18 MISC. PUB. 52 6, U. S. DEPT. OF AGRICULTURE 



deciduous foliage do not follow a sulfur spray with sprays contain- 

 ing oil until all sulfur residues have disappeared. 



Directions for the preparation of self-boiled lime and sulfur and 

 home-boiled lime-sulfur concentrate may be obtained from the county 

 agricultural agent, the State experiment station or State entomologist, 

 or the United States Department of Agriculture. 



Caution. — Lime-sulfur sprays are very caustic to the skin, espe- 

 cially at the strengths used in the dormant season. Persons ex- 

 posed to this material should protect their faces by covering them 

 with grease or vaseline before they begin spraying, and should 

 avoid getting any of the material into the eyes, where it will cause 

 acute temporary discomfort. Don't allow lime-sulfur spray to 

 drift onto painted buildings, or a very unsightly stain may result. 



MAGNESIUM ARSENATE 



Several compounds of magnesium oxide and arsenic oxide are 

 known, and it has been reported that the commercial product 

 sold as "magnesium arsenate" contains the dimagnesium salt, 

 MgHAs0 4 , and two basic salts, principally one having the composition 

 Mg 3 ( As0 4 ) 2 .MgO.H 2 0. There is also present a large excess of magne- 

 sium oxide or hydroxide, which is necessary to keep down the content 

 of water-soluble arsenic. 



Magnesium arsenate is a white powder but is colored pink when 

 packaged as an insecticide to indicate its poisonous nature. It is used 

 as a spray, at the rate of 4 pounds in 100 gallons of water, against the 

 Mexican bean beetle. Derris and cube have largely replaced it for the 

 control of this insect, but it can be used where these are not available, 

 provided application is discontinued when the bean pods start form- 

 ing. Magnesium arsenate is not used for the control of other insects. 

 Its tendency to injure foliage is one drawback to its extensive use. 



Caution. — Magnesium arsenate, like all arsenicals, is a poison- 

 ous compound and should always be so labeled, and stored away 

 from all food products and out of the reach of children. For 

 spray-residue tolerance, see page 3. 



MERCURIC CHLORIDE 



Mercuric chloride (HgCl 2 ) is known also as corrosive sublimate and 

 as bichloride of mercury. It is soluble in water, although it dissolves 

 in cold water very slowly. Commercially it is available as a white 

 powder, as crystals, or in the form of 7.5-grain tablets. The powder 

 form is used commonly for insecticidal purposes. 



A solution of 1 ounce in 7y 2 gallons of water or 1 level teaspoonful 

 in 10 quarts of water, or two 7.5-grain tablets to 1 quart of water 

 (1 : 1,000) is prepared by dissolving the compound in a small quantity 

 of hot water and diluting it with cold water. This solution is used in 

 the control of fungus gnats, earthworms in greenhouses, and the cab- 

 bage root maggot. To avoid injury to the plant, keep the solution off 

 of the foliage. Mercuric chloride is also used for the treatment of 

 dormant gladiolus conns to control the gladiolus thrips. Other 

 common uses are as a fungicide and a germicide. 



