Arizona Agricultural Experiment Station 61] 



Growers almost invariably attributed their losses to frost in- 

 jury, but laboratory studies revealed the presence of two bac- 

 teria which were capable of completely rotting healthy heads 

 of. lettuce. Inoculated heads were usually reduced to a black 

 liquid within two or three weeks. Studies are in progress to 

 determine the identity of the bacteria and the source of infec- 

 tion. Bacterial rot of lettuce has been reported from eastern 

 states and the infection there has been attributed to poorly 

 rotted manure used in fertilizing lettuce fields. In Arizona the 

 fields attacked consist of silt, and no manure of any kind has 

 ever been used. 



Among other diseases determined in infected plants sent 

 in by county agents, farmers and others, or collected by the 

 Department, are the following : 



FIELD CROPS 



Alfalfa. 



Leaf spot caused by Pseudopeziza medicaginis, from Salt 

 River and Yuma valleys. 



White spot, physiological, from Yuma and Salt River 

 valleys. 



Bacterial blight caused by Bacterium medicaginis, from 

 Salt River and Rillito valleys. 



Girdle, cause unknown, from Yuma, Casa Grande and 

 Mesa. 



Rust caused by Uromyces stiixitus, from Yuma, Casa 

 Grande, and Mesa. 



Barley. 



Leaf-spot caused by Helminthosporium sativum, from 

 Agua Caliente. 



Covered smut caused by Ustilago hordei, from Mesa. 



Cotton. 



Sore shin caused by Rhizoctonia sp., from Salt River 

 and Santa Cruz valleys. 



Wilt caused by Fv^arium vasinfectum, from St. David. 



Black arm and angular leaf spot caused by Bacterium 

 mulvacearum, from Salt River and Santa Cruz valleys. 



Root rot caused by Ozonium omnivorum, from Salt River 

 and Santa Cruz valleys. 



Watermelon, Cantaloupe. 



Anthracnose caused by Colletotrichum lagenarum, from 

 St. David and Jerome Junction. 



