46 BULLETIN 1473, U. S. DEPARTMENT OF AGRICULTURE 
RELATION OF SPACING TO WEEVIL RESISTANCE 
Plants that are left close together in the rows are reduced in size, 
principally through the suppression of vegetative limbs which arise 
from near the base of the main stalk (2). With vegetative growth 
restricted, more plants can be added to the row without injurious 
crowding, and a larger crop of bolls can be set early in the season. 
Reducing the size of the plants.is very important under boll-weevil 
infestation, as more sunlight is admitted to the row lanes throughout 
the day and the air allowed to circulate more freely through the field. 
With small plants and open lanes, the infested squares or young bolls 
that are shed fall on open sunlit earth which soon dries them out 
and either kills or greatly retards development of the immature 
weevils; but, with large plants and heavily shaded lanes, the condi- 
tions are much more favorable to weevil development. The mortality 
of immature weevils under the intense heat of the sun on the hot 
earth of a row lane without shade is undoubtedly much higher than 
under more humid and shady conditions obtained in rows with wider 
spaced and more luxuriant plants. 
Hunter and Pierce (6) report the mortality of weevils at immature 
stages from heat and dryness as averaging 23.8 per cent for given 
dates from May to October. Smith (9) adds that, if counts were 
extended over the entire period from egg to adult, this figure might 
be trebled. The same writer submits evidence to show that the 
mortality of the immature weevils will run as high as 91.3 per cent 
under hot, dry conditions in Florida. This figure might often be 
exceeded in the drier districts of Texas. 
Since heat and dryness play so important a part in the control of 
the boll weevil, a very practicable and economical contribution toward 
control is put into operation by restricting the growth of the cotton 
plant and allowing an abundance of sunlight to fall in the row lanes 
throughout the day. Also, the more compact rows with closely spaced 
plants can be much more effectively and efficientiy poisoned with 
improved dusting machinery than can the larger branching type of 
plants. 
Early maturity is another important factor under weevil conditions. 
By suppressing the lower limbs, which do not directly produce bolls, 
early maturity of the crop is favored. The fact that successive fruit- 
ing branches are formed in about one-third of the time that succes- 
sive squares appear on fruiting branches accounts for more rapid 
fruiting in a vertical series along the axis of the plant than in a hor- 
izontal series along the fruiting branch (7). An early crop of cotton 
is produced largely from bolls at the first nodes of the primary fruit- 
ing branches, not on the limbs or vegetative branches. In fact, it is 
not possible to produce an early crop of cotton on large, luxuriant 
plants. 
CONCLUSIONS 
The spacing experiments discussed in this report extend over a 
period of five years, from 1921 to 1925, inclusive, and include many 
repetitions. ‘The combined results show larger yields from the closer 
spacings and indicate that cotton plants generally are left in the fields 
at distances too far apart to obtain the best yields. ‘The five sum- 
mers during the progress of the experiments reported herein were dry 
to extremely dry, and it is recognized that under more humid condi- 
tions the behavior of the spacings might be somewhat different. 
