﻿38 



BULLETIN 1374, U. S. DEPARTMENT OP AGRICULTURE 



district (fig. 2, p. 3), whereby the fields remain under water for 

 periods varying from one to two months and sometimes longer, 

 will kill very nearly all the resting larvae in the soil and in bolls on the 

 surface. The flooding of heavily infested cotton fields just cleared, 

 whenever it can be practiced, should materially retard the infestation 

 infnev/ cotton. 



WINTER PLOWING 



To determine the effect of winter plowing on resting larvae in the 

 soil, an experiment was conducted in 1922 in which plats in a field 

 that was heavily infested with the pink bollworm late in the fall of 

 1921 were plowed in different ways. Five quarter-acre plats were 

 laid off and the following treatments given: 



Plat 1: Uncultivated. 



Plat 2: Harrowed and cross-harrowed with disk harrow, March 9, 1922. 



Plat 3: Plowed to a depth of about 6 inches, harrowed and cross-harrowed 

 with disk harrow, March 9, 1922. 



Plat 4: Plowed to a depth of 6 inches, March 9, 1922. 



Plat 5: Zoca, soil thrown away from plants with two cultivator shovels, 

 first week of April, 1922. 



After this plowing, examinations of 1 square yard of soil to the 

 depth of about 8 inches were made in each of these plats at intervals 

 of about 20 weeks. Plat 5 was not included in the first examination, 

 as it had not then been cultivated. The data obtained in this 

 experiment are given in Table 29. 



Table 29.- 



-Effect of different methods of plowing on the pink bollworm hibernating 

 in the soil 





Number of pink boUworms found per square yard of soil 



Date examined 



Platl 



check 



Plat 2, har- 

 rowed 



Plat 3, plowed 

 and harrowed 



Plat 4, plowed 

 only 



Plat 5, culti- 

 vated 





Living 



Dead 



Living 



Dead 



Living 



Dead 



Living 



Dead 



Living 



Dead 



1922 

 Mar. 22.. 



10 



18 

 8 

 7 

 4 

 2 

 

 

 

 



5 



7 

 14 

 7 

 

 3 

 1 

 

 

 



4 



13 

 7 

 5 

 1 

 2 

 

 

 

 



11 



7 

 2 

 4 

 4 

 2 

 3 

 

 

 



3 



1 

 13 

 7 

 6 

 2 

 4 

 

 

 



6 



1 

 3 



5 

 7 

 4 

 3 

 

 1 

 



16 



9 

 6 

 3 

 5 

 2 

 

 

 

 



11 



2 

 

 3 

 

 1 

 1 

 

 



1 



No € 



xamina- 



Apr. 17 



tion. 

 2 



1 



May 1 



8 

 

 



1 

 4 

 

 

 



1 



17 



2 



30 



1 



June 12 



3 



26 







July 10.-.. 







24 







Aug. 8 











Total 



49 

 4.9 



37 

 3.7 



43.0 



32 

 3.2 



33 

 3.3 



50.77 



36 

 3.6 



30 

 3.0 



45.5 



41 

 4.1 



19 

 1.9 



31.7 



15 

 1.67 



8 



Average 



Percentage 

 dead 



.89 

 34.8 











Considering only the total number of living individuals found per 

 plat, there is a notable reduction in the plowed plats, especially the 

 cultivated zoca. But the two harrowed plats show the highest 

 percentage of dead individuals, and plat 4 is particularly low in this. 

 Considering the individual examinations, the first one shows a very 

 decided advantage for the two harrowed plats. Only 4 and 3 living 

 specimens were found in these, compared with 10 in the uncultivated 



