OZOXIUM BOOT EOT 



17 



OBSERVATIONS DURING THE SUMMER OF 1924 



Prior to June 30 a few root-rot centers were present in border 

 C 2-24 at the United States Field Station, Sacaton. Ariz. This 

 border, planted to Pima cotton, was included in a spacing experi- 

 ment. The first three rows consisted of plants widely spaced (12 

 to 15 inches), whereas the other four rows were closely planted 

 (about 12 to 15 plants per foot). 



By taking a count of the number and location of the dead plants 

 on alternate days an opportunity of watching the spread of root 

 rot under two different conditions in one plat was afforded. During 

 the growing season the border was irrigated on April 15, May 23, 

 June 24, July 18. August 12. September 2, and September 26. From 



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Fig. 2. — Diagram showing the number of cotton plants killed by root rot in 

 border C-2-24 at Sacaton. Ariz., each alternate day from July 1 to October 

 1, 1924 



June 30 to October 1. 0.99 inch of rain fell in the form of scattered 

 showers. The heaviest shower consisted of 0.33 inch. The rainfall 

 for the summer months being below normal and almost negligible as 

 far as the quantity is concerned, it is assumed that irrigation alone 

 influenced the progress of root rot. 



Figure 2 shows the death rate of the plants in the border. If 

 this diagram is studied it will be found that, beginning with the 

 second week in July, the mortality of the plants was extremely high 

 and remained so with the exception of two pronounced fluctuations 

 until the second week in August, when the death rate dropped very 

 rapidly and continued to do so more or less until the end of the 

 season. In other words, almost 75 per cent of the plants which 

 died in this border did so during the interval between July 8 and 

 August 15. 



