172 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Restricted irrigation of young cotton. — The production of cotton 

 in Arizona and California is entirely dependent upon irrigation. 

 The proper application of water largely determines not only the 

 yield but also the quality of the lint, so that a knowledge of the 

 w^ater requirements is essential to scientific farming. Though no 

 regular quantity or interval for applying water can be prescribed, 

 on account of wide differences of soil and other conditions, the irriga- 

 tion treatment can be adjusted to the needs of the crop by observing 

 the behavior of the plants, as experiments have shown. 



In general, cotton should be irrigated so as to keep the plants grow- 

 ing steadily and to avoid either forcing or checking their develop- 

 ment. While the plants are small and not yet flowering care should 

 be taken to apply water only as needed, since too much water may 

 force rank growth, especially with rich soil and warm weather. It 

 is important to establish the young plants in a normal habit of 

 growth before the flowering stage is reached. After a normal fruit- 

 ing condition is attained, the plants are not so easily forced into 

 rank growth by the application of water, even in excess of the actual 

 requirements, so that the summer irrigation problems are simplified. 



Irrigation of cotton in the fruiting period. — After flowering begins 

 water should l)e applied more frequently, enough to keep the plants 

 growing and the flowers well down from the top. If the plants 

 bloom at the top it is apparent that irrigation has been delayed too 

 long and growth restricted. The general wilting of the plants is a 

 sign of water exhaustion, which may cause boll shedding and injure 

 fiber quality, but slight wilting in the afternoon of a hot day is not 

 abnormal. A method that has been successful with Pima cotton in 

 the^Salt River Valley is to irrigate the general field wdien the plants 

 in the drier spots begin to wilt in the morning. With these features 

 to guide in applying water, a steady growth should be maintained 

 until the latter part of August. Less water is required in Septem- 

 ber and October, but to mature the bolls properly the plants should 

 not be allowed to wilt. A need of irrigation in the late season is 

 sometimes shown by a decided yellowing of the plants, even though 

 no wilting occurs. 



Cultural control of the holl loeevil. — An important step has been 

 taken toward avoiding weevil injury in extending the use of the new 

 method of close spacing the plants in the rows. This has been 

 described in several publications as the "single-stalk system," calling 

 attention to the advantages of restricting the size of the plants and 

 controlling their habits of branching. The improved method pro- 

 duces upright plants with only a single primary stalk and avoids 

 the formation of the spreading secondary stalks, side stalks, or 

 vegetative branches which arise from the base of the primary stalks 

 and are entirely different from the fruiting branches that bear the 

 flowers and bolls. The objection to the secondarie's, or side stalks, 

 is that they stand out obliquely and close the lanes between the 

 cotton rows, especially if the cotton grows too rank, as it tends to 

 do where boll weevils are abundant. Large plants with spreading 

 side stalks are especially undesirable under weevil conditions, be- 

 cause the crop is later to set and later to mature on large plants. 



Recognition of two kinds of cotton ?>ra?icAes_.— -Though the single- 

 stalk system of cotton planting is very simple it is not easily under- 



