100 MISC. PUBLICATION 6 2 6, U. S. DEPT. OF AGRICULTURE 



of leaf tier and leaf roller caterpillars. 

 It is prepared as follows: 



Large 

 Small quantities quantities 

 Derris powder (4 per- 

 cent rotenone) % ounce, or 4\i 9.5 ounces. 



level table- 

 spoonfuls. 

 Sulfonated castor oil ' 



(1-400) 1 fluid ounce, or 1 pint. 



2 tablespoon- 

 fuls. 

 Water 3 gallons. 50gallons. 



i Sodium oleyl sulfate or sodium lauryl sulfate may 

 be substituted for the sulfonated castor oil as a 

 spreader, but should be used according to the manu- 

 facturer's directions. White-oil emulsion (p. 100), 

 diluted to give 0.5 percent of oil in the spray water, 

 may also be substituted for the sulfonated castor oil. 



By adding 2 fluid ounces of an alco- 

 holic extract of pyrethrum (containing 

 about 2.4 percent of pyrethrins) to the 

 3-gallon derris formula, or 1 quart to the 

 50-gallon formula given above, the 

 effectiveness of the spray against thrips 

 and young caterpillars is greatly in- 

 creased. 



Home-Made Derris Dusts 



Efficient home-made dusts may be 

 prepared by mixing finely ground derris- 

 root or cube-root powder with various 

 diluents. These diluents should be non- 

 alkaline materials such as finely ground 

 tobacco dust, clay, kaolin, talc, wheat 

 flour, dusting gypsum, diatomaceous 

 earth, infusorial earth, and sulfur. When 

 mixing a derris or cube dust, follow the 

 procedure outlined for nicotine sulfate 

 dust (p. 98), except that lime should not 

 be used. 



To prepare a dust containing 1 per- 

 cent of rotenone, use the following 

 formula : 

 Derris powder (4 percent 



rotenone) 1 pound (1 part by 



weight). 



Diluent 3 pounds (3 parts by 



weight). 



To prepare a dust containing 0.5 per- 

 cent of rotenone, use the following 

 formula : 

 Derris powder (4 percent 



rotenone) Yi pound (1 part by 



weight). 



Diluent V/i pounds (7 parts 



by weight). 



If the rotenone content of the derris 

 powder is greater or less than 4 percent, 

 the proportions of the inert diluent must 

 be varied accordingly. For example, 1 

 part of derris powder containing 5 per- 

 cent of rotenone should be mixed with 4 

 parts of the diluent by weight to obtain 

 a 1-percent rotenone dust. Upon re- 

 quest, manufacturers of derris powders 

 will usually supply ground root of a 

 specified rotenone content, which can 

 then be diluted to the desired strength. 



Soap Sprays 



For such soft-bodied insects as 

 aphids and thrips and the young of scale 

 insects, mealybugs, whiteflies, and leaf- 

 hoppers, a concentrated solution of 

 ordinary soap may be employed with 

 some success as a spray. Such a solu- 

 tion may be prepared by dissolving 2 

 rounded tablespoonfuls of soap flakes, 

 or a 1-inch cube of laundry soap, or a 

 rounded tablespoonful of "whale-oil or 

 potash fish-oil soap, in 1 quart of hot 

 water. For seedlings and tender plants, 

 use only half the quantity of soap sug- 

 gested above, since such plants are 

 often injured if the full strength is 

 employed. The white coconut-oil soaps 

 are especially good as insecticides and 

 will work well in hard water. Soap 

 solutions are most effective when applied 

 on calm, humid days, when the rate of 

 evaporation is low. 



Soaps are also used to a large extent 

 in preparing emulsions, and also as 

 spreading and wetting agents and as 

 stabilizers for nicotine and pyrethrum 

 sprays. The amount of soap required 

 in a spray mixture is regulated somewhat 

 by water hardness. If used with lead 

 arsenate, some soaps may increase 

 arsenical injury to foliage. 



Oil Emulsions 



White-Oil Emulsion 



Oil sprays are applied to plants in the 

 form of a diluted emulsion, since the 

 undiluted oil cannot be used on plants 

 with safety. The so-called highly re- 

 fined, or white, oils are preferable for use 

 in horticultural sprays. White oils are 

 made by treating petroleum oils chemi- 

 cally to render them inert and less in- 

 jurious to plants. The medicinal white 

 oils are examples, although those used 

 for horticultural sprays are usually 

 thinner and lighter. The white-oil 

 emulsion concentrates, also called sum- 

 mer-oil emulsions, are available on the 

 market and have the consistency of 

 thin paste or mayonnaise containing 70 

 to 85 percent of oil. They contain an 

 emulsifier, such as soap, to make them 

 mix readily with water. These emul- 

 sion concentrates are diluted with water 

 so that the final spray contains from 

 0.5 to 1 percent of oil. A dilution to 

 give 2 percent of oil is sometimes used 

 on the hardier shrubs. These strengths 

 are tolerated by most plants, although 

 sweet peas, ferns, and certain tender 

 plants are readily injured. Such in- 

 jury may occur because as the water 

 evaporates the oil is left behind in a 



