INTRODUCTION
The cold season begins over India by early December. During the winter months, under the influence of western disturbances, which are followed by cold dry northern winds the night temperatures fall rapidly by 7-8 degree centigrade below the normal & sometimes more in regions north of the Deccan Plateau & by about 5 degree centigrade in the peninsular parts of the country. The ground temperatures are usually much lower than air temperatures. The crops may be subject to sub-zero temperatures & damage due to chilling or ground frost is likely to take place. The frost hazard is greatest in northern Punjab, being 10-20 days each in December, January & February. Southwards & eastwards of this area, frost occurrence decreases rapidly.

Valleys in which cold air stagnates are subject to frost to a greater extent, especially in the grape fields of Madhya Pradesh & Maharashtra. While laying out orchards & tea-gardens, such valleys should be avoided. Trees planted as shelter belts or as shade-trees protect the crops during the periods of mild frost. When the standard screen temperature is 5-7 degree centigrade, some plant injury is possible even if the stage of ground frost is not reached. Valuable crops can also be protected by covering the ground with suitable material, e.g. paper, plastic or celophane, to reduce the cooling of the ground through radiation.

Several studies indicated that vines obtained from cuttings were more sensitive to low temperatures than those obtained by micropropagation, which indicate that the factors influencing the robustness and frost resistance depend on the agro managerial systems employed.

Smudge pots and other conventional processes utilized to prevent frost damage to orchards experience only limited success, especially when the ambient temperature falls well below freezing for any substantial length of time.

There is a chronic and large demand for low cost, effective and environmentally acceptable cold protection, also referred to as “frost” protection, techniques in temperate areas around the world to protect orchards (pome fruits, stone fruits, nut crops, citrus), vineyards, cut flowers, small fruits (berries), Christmas trees, Douglas fir seed orchards and numerous other crops against damaging cold temperature occurrences.
Protection times include frosts in the spring and fall as well as severe winter freezes.
Cold protection events usually occur during "radiation" frost conditions when the sky
is clear and there is little wind and strong temperature inversions can develop.
These conditions can happen during spring, fall or winter, although most tree crop cold protection activities occur in the spring and are designed to keep buds, flowers and small fruitlets above the "critical" temperatures at which they can be killed.
On the other hand, it is often necessary to frost protect vineyards in the fall to prevent leaf drop so that new sugar will continue to accumulate in the berries.
Sometimes it is required that protection measures be initiated during very cold temperature events during the winter period on perennial tree (i.e., peaches, apricots) and vine crops.
Very often only a couple of degrees rise in air temperature is sufficient to minimize cold damage.