ANNUAL REPORT, 1936 51 



The appearance of blast terminated the studies in early August. The Sweet 

 Spanish types eventually succumbed although persisting later than Danvers. 

 The increased infestation of the Valencia Sweet Spanish was undoubtedly due 

 to migration from blasted plants of adjoining varieties. 



There was very little evidence of the fungous disease of thrips. The preva- 

 lence of blast throughout the Connecticut Valley during the last two seasons, 

 which killed the plants before the normal time of appearance of the disease, 

 has apparently reduced this to a position of little importance. 



The Spray Residue Problem. (A. I. Bourne.) No further reduction in 

 limits of tolerance on lead residue was made, so that for the shipping season of 

 1936 the figure remained at .018 grains per pound of fruit for lead and .01 

 grains per pound for arsenic. This action was to a great extent in recognition 

 of the exceeding persistence of lead deposits on fruit and the difficulty of re- 

 moval, as well as the complication of the problem presented by the unusually 

 dry weather conditions prevailing between the spraying season and harvest. 

 Analysis of Mcintosh fruit which had received the regular sprays up to and in- 

 cluding the 3d cover on July 13 showed .019 grains of lead and .012 grains^of 

 arsenic per pound of fruit. Such a residue exceeds the present established limits 

 of tolerance for both materials. Fruit receiving the complete schedule of four 

 cover sprays showed .026 grains of lead and .013 grains of arsenic per pound, 

 indicating that even with the dosage of lead arsenate reduced from 3 pounds to 

 2 pounds per 100 gallons in the late July spray, the amount of residue built up 

 rapidly. Since the 3d and 4th cover sprays are designed primarily for control 

 of apple maggot, the above figures strengthen the recommendation for the use 

 of dusts for those applications, since dusts have proved effective against apple 

 maggot, and analyses have shown no objectionable residue on fruit dusted as 

 late as three weeks before harvest. 



In studies of possible substitutes for lead arsenate, Calrite, a product of the 

 Niagara Sprayer and Chemical Company, for the third successive season caused 

 no trace of foliage injury or russeting of fruit on either Mcintosh or Baldwin. 

 When supported by the colloidal spreader Fluxit, Calrite also proved substan- 

 tially equal to lead arsenate in control of plum curculio and codling moth, 

 as shown in the following table. 



Percentage of Percentage of fruit showing injury from — 



clean fruit 



Material Curculio Codling Moth Scab 



Bald- Bald- Bald- B.ald- 



Mclntosh win Mcintosh win Mcintosh win Mcintosh win 



Calrite and Fluxit 94.9 85.3 0.2 0.0 0.9 3.2 1.7 1.2 



Lead arsenate 92.5 92.9 0.0 0.2 0.4 2.6 6.1 0.2 



Both materials were used with the same fungicides: lime-sulfur in pre- 

 blossom applications, and wettable sulfur in the calyx and four cover sprays. 

 It will be noted that in such a program the calcium arsenate also compared 

 very favorably with lead arsenate in control of scab. Two experimental samples 

 of calcium arsenate, furnished by the Crop Protection Institute and applied in 

 late cover sprays on a block of young non-bearing trees, gave no trace of foliage 

 injury or premature drop of leaves, and both products appeared to be worthy 

 of further tests on a commercial scale. 



In a cooperative experiment with the Crop Protection Institute one block of 

 the orchard was devoted to a comparison of an experimentally prepared basic 

 zinc arsenate with standard lead arsenate. One section of the orchard received 



