44 MASS. EXPERIMENT STATION BULLETIN 327 



The fungous disease found to be attacking thrips in previous seasons was 

 present but not at all abundant. The relative scarcity of thrips and the pre- 

 mature death of the plants early in August due to blast gave little opportunity 

 for its development. 



The Spray Residue Problem. (A. I. Bourne.) The limit of tolerance on 

 lead was again reduced for the shipping season of 1935. With the assurance 

 that annual reductions will be made until the recognized minimum tolerance of 

 .014 grains per pound for lead residue is reached, the problem is annually be- 

 coming more acute. 



Readjustments were made in the spray schedule recommended for Massa- 

 chusetts orchards. Emphasis was laid on lessening the dosage of lead arsenate 

 in the late summer sprays, particularly on early and mid-season varieties. 

 Growers were urged to substitute a dust schedule for the late cover sprays where 

 possible. Curtailment of funds prevented the cooperation by the State office 

 of the Federal Food and Drug Administration in the analysis of fruit for lead 

 and arsenic residue. Necessary readjustments due to transfer of this work to 

 the station chemists have delayed the work of analysis so that the figures are 

 not yet available. 



Experiments with possible substitutes for the standard lead arsenate were 

 centered chiefly upon a calcium arsenate and a specially prepared lead arsenate. 

 Calcium arsenate automatically eliminates the lead residue problem which 

 offers the major difficulty. Practically all brands of calcium arsenate, however, 

 have been found to seriously injure apple foliage and are apt to russet fruit. 

 The particular brand used in our tests, a product of the Niagara Sprayer and 

 Chemical Company under the trade name Calrite, has for two successive seasons 

 been used in a complete schedule on Mcintosh and Baldwin without causing 

 either foliage injury or russeting of fruit. In the tests of 1934 this did not prove 

 as effective against curculio and codling moth as did lead arsenate. In 1935 

 this material was given increased adhesiveness by the addition of a colloidal 

 spreader and proved much more effective, as shown in the following table. 



Percentage of Fruit Showing Injury from — 

 Material 



Calrite and Fluxit 



Lead arsenate 



Both arsenicals were used in combination with the same fungicide. The 

 amount of injury from scab was undoubtedly due to the materials used to 

 increase the adhesiveness of the calcium arsenate. It is significant, however, 

 that both the major insect pests were satisfactorily controlled. 



A specially prepared type of lead arsenate which is being developed by the 

 Crop Protection Institute was compared with standard lead arsenate. One 

 of the college blocks was divided so that one-half was sprayed with each material 

 and results were checked at harvest on three varieties: Ben Davis, a variety 

 which russets easily; Rhode Island Greening; and Mcintosh. The results are 

 as follows: 



