32 MASS. EXPERIMENT STATION BULLETIN 305 



serious burning of foliage. Similar tests in commercial orchards in manj' cases 

 resulted in even more serious damage than that in the college orchards. Burn 

 was first noted following the extremely hot weather in late June, and in many 

 subsequent instances was associated with similar periods of high temperature, 

 particularly when accompanied with a high relative humidity. Lead arsenate 

 in parallel tests and under the same conditions caused slight foliage burn but in no 

 case was the injury comparable to that following calcium, manganese, or zinc 

 arsenate. 



Weather conditions during late summer and early fall, particularly during the 

 period from the last spray or dust application until the harvesting of the fruit, 

 w"ere favorable from the standpoint of the residue problem. The total rainfall 

 during August was nearly two inches over the normal and the outstanding feature 

 of the weather during September was the unusually large rainfall of over twelve 

 inches, a great part of which occurred just before the harvesting of Mcintosh. 

 From the residue standpoint the danger to the main varieties, Mcintosh and 

 Baldwin, was practically eliminated, and growers who dusted in the late season 

 applications experienced no difficulty. 



In cooperation with the State office of the Food and Drug Administration, 

 samples of Mcintosh and Baldwin were collected and forwarded for analyses for 

 both lead and arsenic to determine how far the present spray schedule could 

 be safely followed and what changes would be necessary. The results of these 

 analyses have not been received. The excessive rainfall during August and 

 September would so reduce the amount of residue at harvest that it is doubtful 

 whether these figures would be applicable to a season of more normal precipitation. 



Under present conditions, if a grower hopes to avoid the danger of lead or 

 arsenical residue without the necessity of washing his fruit, it is recommended 

 that lead arsenate in an amount exceeding 3 pounds to 100 gallons should not be 

 applied within 8 weeks of harvest and that no arsenical spray be applied within 

 6 weeks of harvest. Growers who depend upon dusting, however, may safely 

 employ at least a 90-10 sulfur-lead arsenate dust as late as 4 weeks before 

 harvest. 



Systematic Study of Oil Sprays. (A. I. Bourne in cooperation with the Depart- 

 ment of Chemistry.) Three samples of miscible oil, prepared under identical 

 conditions and with the same emulsifying agents, were used in the tests this 

 season. The basic oils were paraffin base lubricating oils of approximately the 

 same viscosity. The specific gravity of the samples was respectively 0.86, 0.89 

 and 0.91, and the samples varied from 75 to 86 per cent in their degree of unsul- 

 phonated residue. These were applied in a block of plums while the trees were 

 in delayed dormant stage of bud development, to test their effectiveness against 

 overwintering eggs of European red mite. They were used at 2 and 3 per cent 

 strengths of the basic oils. 



When mixed with water in preparation for the spray, the samples of higher 

 specific gravity went into solution very readily. The sample of 0.86 specific 

 gravity was emulsified with considerable difficult^' and required constant and 

 vigorous agitation. None of the samples when once in solution showed any 

 evidence of breakdown or separation of free oil. There was no indication of 

 burn or retarding of bud development following the application of any of these 

 oils, at either dilution. 



All of the samples gave 98 to 99 per cent control of European red mite. There 

 was no significant difference in effectiveness in any case; but the light infestation 

 of red mite in the college orchards made any fine distinctions in effectiveness 

 impossible. 



