44 MASS. EXPERIMENT STATION BULLETIN 315 



secticide much more readily than can the chit which is partly or completely 

 enclosed by the older leaves. It would appear from the above figures that if the 

 varieties were of equal commercial value the resistant strains, such as the Sweet 

 Spanish types, would do much to solve the problem of thrips control. 



The disease attacking thrips, which was so prevalent in 1932 and to a lesser 

 degree in 1933, again appeared in considerable abundance throughout onion 

 fields in the Connecticut Valley. The relative scarcity of thrips and the severe 

 check to the seed onion crop caused by the prolonged drought did not allow it to 

 develop as rapidly as in the more favorable season of 1932. Attempts are being 

 made to produce cultures of the fungus, with the hope of introducing it artificially 

 in onion fields so that its presence would coincide more nearly with the peak of 

 thrips abundance. 



The Spray Residue Problem. (A. I. Bourne.) The limits of tolerance of both 

 lead and arsenic residue on sprayed fruit at harvest were still further reduced 

 for the shipping season of 1934, with the immediate prospect that within one or 

 two years the final limits of .014 grains per pound for lead and .01 grains per 

 pound for arsenic would be required. 



Through the cooperation of the State Office of the Food and Drug Administra- 

 tion, analyses were made for both lead and arsenic on samples of Mcintosh and 

 Baldwin, to determine the latest point in the present spray schedule when fruit 

 can be sprayed with reasonable assurance of safety and beyond which the danger 

 of residues over the tolerance is encountered. Samples of fruit as taken from the 

 orchard, samples which had been run through a commercial wiping machine, and 

 samples which had been subjected to washing in an acid bath were submitted for 

 analyses. The results of the analyses are as follows: 



McTNTOSH BALDWIN 



Last Spray Spray Residue — Grains per Pound Spray Residue — Grains per Pound 



Arsenic Lead Arsenic Lead 



Orchard-run Fruit 



1st Cover Trace .004 Trace .002 



2d Cover .006 .017 .002 .016 



3d Cover .008 .018 .008 .018 



4th Cover .... .008 .019 



Wiped Fruit 



1st Cover .002 .005 Trace .005 



2d Cover .004 .017 .003 .013 



3d Cover .006 .016 .004 .007 



4th Cover .... .... .008 .019 



Fruit Washed in Acid Bath 



1st Cover Trace .002 Trace .002 



2d Cover .002 .004 Trace .005 



3d Cover Trace Trace .002 .003 



4th Cover .... .... Trace .003 



The analyses indicated that in a summer such as 1934 Mcintosh could not be 

 sprayed later than mid-July without showing undue amounts of arsenic, and that 

 lead residue was excessive on fruit sprayed in mid-June. Because of the persis- 

 tence of the lead residue, Baldwins were in approximately the same position. 

 Wiping the fruit gave no appreciable relief in the case of either variety, although 

 the amount of visible residue on wiped fruit was noticeably less, and this treat- 

 ment resulted in a marked improvement in appearance and finish. Samples 



