98 MASS. EXPERIMENT STATION BULLETIN 210. 



used for the other tests, and in every case injury followed, generally 

 severe. Clear or cloudy weather seemed to give little difference in the 

 results, and spraying at low T and H combinations produced injury as 

 certainly as with high combinations of these factors. Extensive tests 

 of zinc arsenite, therefore, were not continued. 



SUMMARY. 



1. Pure acid calcium arsenate is not on the market. Tests with it in- 

 dicate in a general way that the same factors determining injury to foliage 

 hold good as with the lead arsenates, but that the safety lines run lower. 



2. With commercial calcium arsenate the safety lines run about as high 

 (in some cases a Httle higher) as with the pure material, but lower than 

 with the lead arsenates. In the case of the peach, however, the safety 

 line does not differ greatly from that obtained with the lead arsenate 

 powder. 



3. It is possible that the excess of lime in the commercial calcium 

 arsenate may be sufficient to prevent the arsenic pentoxide from enter- 

 ing into solution. Further tests are needed on this point, as considerable 

 time and bother can be saved if the addition of milk of lime is unnecessary. 



4. In general, lime arsenate does not give as satisfactory results as the 

 lead arsenates, the range of T and H combinations at which it is safe 

 being more limited. 



5. The spraying of different kinds of trees with commercial calcium 

 arsenate cannot always be done with safety on the same day. The treat- 

 ment may be safe on some kinds of trees under conditions which make it 

 dangerous to others. 



6. Calcium metarsenite is not safe for use on fruit tree foliage. 



7. The same is true for magnesium arsenate and zinc arsenite — at 

 least for the samples tested. 



