﻿STUDIES OF THE PINK BOLLWOEM IN" MEXICO 



23 



point of note is the effect an infestation by the boll weevil has on the 

 percentage of nonpickable cotton. This insect severely damaged 

 several fields in 1921. When the attack occurs reasonably early and 

 the weevil becomes abundant, it destroys the greater part of the late 

 crop, allowing very few late bolls to remain on the plant. Then we 

 have a condition represented by a short early crop only slightly 

 damaged by the pink boUworm and very little nonpickable cotton on 

 account of the lack of late bolls. This occurred in the case of planta- 

 tion No. 19 in 1921, where the percentage nonpickable in the unirri- 

 gated field is tmce as great as in the irrigated. 



RELATION OF THE AMOUNT OF NONPICKABLE COTTON TO TOTAL DAMAGE 



A seasonal variation in the ratio of nonpickable cotton to total 

 damage may be looked for, because in seasons of high prices for the 

 stajple it will be picked cleaner than when low prices prevail. This 

 variation was illustrated in 1921 and 1922. The infestation on the 

 Tlahualilo plantation, as shown in Table 18, was equally as high in 

 1922 as it was in 1921, but the percentage of nonpickable cotton on 

 this plantation (No. 31), as shown in Table 17, was 16.1 for 1921 

 and 9.96 for 1922 (taking the average of the irrigated and'unirri- 

 gated fields). About the only explanation for this great difference 

 IS that the cotton was more closely picked in the latter season, a 

 greater percentage of the severely damaged cotton being gathered 

 and less "nonpickable" cotton left in the field. The price of picking 

 at the end of the season and the price of low-grade cotton apparently 

 substantiate this theory. The lowest grade of cotton (good ordinary) 

 sold for 10 cents per pound during the 1921 season and for 15 cents 

 per pound (Mexico City prices) during the 1922 season. At the 

 same time the highest price paid for picking at the end of the season 

 was 4 cents per kilo in 1921 and 6 cents per kilo in 1922. In this 

 connection is presented Figure 9 to show the relation between non- 

 pickable cotton and the price of cotton. 



Table 18. — Progress 



of infestation 



of green bolls, 

 1922 



Tlahualilo plantation, 1921 and 



Month 





Week 



Percentage of bolls 

 infested v 



Number of worms 

 per boll 





1921 



1922 



1921 



1922 





Third 







22.6 



7.3 



5.2 



4.9 



16.3 



15.8 



27.6 



31.1 



59.0 



84.1 



99.3 



99.9 



100 



100 



100 



100 



100 



100 



100 

 99.2 



100 



100 



100 





0.22 





Fourth... 









.08 



July 



First 









.06 



Second 





17 



29 



32.1 



34.3 



43.7 



08.3 



87.9 



96.4 



95.5 



99.1 



99.3 



100 



100 



100 



100 



0.19 



.45 



.48 



.54 



.72 



1.57 



2.46 



3.42 



4.03 



4.36 



5.25 



5.82 



5.84 



0.98 



4.05 



.06 





Third -.- 





.23 





Fourth... 





.20 



August. .. 



First 





.37 









.48 





Third ... 





1.05 









2.47 





Fifth ... 





5.13 



September 







0.48 









7.15 





Third.... 





7.16 









0.13 



October 



l''irst ... 





8 57 





Second 





7.48 





Third 





5.87 





Fourth... 





4.97 



November . . 



' First 









4.42 













3.16 





Tliird 









5.26 





I'Vjiirth 









5.62 





1 











