DISINFECTANTS AND DISINFECTION. 187 



The bisulphide is also used to kill the yellow- jacket, which is very injurious 

 to fruit, also the root crown borer of the peach, and to disinfect grapevine 

 cuttings, etc., etc. 



b. Hydrocyanic Acid Gas. This is about the only gas which is powerful 

 enough to kill insects and yet not injure the foliage. It is used by covering 

 the tree, shrub or bush with a tent cloth or canvas which should be oiled to 

 keep in the vapor. The vessel containing the chemicals is placed underneath 

 Exposure of from thirty to fifty minutes is usually sufficient. About one 

 ounce of potassium cyanide to 150 cubic feet of space is required. 



The gas is extremely poisonous and is often destructive to foliage. It is 

 preferably applied at night as it is then less injurious to the foliage. 



C. Sprays and Washes. Plant pests are most generally destroyed by 

 spraying agents or washes. A wash is really a more liberal application of 

 the spray, the two being alike as to the results to be attained from their use 



For low plants the remedy can be applied by means of a sprinkling can 

 but the better method is to use some form of force pump with spray nozzle. 

 A good spray pump should maintain a uniformly constant as well as adequate 

 pressure, should be simple of construction, with all parts readily replaceable. 

 The nozzle should break up the stream into a fine mist. 



It is, of course, desirable to get as much as possible of the spray to remain 

 on leaf or stem and to have it evenly distributed. If put on too abundantly 

 the fine droplets or gobules on the leaf will run. together and roll off to the 

 ground. The nozzle must not be held near the plant to be sprayed in order 

 to get the disirable dew-like deposit on the leaf. 



For scale insects a thorough moistening is necessary, wetting the bark, 

 the scale and eggs. In order to accomplish this the nozzle must be held 

 close. 



The following table by Woodworth will indicate the method of preparing 

 and using the more important spraying solutions: 



The well known Bordeaux mixture, so extensively used as a spray and 

 wash is prepared as follows: 



Water, 50 gal. 



Copper sulphate, 6 Ib. 



Unslaked lime, 4 Ib. 



The adhesive properties can be increased by adding soft soap in quantity 

 equal to that of the copper sulphate. It is also advisable to dilute the mixture 

 for spring spraying. It is the most effective and perhaps the cheapest 

 fungicide that can be used. 



Aphides (plant lice) and similar plant parasites may also be destroyed 

 with weak solutions of alum (1.5 to 2 per cent.). Beetles may be killed by 

 sprinkling a mixture of equal parts of red lead, sugar and flour, near their 



