6 



CIRCULAR 7 4 7, U. S. DEPARTMENT OF AGRICULTURE 



SMOOTH BROMEGRASS 



Bacterial Blight (Chocolate Spot) 



Bacterial blight, caused by Pseudomonas 

 coronafaciens (Elliot) Stapp var. atropurpurea 

 (Redely and Godkin) Stapp, attacks several 

 grasses and is a serious disease of smooth brome- 

 grass (Bromus inermis (Leyss.)). Initial symp- 

 toms appear as circular to elliptical water- 

 soaked areas of uniform size on the leaf blades. 

 These soon turn purplish black, and it is from 

 this stage that the common name chocolate spot 

 originates. This is a misnomer, however, as 

 lesions more frequently coalesce to form typically 

 blighted areas involving the entire blade and 

 sheath (fig. 5). As blighted leaves wither and 

 die, the lesions fade to a rusty brown, and occa- 

 sionally a dry exudate is present. Bacterial 

 blight often attains epiphytotic proportions by 

 mid- June. Its development is favored by 

 periods of humid, hot weather. The causal 

 organism is readily cultured and produces a 

 green-fluorescent, pigmented type of colony on 

 artificial media. 



Figure 5. — Bacterial 

 blight on smooth 

 bromegrass. 



