BULLETIN No. 207. 



DEPARTMENT OF ENTOMOLOGY. 



INJURY TO 1 GLIACJE 15Y ARSENICAL SPRAYS. 



I. THE LEAD ARSENATES. 



BY H. T. FEKN'ALD AND A. I. BOURNE. 



It lias long been knowai that arsenical poisons sprayed upon foliage will 

 at times produce injury, or a "burning" of the leaves. For this, four 

 explanations have been offered, viz., (1) that the arsenic (either AsaO:; 

 or As..)0:„ as the case might be) was present in the material, uncombined 

 with any base; (2) that it M-as so loosely combined with the base as to be- 

 come liberated from it during the addition of water in preparing it for 

 application to the foliage; (3) that this liberation took place more or less 

 gradually on the leaves after the spray had been applied, as a result of 

 influences acting upon the material through the air; and (4) that injury 

 was due to the presence of injurious impurities in the material. 



Fault}^ methods of manufacture might easily result in producing a sub- 

 stance containing some arsenic, either free or so poorly combined that upon 

 the addition of water the combination W(juld break up, at least to some 

 extent. The use of poor materials from which to make the lead arsenate 

 might very possibly result in the presence of injurious substances. The 

 liberation of arsenic upon the tree by atmospheric influences, however, 

 comes distinctly in a different class; and the statement sometimes made, 

 that spraying a tree with water under the right conditions may result in 

 burning, if true, also suggests that atmospheric conditions must not be 

 overlooked. The entire problem, therefore, of ascertaining what factors 

 are reallj^ responsible for foliage injury following arsenical spraying has 

 been iuA'estigated during a ];)eriod of about ten years. 



This bulletin reports the results of this work with the various lead ar- 

 senates. Similar reports upon arsenates of linae and Paris green are 

 nearly ready for publication, together ^vith notes on a number of other 

 arsenicals which have been tested more or less. 



The planning of the project, the plotting and analysis of the results, and 

 the preparation of the material for publication are the work of the senior 



