm, GA, at 20-25 ppm, 2,4-D at 10-20 ppm are effective in minimizing fruit drop when sprayed on panicles, before the flower opening.
• The fruitlet drop can be reduced by the sprays of ZnSO4 and synthetic auxins like 3,5,6-trichloro-2-pyridyl-oxyacetic acid (3,5,6-TPA) on fruits increasing yield.

c) Fruit Cracking:

• Caused due to varietal characters, orchard soil management, inappropriate levels of water at maturity stage, light, mechanical injuries, temperature and micro-nutrient deficiency.
• Fruit development is affected, particularly the development of the fruit skin, resultantly the cell division is reduced and the fruit skin becomes inelastic, and often splits when the aril grows rapidly before harvest.
• This can occur after irrigation or heavy rain, or just an increase in relative humidity.

Management

• Selection of site is a most effective way to minimize rain drainage of fruit orchard. The appropriate site should be with little or no rain incident at near harvesting time.
• To save the cracking problem at maturity stage, fruit plants may be covered only on the top and permit free air flow into the sides.
• Application of calcium @ 2 m/l liquid formulations and Gibberellins @ 20 ppm, reduces the activity of cellulose and thereby reduced cracking.
• Sprayings of 2,4-D and NAA at concentrations 20 ppm or 20 mg/litre reduces cracking.

d) Sunburn:

• It is a type of direct thermal injury and in case of higher temperature, the tissue coming in contact/exposure gets sunburnt/ sunscalded.
• Lower translocation of calcium in the pericarp region also found to favour sunburn disorder.
• In case of sunburn light brown blotches appear on the portion of the fruit skin facing direct sun rays.
• In severe cases more than half of the surface area becomes discolored, blotchy light brown. The blotches become intense in few days and the blotchy area dries up blocking of the aril growth and finally destroying the market value of the fruit.
• The symptoms appear more on the south west side than the north-east side as on the latter side fruits remain almost in shade except during early hours of the day, which is not harmful.

Management

• Irrigation at regular interval during the fruit growth and ripening stage reduces the sunburn.
• Planting wind break around the orchard provides protection from desiccating hot winds, thereby low sunburn.
• Irrigation through sprinkler system during hot hours increases humidity, cools the orchard atmosphere thus decreases the incidence of sunburn.
• In light and sandy soil only light irrigation with increased frequency (4-5 days interval) is found beneficial.
• Feeding trees with sufficient quantities of organic manures particularly compost, FYM, cakes, green manure, vermi-compost along with applied irrigation at regular interval during fruit development and ripening stage have been found useful.

e) Black Spot:

• It is caused due to deleterious effect of smoke fumes which contain sulphur dioxide, acetylene and carbon dioxide as found in case of mango.
• The first symptom appears as the development of a small etiolated area at the distal end of the fruit against the normal green color of the fruit pericarp, which gradually spreads, turns nearly black and covers the distal end completely.
• The infested fruit show discoloration and overall slow pace of development resulting very poor development of aril, seed, size and color.

Management

a) The disorder can be reduced by applying proper nutrition and irrigation particularly during fruit growth and aril development stage.

b) Spraying with micronutrients like zinc (ZnSO4 @ 0.2%) a month prior to flower panicle initiation and boron (borax @0.2%) during fruit growth stage can reduce the problem.