RED SPIDER ON COTTON. 9 
and tedious hoeing method. (See fig. 7.) It must be remembered, 
however, that sodium arsenate is a poison, and care should be taken 
to prevent horses and cattle from grazing on treated weeds. 
SPACING, 
Some have claimed that infestation spreads through a field only by 
means of the interlacing cotton branches, and that by increasing the 
spacing the spread of the red spider can be prevented. Since it is 
now known, however, that the mites commonly travel on the ground 
also, from plant to plant, it is easily seen that wide spacing of cotton 
plants will by no means entirely prevent the spread of the pest. 
MAINTAINING MULCH. 
By maintaining continually in fields a finely pulverized surface 
mulch the progress of migrating mites is somewhat retarded and the 
development of infestation correspondingly discouraged. The plant- 
ing of cotton by the checking system permits the cultivation of each 
plant on four sides and is a good method from the viewpoint of the 
control of the red spider. 
ROTATION, 
Since the wild grasses and small grains appear to be about the only 
plants which are free from red-spider attack, there is little in the way 
of immune crops which can be used for the purpose of rotation. 
Furthermore, provided the sources of infestation were allowed to 
remain, the pest would surely reinvade fields, upon the return to 
cotton, even should the small grains or grasses be planted for a time. 
FERTILIZERS. 
Although the fertilizing of cotton land in no way discourages the 
development of red spiders, yet the judicious use of fertilizers in- 
vigorates the plants so that they are better fitted to overcome the 
injury. 
REPRESSIVE MEASURES. 
Under the heading “ Repressive measures” may be discussed those 
measures which can be taken to combat the pest when it has gained 
entrance to cotton fields. It has been demonstrated that it is possible 
to eradicate the pest from infested fields. . 
By keeping a constant watch of cotton fields the earliest affected 
stalks may be detected and destroyed. In this method it is usually 
necessary to repeat the operation several times, since certain plants 
