PESTS AND DISEASES OF PLANTS 225 



A more durable weatherproof whitewash is prepared as follows : 



(1) Quick lime 62 pounds 



Water (hot) 12 gallons 



(2) Common salt 2 pounds 



Sulphate of zinc 1 pound 



Water ( boiling) 2 gallons 



(3) Skimmed milk 2 gallons 



Slake the lime thoroughly in (1) ; dissolve the salt and sulphate of 

 zinc in two gallons of water (2) ; pour (2) into (1) and add (3). Mix 

 thoroughly. Two pounds of flour paste (dissolved in two gallons of hot 

 water) may be added instead of the skimmed milk. 



FUMIGATION. 



Fumigation consists in the generation and uses of gases to kill pests. 

 Formerly such practices were limited to the uses of carbon bisulfid, sulphur 

 dioxid and tobacco fumes. The use of hydrocyanic acid gas in citrus 

 orchards has lately been so perfected as to become of very great import- 

 ance and has opened up a remarkable field in the control of orchard pests. 



Carbon Bisulfid. 



Carbon bisulfid is a liquid which evaporates into a heavy, highly in- 

 flammable and explosive gas. It was first used for fumigating beans, 

 grains or cereals for weevils, and is still a very efficient method of con- 

 trolling such pests. In handling the liquid great care should be taken to 

 keep it away from a flame on account of the vapor being highly explosive. 



For Storehouse Pests. Before fumigation is begun care should be 

 taken to see that the room or container is made as tight as possible. The 

 temperature should be 70 degrees Fahrenheit or above, for poor and 

 unsatisfactory results are sure to follow even excessive doses at a lower 

 temperature. In a tight compartment five pounds of carbon bisulfid to 

 every 1,000 cubic feet of air space will give excellent results in killing 

 weevils. If the compartments can not be made tight, increase the amount 

 of the fumigant. 



For Root Pests. Carbon bisulfid has also been used in the fields to 

 kill root pests like the woolly apple aphis, black peach aphis, grape 

 phylloxera, white grubs, root-maggots, but is far too expensive to be 

 practical and is effective only in soils of just the right degree of porosity. 

 For a small plant, a hole is made in the ground near the base and a tea- 

 spoonful of the liquid poured into the hole, which is covered to prevent 

 surface evaporation. For larger plants several holes are made deep enough 

 to allow the vapor to disseminate around the infested roots. A syringe- 

 like instrument is sometimes used to inject the liquid into the soil around 

 the roots of the infested plants. In all such work care must be exercised 

 in making the applications or the plants may be killed by an excessive dose 

 or by the carbon bisulfid coming in direct contact with the roots. 



For Wood-Borers. Carbon bisulfid is also injected into the burrows 

 of wood-boring insects with some success, but this method has never met 



