Fruit crops need protection to brave the chill

AK Sangwan, PK Arora and Anil Kumar

IT takes years to grow a fruit tree large enough to help the horticulturalist reap economic dividends. During this period, the tree is exposed to many biotic and abiotic stresses in the form of diseases, insects and weather. Frost is of vital horticultural concern and one of the most destructive problems faced by fruit growers of Punjab in January, when the temperature drops to near-zero or sub-zero levels. It results in substantial losses to the crops of fruits such as kinnow mandarin, kagzi lime, ber, guava, papaya, mango and strawberry. The damage can be of different types, including destruction of branches, foliage, tender twigs, flowering, fruit drop and fruit quality. Nature has its own means to brave weather hostilities. In deciduous plants, it is done by shedding leaves during winter i.e. during the dormant condition, and the evergreen plants withhold their new growth. In the first case, the protection is complete and in the latter it is partial. So the fruit growers must gear up to protect their precious fruit plants from frost. They must plan a strategy to fight it out by following methods and techniques which are usually suitable for most of the fruit crops.

Choose hardy species

There are many hardy fruit tree species which have an intrinsic capacity to tolerate frost e.g. citrus fruit is more tolerant than mango, aonla, papaya etc. Even among the citrus fruits, the mandarin types are the most cold-hardy, followed by sweet orange and grape fruit. Lemons and limes are the least cold-hardy and some mango varieties such as langra, malta, safeda and fazri are more important than the other susceptible varieties. But even the hardiest fruit can be hit by sudden drops in temperature or a long cold spell, for instance, chilling injury and fruit drop in kinnow mandarin at maturity during January.

Maintain plant health

Healthy plants are supposed to fight the frost better than the weak ones. Optimum and timely application of manures and fertilisers, depending upon the age of plants, and irrigating the plants at crucial stages are key factors to maintain good plant vigour. Protecting the plants from insect-pests and diseases attacks by following the recommended spray schedules for each pest species throughout the year will also help to keep the plant healthy enough to tolerate the frost better.

Windbreaks

Chilly winds during the winter are very harmful and lead to damage to the fruit plants. Any mechanical barrier, maybe in the form of trees, straw or hedges, makes an effective windbreak and protects the plants. Always plant windbreaks on the windward side of the orchard well before the latter is established; it ensures protection from the cold wave. Single or double row of tall and small trees planted alternately around the orchard form a thick wall and reduce the impact of frosty winds on fruit plants. Eucalyptus, jamun, seedling mango, arjuna and mulberry are ideal windbreak plants. In the spaces between windbreak trees, a hedge of bougainvillea, jati khatti, galgal or karonda can also be used. However, avoid the hedge of citrus species around the citrus orchard.

Pruning of plants

Well-trained low-headed trees withstand the cold better than tall and improperly trained fruit plants. So, it is very important to train fruit trees as per the recommendation for the region. Training refers to the physical techniques that control the size, shape and direction of plant growth. Pruning should begin as late in the winter as possible to avoid winter injury. To minimise the potential for winter injury, summer pruning should not be done after the end of July.

Moisture factor

Make sure that the soil around the tree root zone is wet. This keeps the soil warmer than the dry area and protects the roots from cold injury. It is one of the most common practices followed by the fruit growers to combat frost effectively. By irrigating the orchards during the winter, it is possible to raise the temperature by 1-2°C, thus it is one of the most economical and practical methods to protect from frost. It is desirable to maintain the orchard moisture level whenever there is a forecast of frost or during a prolonged cold spell.

Smokescreen

Create a cloud of smoke in the orchard by burning the waste material at four to five points in the night to form a homogenous cloud whenever frost is likely to occur. It helps to minimise the frost damage in two ways. Firstly, the smoke forms a screen over the plants, thus warding off the frost. Secondly, it raises the temperature of the orchard to some extent. However, its effectiveness is reduced when the wind blows.

Covering with thatches

Cover the young and newly planted fruit plants with thatches or kullies made of sarkanda or other farm waste material such as sugarcane trash, paddy straw and maize stalk to shield the tender plants from the chilly winds. Care should be taken that the southwest side of the plant remains open to allow sufficient sunlight and air needed by it for its growth.

Mulching

The insulating properties of mulches help to keep the soil cooler during the summer and warmer in the winter. Mulching in the winter is a critical tool for gardeners to protect plants from freezing conditions. The soil under the mulch doesn’t freeze, and that allows the plants to absorb more water. It is a standard form of winter protection for many shallow-rooted plants.

Minimising frost damage

Fruit plants, especially papaya, banana, mango, litchi, amla and guava, should be protected from frost.

Papaya is a tropical fruit plant. It requires warm and humid climate and can be cultivated up to a height of 1,000 metres above sea level.

It can be grown successfully in Punjab and plains of north India. Papaya is very sensitive to frost and wet soil conditions. It should be planted in frost-free areas on well drained soils. Young plants must be well protected from frost. They should be covered with transparent plastic envelopes, sarkanda, straw thatches or other covering material from November to February.

Amla is hardy and can be grown in variable agro-climatic and soil conditions. The mature tree can tolerate temperature up to 46°C and young plants need to be saved from frost during winter. It is a potential crop for degraded and marginal soils having soil pH 6 to 9.5.

Amla, also known as Amrit phal, is used in indigenous medicines.

Source: PAU Package of Practices for Cultivation of Fruits

The authors are on the faculty of the PAU’s Regional Research Station, Abohar

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