HANDBOOK OX INSECT ENEMIES OF FLOWERS AND SHRUBS 99 



dust, fine dusting sulfur, pyrophyllite, 

 or talc. A manufactured dust^ contain- 

 ing 0.3 percent of pyrethrins is recom- 

 mended for general purposes. 



Since pyrethrum products lose their 

 strength rapidly on exposure to the air, 

 they should be kept in tight containers 

 and not mixed until ready to be applied. 

 It may be safely applied to most garden 

 flowers without causing injury. Usually 

 the effectiveness is increased by adding 

 a suitable wetting or spreading agent 

 (p. 103) to the spray; however, many 

 commercial brands already have these 

 materials included. Pyrethrum may be 

 combined with derris or cube, as dis- 

 cussed under Derris (p. 99), and the 

 combination makes a more effective 

 spray against both chewing and sucking 

 insects. 



Caution. — Although pyrethrum is 

 comparatively nonpoisonous to human 

 beings and other warm-blooded ani- 

 mals, persons allergic to ragweed in 

 some instances are subject to attacks 

 of hay fever when exposed to pyrethrum. 



Derris, Cube, and Other Rotenone 

 Insecticides 



Derris and cube powders are made by 

 grinding the roots of certain tropical 

 plants which contain rotenone and other 

 ingredients that kill various insects. 

 They are largely used as contact insec- 

 ticides, although against some insects 

 they seem to act as stomach poisons or 

 repellents. These materials are effec- 

 tive against such sucking insects as 

 aphids and thrips, and such chewing 

 insects as young caterpillars, the cabbage 

 looper, the imported cabbage worm, the 

 European corn borer, ants, young saw- 

 fly larvae, and the adults of the Japa- 

 nese beetle, cucumber beetles, and flea 

 beetles. When used with sulfonated 

 castor oil or in white-oil emulsion, they 

 are effective under greenhouse condi- 

 tions against the common red spiders 

 and other spider mites. 



The rotenone content of these ma- 

 terials varies considerably, but a good 

 derris-root or cube-root powder should 

 contain from 4 to 5 percent of rotenone 

 and about 3V<> to 4 times as much of other 

 extractives. The dust may be stirred 

 into water and applied as a spray, or 

 mixed with some other fine dust for 

 dusting infested plants. For sprays 

 the final rotenone content usually ranges 

 from 0.0056 to 0.025 percent, and for 

 dusts from 0.5 to 1.0 percent. These 

 may be prepared at home, as described 



below, or the commercially prepared ma- 

 terials ready for use may be purchased. 

 Liquid extracts of the active ingredients 

 i are also available; however, certain of 

 these may lose some of their effective- 

 ness when mixed with water. The 

 derris and cube insecticides are sold 

 under various trade names, and since 

 the strength of the active ingredients 

 may vary in the different brands, they 

 should be used as directed by the manu- 

 facturer. 



Rotenone-containing insecticides lose 

 their strength on exposure to sunlight 

 and air, and several days after being 

 applied to a plant they are usually no 

 longer effective. All materials should 

 therefore be stored in tight containers, 

 and sprays or dusts should be prepared 

 just before they are to be used. 



Caution — These insecticides are com- 

 paratively nonpoisonous to man and 

 other warm-blooded animals, although 

 sometimes they do irritate the tender 

 skin and mucous membranes. 



Home-Made Derris Sprays 



For the control of cabbage worms, leaf 

 tiers, leaf rollers, and similar caterpillars, 

 and for the spotted cucumber beetle and 

 other cucumber beetles, use a spray 

 made by mixing 2 or 2 l A ounces of derris 

 powder, having a rotenone content of 4 

 percent, in 3 gallons of water, or 2 or 2 l / 2 

 pounds in 50 gallons of water. These 

 proportions give the spray a rotenone 

 content of about 0.02 or 0.025 percent. 

 (See table 1 for methods of preparing 

 different quantities from various 

 strengths of derris or cube, page 105.) 



To prepare a spray, first wet the derris 

 powder with a small quantity of water, 

 preferably containing a suitable wetting 

 or sticking agent. Mix thoroughly to 

 make a uniform paste. Then stir this 

 paste into the bulk of the water in the 

 spray tank. 



Derris sprays are improved by the 

 addition of a nonalkaline spreader or 

 sticker, such as high-grade liquid or 

 powdered neutral coconut-oil soap, 

 miscible pine oil, one of the sulfonated 

 oils, or one of the proprietary materials 

 now available. These should be used 

 according to the dilutions recom- 

 mended by the manufacturer. 



A derris spray considerably weaker 

 than the formula above, and containing 

 0.0056 percent of rotenone, is effective 

 against the common red spiders and 

 other spider mites, the cyclamen mite, 

 certain thrips. and the very young stages 



