654 IOWA DEPARTMENT OF AGRICULTURE. 



for delicate plants. Besides being the least injurious, lead arsenate 

 has the advantage of adhering better than other arsenicals. It may- 

 be bought in powdered form as disparene ready to use, the same as 

 Paris green. As it has a tendency to lose its strength in powdered 

 form, it is much better prepared when used at once. It is then also 

 more finely divided and can better be distributed over the plant. Lead 

 arsenate is thrown down as a whitish flocculent precipitate upon pouring 

 together clear solutions of lead acetate (sugar of lead), 131/2 cents 

 per pound, and sodium arsenate, 20 cents per pound. The lead and 

 sodium exchange places, forming the insoluble poisonous lead arsenate 

 and sodium acetate. This latter compound is entirely harmless to 

 plants, as is also lead acetate. It Is very important that an access of 

 tMs be used to be sure that none of the arsenate remains in combination 

 with the sodium in which form it Is soluble. The proportions usually 

 given are twelve ounces of lead acetate to four ounces of sodium arsen- 

 ate, which insures an access of the former. These amounts are sufficient 

 for from fifteen to fifty gallons of spray. Fifty gallons of spray will cost 

 at retail prices about 45 or 50 cents for the chemicals; at wholesale, 15 

 cents. 



Each of the two chemicals should be dissolved separately, then 

 poured together. Arsenite of soda is the chiefest of the arsenicals. It 

 is prepared by boiling together for fifteen minutes or more one-half pound 

 white arsenic, two pounds sal soda and two quarts of water. This 

 equals one pound of paris green. Vessels used in its preparation should 

 not be used for other purposes as they are very poisonous. This mix- 

 ture is perfectly soluble, hence unsafe to use unless added to Bordeaux 

 mixture or mixed with lime. Two pounds of lime are required for the 

 above named amounts and is better boiled for fifteen minutes. Where 

 Paris green is used from six ounces to one pound required for fifty gal- 

 lons of water, the proportions depending upon the insect for which 

 it is used. The other class of poisons consists of various oils and 

 various caustic preparations which kill the insects by contact. They are 

 more likely to be more injurious to the plants and diflBcult to apply. 

 Their chief use is against insects like scales, plant lice, and other true 

 bugs, all of which have sucking mouth parts. Since they eat none 

 of the surface but only suck the juices, they can not be poisoned with 

 arsenicals. For the scale insects the lime-sulphur wash is considered 

 best. (For winter use only it destroys all eggs or spores of any dis- 

 ease with which it comes in contact, and trees so treated have bright, 

 healthy appearance throughout the season.) Directions for preparing it 

 may be found in the spraying calendar issued by the experiment station 

 at Ames and sent to those asking for it. Kerosene emulsion, or whale 

 soap, is commonly used for plant lice, or for summeh treatment of scales 

 or similar insects. Kerosene emulsion is made by dissolving one-half 

 pound of Ivory soap in one gallon of hot water, add two gallons of 

 kerosene and churn until a creamy emulsion is formed. This should be 

 diluted fifteen or twenty times for growing trees. Small trees infested 

 with colonies of plant lice in the tops can be easily treated by bending 

 over the limbs and dipping them in a strong tobacco decoction, made by 

 boiling one pound of tobacco stems in two gallons of water. Formulae 



