A BACTERIAL DISEASE OF THE PEACH* 



James B. Rorer 



From time to time during the past five or six years peach 

 growers in various sections of the country have called attention 

 to a shot-hole disease of peach leaves which, in wet seasons 

 at least, has caused a great deal of premature defoliation. In 

 1903 Mr. P. J. O'Gara, of the Bureau of Plant Industry, found 

 it prevalent in Georgia and suggested that it was of bacterial 

 origin. During the same season Clinton* observed a leaf-spot 

 disease, evidently the same, in Connecticut, and noted it in his 

 report for that year.f 



It was again found in Georgia in 1905 by Mr. W. M. Scott, 

 of the Department of Agriculture. In 1906, 1907, and also 

 in the past season the writer, who undertook a somewhat de- 

 tailed study of the disease found it to be prevalent throughout 

 the South and Middle West, and, in those sections at least, it is 

 the commonest shot-hole disease of peach leaves, the Cercospora 

 leaf-spot being but rarely met with. That a bacterium caused the 

 disease was proved by inoculation experiments. A bacterial 

 disease of peach twigs and of the fruit was also found, and it 

 seems probable that they, as well as the leaf-spot, are caused 

 by the organism in question. 



The form occurring on the leaves is by far the commonest 

 and most wide spread. It causes somewhat angular, purplish- 

 brown spots )/% to Y\ inch in diameter which, when infections 

 have been numerous, coalesce so that quite large areas of the 

 leaf may be involved. .The diseased tissues soon fall out, giving 

 a shot-hole effect. Leaves which are at all badly affected soon 

 drop to the ground, so that the trees may become prematurely 

 defoliated. This is especially true in orchards which have not 

 been well pruned and cultivated. 



In August, 1906, very small spots from fresh leaves were 



* Paper read at the meeting of Section G, A. A. A. S., Baltimore, 1908. 

 f Rep. Conn. Agric. Exp. Sta. 26: 337. 1903. 



23 



