254 KEroUT Ul-' OITICE of EX^ElilME^;T iSTATIONS. 



trees in full loaf without iimcli iiijurv, hut niixturos cvon of lower 

 percenta<2:e are liahle to (huna<;e stone fruits under the same condi- 

 tions. Such dilute uiixtures, however, ai)pear to he of no insi^cti- 

 cidjil value except against un})rotected scale insects. A good (juality 

 of kerosene nniy he ai)|)lied to large healthy ])ear and apple trees 

 while they are dormant witiiout injury, hut such is not the case after 

 growth hegins in the sj)ring. Stone fruits, on the contrary, hehave 

 quite dirt'erently, since dormant trees are injured in dilute mixtures, 

 while kerosene nniy he applied even undiluted to peach trees while 

 the huds are swelling. It is recommended as a safe procedure to 

 spray peach and plum trees with a 25 per cent mechanical mixture of 

 crude petroleum after the buds begin to swell, but the same treatinent 

 applied to dormant trees Avill injure or kill them. The New York 

 State Station considers it unsafe to treat pear or apple trees with 

 crude petroleum after the buds have begun to swell. 



In a test of a proprietary soluble petroleum compound at the Vir- 

 ginia Station" it Avas found that a 10 per cent solution applied while 

 the trees were in leaf destroyed all the foliage on young a^jple trees 

 and from 40 to 50 per cent on old trees, but had no effect on San 

 Jose scale. The foliage was injured quite seriously Avhen a 5 per 

 cent solution was used. No damage was caused, however, from the 

 ai^plication of a 20 per cent solution on dormant trees, and at this 

 strength the insecticide proved effective in destroying the San Jose 

 scale. 



It is therefore quite apparent that the results of experiments 

 obtained from the use of kerosene and crude oil diluted and mixed 

 with other substances are nuich more at variance than those obtained 

 from the application of lime-sulphur wash. In fact, treatments with 

 these oils which have been reported by some entomologists .is per- 

 fectly harndess have been found exceedingly injurious when used by 

 other entomologists under apparently the same conditions. The con- 

 fusing and more or less contradictory results reported have led most 

 of the experiment stations to recommend that crude oils and kerosene 

 pure or in mixtures with water be applied with great precaution until 

 after considerable experience has been had in their use. 



FUMIGATION WITH HYDROCYANIC-ACID GAS. 



The great prevalence of San Jose scale has also led to extensive 

 experiments Avith fumigation by means of hydrocyanic-acid gas. 

 This remedy in numerous tests at almost all of the experiment sta- 

 tions which have been called upon to deal Avith the San Jose scale 

 has been uniformly effective in destroying this pest and practically 



a Virginia Sta. Bui. 152. 



