70 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



regions. The cause of this injury has for the most part been an 

 enigma, but it has been known to occur during that character of 

 weather locally spoken of as " electric" or "Santa Ana," which is in 

 reality a dry condition of the atmosphere caused by the hot dry 

 winds of the desert sweeping through passes in the mountains onto 

 the lower lands adjacent to the ocean. The nights in southern Cali- 

 fornia are usually cool, but during these disturbances from the desert 

 they frequently become very warm. 



Records of fumigation when the temperature was about 65° F. 

 were secured during the autumn of 1909. A part of an orange orchard 

 was treated on three consecutive nights during the so-called " elec- 

 tric" weather, when temperature ranged from 66° F. to 77° F. Con- 

 siderable burning resulted. Work was then stopped for a week until 

 the nights became cooler, when the rest of the orchard was treated. 

 No burning at all occurred. The injury to the fruit during the hot 

 nights consisted of real burns covering much of the fruit — not small 

 pits which are the usual indications of fumigation injury. This burn- 

 ing was exactly of the same character as was produced in a large 

 orchard at Redlands fumigated during the late summer of 1908 on 

 similar warm nights. Records have been secured of burning in other 

 orchards treated under similar weather conditions. 



From the data at hand it appears that injury from fumigation will 

 take place at high temperatures. Based on the author's experiments, 

 it is advised that fumigation be.stopped at a temperature above 65° F. 

 Although in some instances work may be carried on at a slightly 

 higher temperature with impunity, the risk of injury appears to be too 

 great. 



Cold. — During December, 1908, a part of an orange grove at Rivera 

 was fumigated by a private outfit which kept temperature records 

 during its work. At the time the work commenced the temperature 

 was above 40° F. No injury was done until the fourth or fifth set, 

 when the temperature had fallen to 37° F. This set was slightly 

 burned. The next set was badly burned, much fruit dropping. 

 Unfortunately, the temperature for tkis set was not taken. The fol- 

 lowing set, which was the last, was made while the temperature was 

 at 32° F. The tops of many of these trees were severely burned 

 back, while all the fruit on some of them dropped. 



On December 3, 1909, exact records of burning from fumigation 

 were obtained. Three sets were made on this particular night — the 

 first while the temperature reached about 36° F. to 37° F. ; during the 

 second it dropped from 36° F. to 32° F.; while during the third set 

 the temperature reached 31° F. The first set was slightly injured; 

 the second was severely burned and much fruit dropped; while prac- 

 tically all fruit on the third set dropped, and some trees were so 

 severely burned as to lose most of their leaves. 



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