36 MAINE AGRICUI.TURAI, e:xPE;RIME;nT STATION. I9II. 



Changes in the chemical nature of bordeaux are produced by 

 weather conditions and by atmospheric moisture in particular. 



The injurious action of bordeaux is ascribed to the solvent 

 action of the cell sap and of meteoric waters following spray- 

 ing, upon the copper hydroxide of the mixture. The copper- 

 thus left in solution is the toxic agent. 



No great importance is attached by Hedrick to the nature of 

 the lime (air slaked or freshly slaked), used in making the 

 mixture as a factor in producing injury. 



Crandall, after a series of carefully controlled experiments 

 covering a number of seasons, arrived at the following conclu- 

 sions : 



Air slaked lime in bordeaux gives more injurious results than 

 when freshly slaked lime is used. 



Equal and full dilution of the two ingredients gives least 

 injury. 



Excess of lime is advantageous only as a subsequent spray 

 and not as an addition to the bordeaux. 



Properly prepared bordeaux gives injury under unfavorable 

 weather conditions ; rain and dew are important assisting factors. 



Small amounts of copper become soluble soon after the ap- 

 plication of bordeaux, and this solvent action increases more 

 rapidly with meteoric waters than with water artificially applied. 



The physical condition of the leaves bears a relation to the 

 amount of injury. Lesions produced by insects and fungi ren- 

 der foliage more susceptible to injury. 



Recurrent leaf yellowing epidemics have no direct relation to 

 weather conditions, and evidence of bordeaux as the sole cause 

 of yellowing is not established. Copper sulphate solutions, 

 however, when injected directly into trees produce yellowing, 

 the degree of injury depending on the strength of the solution. 



Groth's work was confined to the peach after some prelimi- 

 nary work which included the apple and the plum. His experi- 

 ments, conducted both in the field and under control conditions 

 under glass, led him to a theory of spray injury involving, among 

 the chemical and meteorological factors previously recognized, 

 a physiological one. He finds : 



Bordeaux injury is independent of the density of the appli- 

 cation. 



Copper is the toxic agent. 



