COTTON IN WEEVIL-CONTROL EXPERIMENTS 



3 



even when surface moisture becomes deficient. June was very dry, 

 with only 0.55 inch of rain. Precipitation during the growing period 

 of cotton was fairly well distributed, but effective rains fell on only 

 six days between May 30 and September 7. 



Maximum temperatures during June, July, and August were 

 comparatively high, and the long periods of hot weather between the 

 few good rains resulted in droughty conditions in spite of the appar- 

 ently adequate precipitation. 



The average monthly maximum and minimum temperatures and 

 the monthly precipitation for the season of 1923 are given in Table 1. 



Table 1. — Average minimum and maximum temperatures and monthly precipita- 

 tion at San Antonio, Tex., from April to September, 1923 



Items of comparison 



Jan. to 

 Mar. 



Apr. 



May 



June 



July 



Aug. 



Sept. 



Average temperature (° F.): 





59.3 



77.6 



2.93 



3.11 



64.5 

 89.0 



1.67 

 3.09 



72.4 

 95.4 



.55 

 1.88 



71.2 

 95.3 



3.77 

 2.12 



72.4 

 97.8 



2.50 

 1.87 



70.7 







89.4 



Precipitation (inches): 



1923. 



9.27 

 3.98 



3.02 



Average, 1907 to 1920 



2.57 



Favorable conditions for the hibernation of boll weevils in the San 

 Antonio district are afforded by scattered areas of undeveloped land 

 covered with mesquite and huisache trees and by large fields of 

 Johnson grass. A heavy infestation from overwintered weevils 

 usually occurs in cotton planted in this section. The first new genera- 

 tion of weevils usually appears before the first of July. 



Periods of dry weather often restrict the growth of the plants, and 

 the shed squares are exposed to direct sunlight, so that a natural 

 control of the weevils may result from destruction of the larval and 

 pupal stages in the fallen squares. When heavy rainfalls occur 

 during the early stages of plant growth, excessive vegetative develop- 

 ment of the plants results, so that the weevils have more protection 

 even though there is dry weather later in the season. There is 

 slight possibility of effective natural control when the plants grow 

 large and the lanes between rows are shaded so as to protect the 

 infested squares. 



In the season of 1923 weevils were first found on May 28. Squares 

 were very small at that time, but by the first week in June numerous 

 punctured squares could be seen in all cotton which had reached the 

 fruiting stage. Dry weather throughout the greater part of May 

 and June retarded the growth of the plants. This small size kept 

 the lanes open between the rows and afforded favorable conditions 

 for natural control of weevils by exposing the fallen squares to direct 

 sunlight. Nevertheless, the weevil infestation increased slowly, until 

 by the first of August there were enough weevils to destroy practically 

 ail of the squares. 



COMPARISON OF SUCCESSIVE ADJACENT PLANTINGS AT SAN 



ANTONIO 



At San Antonio the successive plantings were made on April 19 

 and 28 and May 5 and 12. The I. one, Star variety was used, the seed 

 having been grown on the experiment farm in 1922. The rows were 



