350 MASS. EXPERIMENT STATION BULLETIN 260 



of the relative efficiency of combined sprays of nicotine and copper 

 fungicides, for the control of thrips and blast or mildew, or both. 



Preliminary tests were made of a new spray material designed to serve 

 as an activator of nicotine, with the view of lowering the strength of the 

 nicotine sulfate spraj^ from present requirements without impairing its 

 efficiency against thrips. 



In cooperation with the Department of Botany, observations of onion 

 fields in the Yallej^ were made throughout the season to note the ap- 

 pearance and extent of blast and the correlation, if any, of this disorder 

 with insect activities. 



Control of the Plum Curculio in Apples. (W. D. Whitcomb, Waltham). 

 High temperatures in May and June stimulated the beetles to make two 

 to three times as many punctures per day as were observed in previous 

 years. Parasitism was exceedingly low. Early in the season the num- 

 ber of punctures made in sprayed and unsprayed fruit was approximately 

 equal, but two weeks later the beetles made 103 punctures in the un- 

 sprayed fruit and 12 in the sprayed fruit. Laboratory poison experiments 

 again indicated that lead arsenate at the rate of 2 pounds in 50 gallons 

 of water is the minimum dosage which should be used, and that calcium 

 arsenate is superior to lead arsenate in equal units by weight. Fish oil 

 sticker again increased the effectiveness of the poison but less than in 

 previous years. 



In confinement, beetles were attracted to and fed freely on dried frilit 

 baits containing various poisons. However, preliminary trials with these 

 baits in the orchard failed to show beneficial results, indicating that the 

 method of exposing the baits needs further study. 



Spray Residue Problem and Its Relation to Orchard Practides. (A. I. 

 Boiirne). Spraying and dusting experiments on the three standard varie- 

 ties of apples. Wealthy, Mcintosh, and Baldwin. Mere continued in 1929. 



The experience of the past summer has demonstrated the very great 

 influence which the type of season has upon the problem of spray residue 

 on fruit at harvest. Compared with the two previous years, the rainfall 

 in 1929 during the period between the calyx spray and harvest was rela- 

 tively insignificant, as noted below. 



Rainfall- — inches 



1927 1928 1929 



Wealthy 13.0 23.5 7.8 



Mcintosh 14.6 24.6 8.4 



Baldwin 18.5 25.0 10.3 



Under such conditions, miich of the spray deposit normally removed 

 from the fruit by rainfall persisted throughout the season. Consequently, 

 sprays could not be applied after early summer with any assurance of 

 safety, especially on Wealthy or Mcintosh. On the other hand, even the 

 late summer applications of sulfur — lead dusts on these same varieties were 

 made without encountering any difficulties as to residue. 



Biology and Control of the Carrot Rust Fly. (W. D. Whitcomb, Wal- 

 tham). The general infestation by the first generation of the carrot rust 

 fly was much less than in 1928 due to unfavorable conditions for 

 oviposition: consequently injury by the second generation was also some- 

 what lighter. 



