10 BULLETIN 1153, U. S. DEPARTMENT OF AGRICULTURE. 



in addition to weevil protection, is that farmers of the drier dis- 

 tricts are less troubled with weeds, so that costs of cultivation are 

 lower than in humid regions. 2 



The spacing problem is complicated by the very wide range of 

 seasonal conditions, the Texas climate being notoriously capricious. 

 That any one method of spacing will assure the largest possible 

 results under all conditions is too much to expect, but the method 

 that is safest, in the sense of giving the best average of results under 

 varied conditions and for a period of years, would be reckoned as 

 the most practical. To develop such a method and to secure the 

 evidence that would be necessary to establish it in popular recogni- 

 tion as the best must require many experiments and a wide range of 

 practical experience as well as a great amount of interest and infor- 

 mation in the hands of the farmers. Since it is not to be expected 

 that farmers will make a practical and effective use of a cultural 

 method that they do not understand, careful study and observation 

 of the facts are a necessary preliminary to the practical use of better 

 methods of spacing. 



With differences of seasons, soils, and other variable factors to be 

 taken into account, the weevils may be very irregularly distributed, 

 and cultural experiments may miscarry or the results may be de- 

 ceptive if the behavior of the weevils is not considered. One side or 

 one corner of a field may be thoroughly infested before any damage 

 is done in other parts of the same field. The factor of weevil infes- 

 tation may interfere seriously with the testing of varieties or with 

 cultural experiments by methods that for other purposes are consid- 

 ered most reliable. 



Repeated side-by-side comparisons of two varieties or two cultural 

 methods, as represented by small blocks or strips of cotton planted 

 in alternation, give the most direct and convincing evidence when 

 consistent results are secured. From 4 to 6 rows of the same kind of 

 cotton or representing the same treatment are planted in each block, 

 the blocks are repeated 3 or 4 times in alternation, and the cotton 

 from each row is picked, weighed, and recorded separately. The 

 last precaution, of records of individual rows, is important as afford- 

 ing the best evidence to show how uniform or how irregular the con- 

 ditions of the experiment actually were and whether any differences 

 were consistently shown in the repeated comparisons. 



But such methods of testing may not give significant results if the 

 weevils are very abundant. Differences that might be very im- 

 portant in separate fields of cotton may not be shown definitely in 

 side-by-side plantings, or mav even appear reversed if weevils are 

 bred in larger numbers on an adjacent early variety, early planting, 

 or early thinning, so that the cotton of later development suffers 

 worse. Thus, the true advantage of closer spacing of plants in the 

 rows may not be shown in some experiments if the weevil population 

 is too large at the beginning of the experiment and is being increased 

 rapidly by breeding more weevils in earlier flower buds of adjacent 

 wide-spaced rows. In such cases there may be more weevils to attack 

 the buds of the close-spaced rows than in a field planting not ad- 

 jacent to other cotton or if whole communities planted their cotton 



* Coad, B. R.j and Cassidv, T. P. Cotton boll weevil control by the use of poison. 

 n. S. Ocpt. Agr. Bui. 875, 31 p. 1920. 



