18 



MASS. EXPERIMENT STATION BULLETIN 207. 



In order to obtain some idea of the relative resistance of the apple, 

 cherry, plum and peach to arsenical sprays. Fig. 23 has been prepared, the 

 material used in each case being the pure acid lead arsenate paste applied 

 in clear weather. The elm and pear are not included, for as already stated, 

 no injury points were obtained. If their safety lines come into the chart 

 at all, they would only cross the upper right square, and probably would 

 not occur unless close to H90 T95. 



Humiditu, 



S-i' 





6b- 



Fig. 23. — Safety lines for spraying with pure acid lead arsenate in 

 clear weather: 1, apple; 2, cherry; 3, plum; 4, peach. 



General Conclusions, 



An analysis of the effects of temperature, humidity and light given in 

 detail above brings out several features of interest: — 



1. The neutral lead arsenate used, even though it was not entirely pure, 

 proved the safest of the materials in clear weather, and in most cases was 

 better even in cloudy weather than the others. 



2. The clear weather spraying is safer than the cloudy weather, though 

 the difference generally is not great. 



3. The indication is that sprajang at high temperatures can be done 

 safely if the humidity is low. 



4. Spraying can be carried out safely at high humidities if the tem- 

 perature is low, though the humidity cannot run up as high as the tem- 

 perature can at the other end of the line. Thus spraying the apple seems 

 to be safe at TOO when H is not over 69, but is not safe at H90 when T is 

 above 67. 



5. Between the ends of the safety lines of the charts, i.e., with medium 

 T and H, both seem to have an influence. 



6. With the apple and cherry the safety lines are straight, while in the 

 plum and peach most of them " elbow," indicating that the T and H fac- 



