SPRAY MATERIALS 139 



The white hellebore and the pyrethrum lose their poisonous 

 properties quickly when exposed to the air. These insecti- 

 cides are poisonous to insects but not to higher animals. 

 They are valuable to use on ripening fruit or just before the 

 harvesting of such crops as the lettuce or the cabbage. These 

 poisons must be strictly fresh or they are worthless. 



Poisons for Sucking Insects. — Sucking insects cannot be 

 controlled by the same poisons as biting insects, because 

 these insects do not eat the plant tissue. The mouth parts 

 of the sucking insects are so constructed that the insect can 

 insert them into the plant tissue and suck out the plant juices, 

 and therefore any stomach poison applied to the plant will 

 in no way affect the sucking insects. In order then to con- 

 trol this class of insect pests, we must spray the plant and 

 cover the insects with some material that will destroy them 

 by coming in contact with their bodies. A few common 

 contact insecticides are lime sulphur, nicotine sprays, various 

 mixtures of soap and kerosene and oil sprays. 



FORMULAS FOE CONTACT POISONS. 



Lime-sulphub Wash. 

 Stone lime .... . . . 12 to 15 pounds 



Flowers of sulphur . .15 pounds 



Water . 50 gallons 



This formula is for the home-made wash. Slake the lime 

 in a small quantity of water. Gradually stir the sulphur 

 into this mixture. Dilute the mixture to 12 gallons and boil 

 for one hour or longer. Remove from the fire and add enough 

 water to make 50 gallons. Strain the wash through a fine- 

 mesh strainer. This spray must be used when the plants are 

 dormant, and it is either applied in the spring before the buds 

 open or in the fall after the leaves drop. The chief disad- 

 vantage of this, home-made wash is the great quantity of 

 sediment which is hard to remove satisfactorily so that it 

 will not clog up the pump and nozzles. 



COMMERCIAL LIME-SULPHUR SOLUTION. 



The commercial lime-sulphur is much easier to use because 

 it is free from sediment and requires no preparation other 



