In this article we will discuss about the adverse effects of high and low temperature on fruit plants in India.
1. Adverse Effects of High Temperature:
The fruit trees, especially the young plants, need much more attention and adequate protection against the hot and scorching weather in May-June. The tolerance of the fruit plants to withstand high temperature varies greatly with species. The fruit plants like those of mango, litchi, citrus, etc. are liable to damage from hot weather as compared with other fruit plants.
High temperature during the growing and rest period causes injuries like:
i. Sunburn and
ii. Sunscald.
i. Sunburn:
The excessive heat during the growing season often results in the burning of leaves and fruits. During the day, branches, leaves, fruits and stem portions which are exposed to the sun become much hotter than the atmosphere and are subjected to sunburn injuries.
The transpiration losses are also much higher at that time. The bark of the affected trunks and branches may crack or peel off in long strips in extreme cases. Such damage to the bark may result in the eventual death of trees or they may get crippled.
ii. Sunscald:
The hot intense sun rays fall on the exposed parts of the tree facing southwest side, resulting into sunscald injuries. The hot sun also scorches the developing fruits, especially those of citrus. The affected portions of the fruits first turn yellow, then brown on further scorching and later even turn black.
Such fruits cease to grow from the affected side, whereas the growth on the other side continues as usual. The fruits thus become malformed and misshapen. The peel of such fruits clings to the segments, which becomes woody and dry. Such defective cull and deformed fruits do not fetch good prices in the market, as their quality is very poor.
Protection against Hot Weather:
The following measures should be adopted to save the fruit trees from sun injuries and adverse effects of hot weather:
i. White-Washing:
This is the most practical method for saving the trunks of fruit trees from sun injury. The lower bare trunk portions of the fruit trees should be white-washed during April. White-washing may have to be repeated in June-July if it gets faded or is washed out by rains. In the white-wash material, little amount of copper sulphate should be added as it helps in warding off the fungal diseases.
ii. Providing Shelters:
Young fruit plants of tender type can be conveniently protected by erecting thatches or Kullies made of Sarkanda, parali (Rice straw) or Khajoor leaves (Date-palm) over them. Quick-growing temporary shade plants like those of Jantar and Arhar planted around the basins provide shade and thus minimise sunburn injury.
iii. Wrapping of Bare Trunks:
Wrapping of lower portions of the trunks of fruit trees with old gunny bags or some other farm-waste materials like parali (Rice straw) or sugarcane trash (Khori) is also very desirable practice, especially in case of young fruit plants of tender type.
iv. Low-Headed Trees:
The plants trained to low-headed framework escape the ill-effects of the hot sun better than the high headed trees. It is, therefore, desirable that the fruit trees should be trained to develop low heads, especially in the hot and arid tracts.
v. Windbreaks:
By growing windbreaks on the western side of the orchards, damage by hot winds can be avoided. The windbreaks should be planted before the planting of the fruit trees. Eucalyptus, mango seedlings, jamun seedlings, arjan, shisham, mulberry, etc. are suitable windbreaks.
vi. Frequent Irrigation:
Irrigation at regular intervals is quite effective against the hot weather and sun injury. The frequency of irrigation should be increased during the hot period (May-June) when desiccating winds generally blow, especially in the arid and hot regions.
2. Adverse Effects of Low Temperature:
December and January are the coolest months in Northern plains when the frosts are commonly experienced. Sometimes frost may also occur in February. Both early and late frosts are more dangerous and inflict heavy damages in killing foliage, twigs, branches, flowers, etc., especially in the orchards which are not properly protected against this hazard. The evergreen fruit trees like papaya, mango, litchi, citrus, guava, etc. are highly susceptible to cold injury under North Indian conditions.
Sometimes even grown-up trees may be affected badly, when the incidence of frost is severe, especially in the frost-prone localities. The newly planted evergreen fruit plants and young plants are much more susceptible to frost damage than the old and well-established fruit trees. The old and well-established fruit trees in healthy condition may, however, escape frost damage.
Weak and sickly plants and those suffering from malnutrition are more prone to frost injury than healthy and vigorous plants. The fruit trees which continue their growth during the winter season due to continued watering and late application of nitrogenous fertilizers, suffer much more from frost than those which have ceased their growth and have entered into dormancy.
Due to the adverse effect of low temperature, different types of injuries have been reported:
i. Black Heart:
In this injury the inner wood is darkened while the cambium and the bark remain alive. The growth of the tree continues and recovers from the injury. Mostly the nursery plants are susceptible to black heart injury.
ii. Collar Injury:
In this injury the damage by frost is usually caused at the ground level. The bark of stem of young trees is killed and cracks appear at the ground level. The inner sap carrying tissues are ruptured through freezing. The injury may also extend down to the roots. Under such conditions, dead bark should be removed and wounds painted to prevent entrance of water or fungi. Bridge grafting is followed to keep the plants healthy.
iii. Crotch Injury:
The injury is specified when tissues are killed in the crotches or fork of both large and small branches.
iv. Splitting of Bark:
It is caused by severe occurrence of frost. The injury may extend to the entire length of the trunk or branches under severe conditions.
v. Killing Back of Shoot and Young Branches:
The sub-tropical and tropical fruit trees may be damaged by frost in early spring. The bark along the cambium layer become discoloured or killed very often. In such cases, normal growth cannot be resumed for a considerable time. With this injury the flowers in mango may be killed and even fruits may be injured in papaya and citrus.
Protection against Cold:
The following measures of permanent and temporary nature should be adopted for protecting the orchards from the frost injury:
i. Permanent Measures:
a. Planting Frost-Tolerant Kinds:
In the localities, where frost incidence is more common, plant only those kinds and varieties of fruits which can withstand frost damage. It is advisable to plant frost-resistant deciduous fruits in such localities like pears, peaches, almond, plums, grapes, etc. or plant relatively more tolerant evergreen plants like kinnow, loquat, ber, guava, etc.
Among the citrus fruits the tolerance is in the following descending order – mandarin, sour orange, sweet orange, grapefruit, gal gal, sweet lime and kagzi lime. Therefore, kagzi lime needs greater protection from cold than the other citrus species.
b. Planting Windbreak:
Always plants windbreaks on the north-western sides of the orchard, which afford protection from the cold waves during the winter season. The ideal windbreak plants are Eucalyptus, mango seedling, ber, arjan, shisham, mulberry and karonda etc.
c. Healthy Trees:
Healthy trees can withstand frost damage much more effectively than weak and sickly plants. The fruit trees may be kept healthy by adopting proper cultural practices and plant protection measures.
ii. Temporary Measures:
a. Training of Plants:
Well-trained, low-headed trees withstand cold better than tall and improperly trained trees. So, it is very important to train young fruit trees properly.
b. Covering with Thatches:
The young trees, as well as the newly planted fruit trees, should be covered with thatches or Kullies made of sarkanda and farm-waste materials like sugarcane trash, rice parali, maize stalk, etc. The south-west side should be left open to allow sufficient sunlight.
c. Wrapping of Trunk:
The exposed portions of the lower trunk of the young plants should be wrapped with old gunny cloth to avoid damage to bark by cold injury.
d. Providing Smoke Screens:
The heaps of dry leaves, grass or trash should be kept ready in the orchard at several places. As and when a frost is threatened or imminent, these heaps should be ignited and allowed to burn slowly. The fire and smoke raises the atmospheric temperature of the orchard by a few degrees and thus the fruit trees are saved from the frost injury.
e. Irrigation:
By irrigating the orchards during winter, it is possible to raise the temperature by 1°-2°C. This is one of the most easy and the most practical method to ward off frost. It is, therefore, desirable to irrigate the orchard during cold spell period.
In horticulturally advanced countries, oil lamps are installed at several places and these are ignited when there is a forecast of the occurrence of frost. Wind machines have also been installed. These are commissioned as and when needed. Violent movement of wind helps to keep away the frost.
Above all, the growers should remain alert and vigilant and keep in touch with the weather forecasts or frost warnings by Radio and TV. The growers should install thermometers in their orchards for knowing fall in temperature. When the temperature falls around 0°C and the atmosphere is still and sky is clear, the frost is sure to occur. At that time, measures like light watering, burning farm-waste materials, etc., may be resorted-to promptly.