TO Sept.. J910.J Spritig Frosts. 599 



■IS not to be feared, since the latent heat liberated counterbalances further 

 loss by radiation. 



A similar liberation of heat takes place on congelation or. in other 

 words, the change into hoar frost of the water first deposited as dew. 

 Hence it is that, even though the temperature may fall sufficiently for 

 there to be a frost, disastrously low temperatures will not be reached if 

 abundant moisture be present. 



White or Black Frosts. 



Thus is explained the well known popular distinction between white 

 and black frosts. In the case of the former, the moisture deposited from 

 the atmosphere, at first in the form of dew, has gradually frozen into the 

 white hoar frost so well known to all. Such frosts are seldom very severe 

 •owing to the liberation of heat during the changes in state of the deposited 

 water referred to abo\e. The general temperature can only fall very 

 gradually and it is rare for it to reach a point sufificiently far below freezing 

 for really grave damage to be done. 



In the ca.se of a black frost, conditions are very different. They can 

 only occur when the air is so dry that there is not sufficient water \apour 

 to condense and thereby check a further fall. If the other conditions 

 permit active radiation there is nothing to hinder the steady fall of tem- 

 perature which may thus reach a disastrously low jioint. although there 

 is practically no outward visible manifestation. 



Indirect Preventive Measures. 



In addition to the obvious course of only selecting as a site for a vine- 

 yard a locality little exposed to frost,* thei'e are several cultural methods 

 by which the vine may be caused to delay coming into leaf for a few- 

 days and in this way damage by frost may often be avoided. These 

 methods may be briefly recalled. 



Selection of Late Budding Sorts. — Different \'ines vary greatly in their 

 susceptibility to frost; late sorts often escape when earlier ones succumb. 

 The severe frost at Mildura in September, 1908, did much damage to 

 the Sultana crop, whereas Zantes and Gordos were practically unharmed. 

 Again, several sorts possess the peculiarity of producing fruit on the 

 laterals thrown out as the result of damage to main buds. 



Late Pruning.— ^y delaying the pruning until the buds are about to 

 burst, sprouting may be delayed a week or even two. which may be suffi- 

 cient to tide over a critical time. This method cannot well be applied 

 to a whole vineyard, but it is always safer to lea^e the pruning of low-lying 

 parts of a vineyard to the last. The provisional pruning practised in many 

 parts of Europe consists in the removal of all useless wood and the leaving 

 of spurs two or three times the required length, at the first pruning. When 

 the buds are about to burst, these can be rapidly shortened back to the 

 length required, the commencement of vegetation being thus almost as 

 effectivelv retarded as by late pruning applied to the whole vine. 



Sometimes extra rods are left on the vine ; the.se are tied vertically until 

 danger of frost is passed. Should no frost occur, they are removed. In 

 case of frost, they bear the crop, the rest of the vine being shortened back. 

 Sometimes, where vines are trained on cordons, the whole of this is tied 

 vertically until danger of frost is past, and afterwards brought to its 

 horizontal nosition. 



• Hillsides are well known to be less frosty than lev -lyingr flats. The niodorating influence of large 

 bodiesof water is cinsiderable ; in northern Victoria vineyards situated close to the Murray Biver art much 

 less liable ti frost than those 10 or 12 miles from it. 



