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either of these spray materials on the basis of their effectiveness. 
(1) Derris root powder in water. 
(2) Pyrethrum extract, or pyrethrum-derris extract combined. 
Relative effectiveness of dusts to specific cabbage insects 
Based upon the relative efficiency, at the dosages recommended herein, 
of each of .^secticides tested, against each of the principal species of 
cabbage worms present, experiments indicate: (1) That as a control for the 
imported cabbage worm, derris is more effective than pyrethrum, paris green, 
cryolite . or calcium arsenate; (2) that derris and cryolite are approximately 
aqual in effectiveness in controlling the cabbage looper, and that both mater- 
ials are more effective than paris green, pyrethrum, or calcium arsenate; 
(3) that derris and calcium arsenate are approximately equal in effectiveness 
in controlling the larvae of the diamond-back moth, while pyrethrum, cryolite, 
and paris green are relatively less effective for this species. 
Derris 
Derris dusts . — Derris dusts containing 0.5 to 1.0 percent of rotenone 
have given very promising results in four sections of the Central, Eastern, and 
Southern States. Satisfactory diluents for the derris root powder are such 
nonalkaline materials as finely ground tobacco dust, finely ground inert clay, 
talc, diatomaceous earth, infusorial earth, wheat flour, dusting gypsum, kaolin 
(china clay), and finely ground dusting sulphur. Some of these diluents have 
the advantage of being more economical in cost and more readily available in 
some sections of the country than in others. Indications are that derris re- 
tains its insecticidal value for a period of only approximately 1 week in the 
field, under favorable weather conditions, although further work must be done 
before definite conclusions can be reached upon this point. Satisfactory re- 
sults were also obtained with commercial dusts containing approximately 0.5 
percent of rotenone. 
The rotenone content of derris root varies, and purchases should be 
made on the basis of rotenone content, total extractives, and degree of fine- 
ness. For example, a derris root powder containing 4 percent rotenone should 
contain not less than 14 percent total carbon-tetrachloride or ether extrac- 
tives. In general, the total extract (either by carbon tetrachloride or ether) 
uld average approximately three and one-half times the rotenone content. The 
derris root powder should be of such degree of fineness that not less than 90 
percent of it will pass through a sieve having 20 meshes per linear inch, and 
all of the material (100 percent) should pass through a sieve having 80 meshes 
per linear inch. 
The rotenone content of the finished mixed dust depends, of course, 
on the quantity of diluent used as well as on the percentage of rotenone in the 
original material. Insecticide companies now sell high-grade, finely ground 
derris powder of specified rotenone content made by blending the various an- 
alyzed batches. 
