A-pril, '13] YOTHERS: OILS ON CITRUS TREES 163 



After about two weeks it was noticed that the leaves of those trees 

 that had been sprayed were still of a slight yellowish green and those 

 left unsprayed had changed into a dark green. At the end of a month 

 this difference had entirely disappeared, and so far as could be ascer- 

 tained no permanent injury had been done. Although some differ- 

 ence may have existed according to our observations, none could 

 be detected between those leaves sprayed with the distillate which 

 was somewhat volatile and the heavy parafiine oil of 24° Baume, which 

 was very stable. This observation would indicate that the coating 

 of the new leaves with oil spray interfered to a limited extent with 

 the formation of chlorophyll. 



The excessive use of sjDrays may be injurious and some tests were 

 made to determine the accumulated effect of one of the above oils. 

 The same trees were sprayed with the paraffine oil 24° Baume using 

 1| per cent of oil in the spray three times at intervals of six weeks 

 "during the summer, the first application being made May 13, 1911. 

 The effect of these repeated applications was very marked. The 

 leaves were small as compared with those from other trees. There 

 were considerable dead twigs in the trees and the fruit was very small 

 and very late and sour compared with the fruit from adjoining trees. 

 There was no yellowing of the leaves, nor burning of the leaves nor 

 fruit by these applications. The trees sprayed only once on May 

 13 and a check on the above were much improved by the application. 

 It should be stated that a single application of a spray containing 

 1 per cent of the above oil instead of 1| per cent as was used would 

 have been sufficient to eliminate the damage caused by insects. No 

 experiments were conducted to determine the accumulated effect of 

 as weak a dilution as | of 1 per cent of oil but it is the opinion of 

 the writer that such a dilution would not be injurious even though 

 used very frequently. 



The weather conditions which may exist at the time of the appli- 

 cation may be of much importance. It has been known since Hub- 

 bard made his investigations that low temperatures following the 

 application of kerosene emulsion would result in injury. This is 

 due to the low temperatures preventing the evaporation of the kero- 

 sene, thus permitting it to remain for too long a time in contact 

 with the leaves and interfere with their function. Those oils Used 

 in the manufacture of miscible oils as well as the petroleum fuel oil, 

 distillate oil, and the paraffine oils are much less volatile than kerosene 

 and consequently just as liable to cause injury when the application 

 is followed by low temperatures. The author has sprayed thousands 

 of trees and known of other thousands sprayed by other people and 

 only one or two instances are known to him that disastrous results 



