DELAYING BLOOM OF FRUIT TREES 497 



Tected " tO SUndse ' the greater the amount of damage that should be 



As a rule, the killing temperature recorded in these experiments oc- 

 n m the mommg, from one to two hours before sunrise. Whenever 

 the killing temperature occurred this late in the morning, and remained 

 below the danger point until sunrise, the injury was great. On the other 

 hand, if the minimum occurred at midnight, or a little later, and then 

 gradually rose to the freezing point, so that the frozen buds, blooms and 

 truits had time to thaw out slowly before sunrise, the injury was in- 

 significant. This was the case April 5, 1910, when at 2:15 A. M the tem- 

 perature was 24M degrees. By 5:30 it had risen to 31 degrees, and the 

 injury done to the Alexander peaches which were in full bloom was 

 estimated at 2 l / 2 %. 



As the young fruit develops it seems to get more tender, until it grows 

 beyond a certain size, when it seems to get hardier again; so that the 

 later frosts which come after the young fruits have made quite a growth 

 are liable to do more injury than the same degree of cold in the earlier 

 part of the season, when the fruits are less developed. At this -stage of 

 growth, 2fr/ 2 to 27 degrees would probably be dangerous to peaches. The 

 very late frost of 25 degrees on May 4, 1912, killed practically all the 

 peaches in the experimental orchard, while 24 degrees on April 17, 1910, 

 left about 30% of the Elbertas. 



On the whole, apples and pears seem to be more resistant than 

 peaches and plums, This was strongly indicated in 1912, when practically 

 all the peach crop was destroyed on May 4, by a temperature of 25 de- 

 grees; while there was a very heavy crop of pears and apples harvested 

 the following fall. 



European and native plums seem to be slightly hardier than Japanese 

 plums and apricots, which are the least resistant of all the fruits included in 

 the test. 



DELAYING BLOOM BY WHITEWASH 



Another suggestion comes from Missouri. It is concerning de- 

 laying activity in deciduous trees by spraying with whitewash to 

 reflect heat the absorption of which by dark bark causes the ac- 

 tivity of the tree to begin. Prof. J. C. Whitten of the University 

 Experiment Station says : 



Purple coloring matter on untreated peach trees often absorbs heat 

 enough on a sunny cold day in winter to raise the temperature of the 

 trees 25 degrees or more above the temperature of the atmosphere. Whit- 

 ened trees remain at atmospheric temperature or usually a degree or so 

 below. 



For ten consecutive years we whitewashed diagonal rows of peach trees 

 across the Experiment Station orchard just before midwinter. In this section 

 we had five general peach crops during that ten years on untreated trees; 

 on whitewashed trees of the same varieties we had eight crops. The five 

 crops on untreated trees were not all full crops; the eight crops on 

 treated trees were all but two full crops. More than double the amount 

 of fruit was secured in ten years on the whitewashed trees. The treated 

 trees were anywhere from a few days up to ten days later in blooming. 

 In years when normal weather prevailed until sudden warm spells brought 

 the trees into bloom hurriedly, there was only a little difference in time 

 of blooming, and under normal conditions there was a week or more 

 difference in their blooming. This is less important, however, than the 

 fact that the whitewashed trees began their first starting into slight growth 

 on sunny days in late winter fully six weeks later than the naked trees. 



The writer is not aware that whitewashing to delay bloom has 

 directly entered into California practice, but it may have had in- 



