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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damage that occurs in some years. This is also true for spot damage on deciduous
fruit damage during autumn freezes. The wet-bulb temperature is always between
the air and dew-point temperatures and the wet-bulb temperature is lower when
the dew-point is low. If the fruit is wet going into a freeze night, protection should
be started as early as possible. In these conditions, the objective is to evaporate the
water off the fruit before the wet-bulb temperature reaches 0 °C. Using heaters
or wind machines before nightfall will help to evaporate water off the plants.
However, using wind machines when the fruit is wet after the wet-bulb
temperature falls below the critical fruit damage could cause rind injury or worse.
Table 4.11 gives the air temperature corresponding to a wet-bulb temperature
T w = 0 °C for a range of dew-point temperatures and elevations.
TABLE 4.11
Air temperatures (°C) corresponding to a wet-bulb temperature T w = 0 °C for a
range of dew-point temperatures and elevations
DEW-POINT TEMPERATURE
(°C)
0
-2
-4
-6
-8
-10
-12
-14
ELEVATION (METRES ABOVE MEAN SEA LEVEL)
0 m 500 m 1000 m 1500 m
0.0
1.2
2.3
3.3
4.1
4.8
5.4
6.0
0.0
1.3
2.5
3.5
4.4
5.1
5.8
6.3
0.0
1.4
2.6
3.7
4.6
5.4
6.1
6.7
0.0
1.5
2.8
3.9
4.9
5.8
6.5
7.1
-16
6.4
6.8
7.2
7.7
-18
6.8
7.2
7.7
8.1
90