ORCHARD SPRAYING EXPERIMENTS. 35 



face may be greatly roughened, corrugated, or show pustule or 

 teat-like formations. In very severe cases the skin may crack 

 and exhibit V-shaped clefts in the flesh of the fruit (Fig. 50). 



Bordeaux Injury; Literature and Comment. 



The toxic action of copper compounds on plants has been 

 a fertile field of investigation for botanists and plant patholo- 

 gists at home and abroad, but the most recent important con- 

 tributions to the literature of bordeaux injury are those of 

 Prof. U. P. Hedrick, New York,* Prof. C. S. Crandall, Illi- 

 nois,** and Dr. B. H. A. Groth, New Jersey.*** 



Hedrick's extended investigations and experiments developed 

 the following points : 



Spray injury is prevalent in all sections of the world where 

 bordeaux mixture is used. 



Excess of lime is not a preventitive, nor improperly made 

 bordeaux the sole cause of injury. 



Injury increases proportionally with the amount of copper 

 sulphate used. 



Wet weather following applications is a favorable condition 

 for the production of injury. 



Yellowing and leaf fall are dependent upon the amount of 

 injury. 



Different species vary in susceptibility to injury; the peach, 

 apricot and Japanese plum being most readily affected, the com- 

 mon plum, quince and apple showing more resistance. 



Varieties within the above groups vary in susceptibility to 

 injury.f 



Somewhat similar injuries occur on trees not sprayed with 

 bordeaux, and are ascribed to factors of frost, fungi, arsenicals 

 and the lens or "burning glass" action of drops of water on the 

 fruit in intense sunlight. 



* Hedrick, U. P. "Bordeaux Injury". New York Agric. Expt. Sta. 

 (Geneva), Bulletin 287 (1907). 



** Crandall, C. S. "Bordeaux Mixture". Illinois Agric. Expt. Sta. 

 Bulletin 135 (igog). 



*** Groth, B. H. A. "Contribution to the Study of Bordeaux Injury 

 on Peaches." New Jersey Agric. Expt. Sta. Bulletin 232 (1910). 



t Note. — Attention is called to Hedrick's classification of apple va- 

 rieties in relation to their susceptibility to spray injury which is given 

 on pp. 346-349, of Bulletin 185 of the Maine Station. 



