Arizona Agricultural Experiment Station 609 



formed, the surface soon cracks enough to permit drying of 

 the mesocarp beneath. Some of the hyphae in contact with 

 the tannin layer finally succeed in penetrating the tannin 

 cells in which they may actually be found embedded. Other 

 hyphae pass through natural breaks in the tannin layer and 

 the mycelium eventually reaches the endocarp. 



SUSCEPTIBILITY OF VARIOUS DATES TO DATE ROT 



No variety of date appears to be entirely immune to the 

 attack of date rot fungi so far as our Arizona orchards are con- 

 cerned. The Deglet Noor, the most valuable of the varieties 

 in cultivation here, is probably the most susceptible. 



CONTROL 



Owing to the torching of the date palms in the Yuma and 

 Tempe orchards for the eradication of scale, control measures 

 for date rot could not be undertaken during the season of 1920. 

 Fruit clusters sprayed this season with 4-4-40 Bordeaux mix- 

 ture have remained free from date rot fungi thus far. 



COTTON BLACK ARM AND ANGULAR LEAF-SPOT 



Black arm and angular leaf-spot were present in nearly 

 every field of Pima-Egyptian cotton in the State last season. 

 Injury to the crop included the usual stem lesions, destruction 

 of leaf tissue and leaves, boll spotting, premature ripening, and 

 fiber staining. Some fields were reported to be practically 

 ruined. The appearance of the disease in fields newly cleared 

 of mesquite added to the evidence that the casual organism, 

 Bacterium malvacearum, i's carried by the seed. Unfortunately, 

 cotton growers are slow to adopt the method of seed treatment 

 with sulphuric acid which, in the South, has proved to be an 

 efficient control. 



Considerable areas of alkali land lie within the cotton 

 districts of Arizona and alkali is brought into fields in irriga- 

 tion water. The question has arisen as to whether alkali in- 

 fluences the susceptibility of cotton to the black arm organism. 

 Under a cotton project, this Department is attempting to answer 

 the question. Duplicate plots of Pima-Egyptian cotton have 

 been planted at Sahuarita on alkali-free soil and at Yuma on 

 alkali soil, with untreated seed, seed treated with concentrated 

 sulphuric acid, seed treated with sulphuric acid and then with 



