﻿26 



BULLETIN 13*74, U. S. DEPABTMENT OF AGEICULTURE 



DISTANCE FROM COTTON FIELDS OF PREVIOUS YEAR 



On the Tlahualilo plaatation a system of rotation is practiced in 

 which cotton is not planted on the same land two consecutive seasons. 

 In addition a zoning system has been instituted providing the planting 

 of cotton in fields more or less distant from cotton fields of the previous 

 year. Studies were conducted in 1921 on the influence that distance 

 from source of infestation has upon the damage caused by the pink 

 bollworm. Regular boll examinations were made throughout the 

 season in four selected fields on the Tlahualilo property, located at 

 different distances from 1920 cotton fields. Data on this experiment 

 are given in Table 20. The four fields are hardly comparable in one 

 group, as fields Nos. 1 and 2 were west of old cotton fields and Nos. 

 3 and 4 were north. But field No. 1 is comparable with No. 2 and 

 No. 3 with No. 4. Only a slight advantage is shown for the more 

 distant fields. 



Table 20. — Pink bollworm infestation in 1921 fields located different distances from 



1920 fields 



[Worms per boll] 



Date 



Field 1 



(1,000 



meters)' 



Field 2 



(2,750 



meters)' 



Field 3 



(3,500 



meters)' 



Field 4 



(6,250 



meters)' 



June 23 _-. 



2 0.06 

 .01 



.008 

 .038 

 .47 

 .44 

 .54 

 1.74 



2 0.09 

 .015 

 .024 

 .006 

 .08 

 .15 

 .37 

 .80 





30 



0.575 

 .037 

 .05 

 .42 

 .45 

 .60 

 1.07 

 L74 



0.02 



July 8 



.002 



15 



.026 



22 - 



.23 



29 ..-. 



.35 



Aug. 5 



.61 



11 



1.12 



18 -- - 



1.69 



26-- 



2.84 



3.15 





Sept. 1 



3.55 



3.32 



9 



6.02 



4.50 





15 . - -. 



5.48 



4.34 











Averages . - 



1.35 



1.01 



L35 



1.17 







1 Distance from 1920 fields. 



2 Not included in average. 



In Table 21 the results of nonpickable cotton coimts made in 1921 

 at 47 different points in unirrigated fields on the Tlahualilo property 

 are presented with reference to the distance of these points from 1920 

 cotton fields. 



Table 21. — Percentage of nonpickable cotton, 1921, in unirrigated fields, ivith ref- 

 erence to distance from 1920 cotton fields 



Num- 

 ber of 

 points 



Distance from 1920 

 fields (meters) 



Percentage of cotton 

 nonpickable 



Average 



Range 



Average 



Range 



34 

 13 



680 

 4,730 



250-1, 500 

 2, 750-6, 250 



11.5 

 10.6 



3 to 32 

 7 to 16 



Here again only a slight advantage is shown in favor of the more 

 distant fields. Comparisons of individual fields in each group bear 



