Frost Protection - UTL Repository

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F R O S T P R O T E C T I O N : F U N D A M E N T A L S , P R A C T I C E A N D E C O N O M I C S
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employees are unemployed, and, because of unemployment, there is less money
in circulation and the local economy suffers. Consequently, considerable effort is
expended to reduce damage.
The cost-effectiveness of frost protection depends on the frequency of
occurrence, cost of the protection method and the value of the crop. Generally,
passive frost protection is easily justified. The cost-effectiveness of active protection
depends on the value of the crop and cost of the method. In this book, both passive
and active methods are discussed, as well as the economics of protection.
HISTORY OF FROST PROTECTION
Frost damage to crops has been a problem for humans since the first crops were
cultivated. Even if all aspects of crop production are well managed, one night of
freezing temperatures can lead to complete crop loss. Except for tropical latitudes,
where temperatures seldom fall below the melting point, damage due to freezing
temperatures is a worldwide problem. Usually, frost damage in subtropical
climates is associated with slow moving cold air masses that may bring 2–4 nights
of 8–10 hours of subzero temperature (Bagdonas, Georg and Gerber, 1978). In
eastern continental locations, damaging events are typically advective, with weak
inversions. In western continental and marine climates, frost events with calm
conditions and stronger inversions are more typical. The damaging events
typically start with advection of cold air followed by a few nights of radiation
frost. In temperate climates, frost periods are shorter in duration and occur more
frequently than in other climates (Bagdonas, Georg and Gerber, 1978).
For deciduous fruit and nut trees, damaging frost events occur mainly in the
spring, but sometimes in the autumn as well. For subtropical fruits, damage to
the crops typically occurs during the winter. In tropical climates, there is
normally no freezing except at higher elevations. Therefore, when tropical crops
are damaged by cold, the temperature is usually above zero. When the damage
occurs at temperatures above 0 °C, it is called “chilling” rather than “freeze”
injury. In temperate climates, damage to grain crops can also occur before
booting, under severe conditions, or to flowers even in mild frosts.
For grain farmers, the main response is to plant crops or varieties that are less
susceptible to damage (e.g. planting spring wheat rather than winter wheat), or
to not plant sensitive crops in the area if damage occurs too frequently. In any
case, the date of planting should be adjusted to the crop, variety and
microclimate. Similarly, if subzero temperatures occur too frequently,
subtropical crops are preferentially grown in regions with less occurrence of
damage. A good example of this is the movement of the citrus industry further
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