EXPERIMENT STATION WORK WITH INSECTICIDES. 253 



be sprayed on infested trees as soon as possible after October 15. It is 

 not considered necessary to wait until the leaves have all fallen. It is 

 apparently safe to apply the insecticide as soon as the young shoots 

 are mature in the fall. In cases of had infestation it is reconiniended 

 that the application be rejjeated about two weeks later. 



The New York State Experiment Station" has thoroughly tested 

 the use of oils as a spray for the destruction of scale insects. In one 

 series of winter experiments it was found that kerosene with a fire 

 test of 150° killed peach trees when one application was made of a 

 20 per cent mechanical mixture with water, and seriously injured 

 plum trees Avhen applied in a 40 per cent mixture. At the same time 

 pear and apple trees were not injured except when treated with pure 

 kerosene and even then the harm was slight. In the early experiments 

 at this station a 20 per cent mechanical mixture of kerosene had no 

 effect upon the scales. Summer applications of refined kerosene were 

 found to be dangerous, since the leaves were badly burned whenever 

 the kerosene was used at a percentage high enough to kill the scale 

 insects. Subsequently the station carried out experiments with crude 

 petroleum as a Avinter insecticide. In these tests it was found that 

 ennilsions containing 25 per cent or more of crude petroleum seriously 

 injured or killed peach trees, while plum and apple trees were not 

 injured except when a 40 per cent or higher emulsion was used. 

 During the same tests cherry and pear trees were not injured even by 

 undiluted petroleum. Spring applications caused serious injury to 

 plum trees when the petroleum was used undiluted, slight injury 

 when used in a 60 per cent solution, while the application was harm- 

 less when a 40 per cent solution was used. Comparative tests under- 

 taken to determine the percentage of petroleum required to kill 

 hibernating San Jose scales showed that the insects are not killed by 

 a 25 per cent mixture, while 40 per cent and higher percentages 

 destroy the scales, whether aj)plied in winter or spring. It was found 

 unsafe, however, to use a 40 per cent emulsion after the buds had 

 swollen. In general, the station concludes that vigorous trees are less 

 lial)le to be injured by crude petroleum than sickly ones. Peach and 

 plum trees appear to be more sensitive than ai:)ple and cherry trees. 

 Moreover, there seems to be less danger of injury if trees are sprayed 

 in curly spring rather than during the fall or winter. 



The final results of experiments with oils at the New^ York State 

 Station indicate that spraying with kerosene or crude petroleinn is 

 safe and effective when done under the proper conditions. If kero- 

 sene is to be used oidy the best grades should be purchased, since 

 lower grades are more or less dangerous. Mechanical mixtures rang- 

 ing from 15 to 20 per cent of oil may be applied to apple and pear 



oNew York State Sta. Buls. 11)4, 201i, 213. 



