86 NEW YORK STATE MUSEUM 



temperature in the spring checks the flow of sap and, following an 

 application of oil, is very liable to result in greatly increased pene- 

 tration by the insecticide, sometimes with disastrous results. It 

 is very likely that the apparent immunity of different varieties 

 depends in considerable measure upon seasonal variations in the 

 pressure of the sap, due to an early or late ripening of the wood 

 and possibly to differences in the penetrability of the bark. 



Record of injury following applications of a miscible oil. The 

 following records are not intended to be exhaustive and are made 

 public simply to establish the fact that serious injury may follow 

 the use of oil preparations upon dormant trees. 



In June 191 1 our attention was called to the serious condition 

 of many hard maples in Mount Vernon, sprayed the preceding 

 spring with a miscible oil. Some of the trees most infested by in- 

 sects, it is stated, were sprayed March 24th and again May 20th. 

 There were some 2136 hard and soft maples which received this 

 application. The soft maples were practically unharmed, while 

 many of the hard maples, in fact all marked as having been sprayed, 

 which we examined June 20th, showed evidence of recent ser- 

 ious injury, many being practically dead. This was true of small 

 trees three inches in diameter, as well as of maples some eight 

 inches in diameter, all, with very few exceptions, appearing 

 as though they had been in full vigor the preceding sea- 

 son. Trees on one side of the street or on one block were affected, 

 while unsprayed trees of the same variety on the opposite side of 

 the street or on adjacent blocks were in normal condition. In 

 some instances the damage was limited to limbs most easily reached 

 by the usual type of spraying outfit. We were unable to find suffi- 

 cient evidence of injury by insect pests or damage following gen- 

 eral adverse conditions to account for the sudden death of so many 

 trees in a closely restricted area. Additional details of our findings 

 at that time are given in the report for last year (27th report of 

 the State Entomologist, New York State Museum Bulletin 155, 

 pages 88-92). 



Personal observations during July and August of last season 

 (1912) showed that practically all the trees noted as being badly 

 injured the preceding year, had been removed and replaced by 

 small trees. We were informed that 449 maples had been reset. 

 Furthermore, some of the trees less seriously injured in 191 1 

 showed dead limbs or patches of dead bark, and the prospect is 



