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In the interests of the industries concerned, it is strongly urged that 
the growers be warned of the poisonous nature of arsenicals and similar mate- 
rials and that they take special precautions to be certain that such materials 
do not remain on the marketed product. 
From the evidence at hand, the compounds of derris, cube, and pyrethrum, 
when applied at the dosages recommended herein, should not leave harmful 
residues on the market product. The active principles of these materials are 
rendered inert within a comparatively short time through the action of sunlight 
and exposure to the air, especially when spread thinly over the plants. 
CABBAGE WORMS ON CABBAGE 
As a general recommendation for the control of the imported cabbage 
worm, the cabbage looper, and the diamond-back moth on cabbage, the following 
materials (as dusts) are recommended in the order listed, at the dosages 
detailed later in this circular. 
Materials for dusts 
(1) Derris, 
(2) Pyrethrum, 
(3) Paris green, cryolite, calcium arsenate. 
The dusts containing these materials should be applied in such a manner 
as to cover all infested portions of the plant, care being taken to reach the 
insects whenever possible. The rate of application may vary according to the 
size of the plants. Applications of 15 to 20 pounds per acre, per application, 
of the dust mixtures discussed later have given satisfactory results. Applica- 
tions should be made in accordance with the more specific recommendations that 
follow; they should begin when the worms first appear and be repeated as often 
as necessary to protect the crop. 
It is essential that the insecticides be applied when the worms are 
small, as the larger ones, especially the cabbage looper, are usually more 
difficult to kill. Furthermore, it is essential that the worms be killed 
before they have caused appreciable injury to the plants. 
NOTE: Paris green, cryolite, and calcium arsenate should not be used 
on any portion of the cabbage plant that is to be marketed. This means that 
cabbage intended for marketing as U. S. Grade No. 1 (which allows four loose 
outer leaves) should not be poisoned with these materials after the head be- 
gins to form. If the marketed product is to bear a greater number of loose 
outer leaves than those allowed in the above grade, these materials should 
not be used after the plants have been thinned or transplanted. 
Materials for sprays 
In general, dusts have given better results than sprays in cabbage 
worm control. If desirable to use a spray, the following materials are recom- 
mended. Experiments to date have not indicated any special preference for 
