264 ELEMENTS OF AGRICULTURE 



If much spraying is to be done, a stock solution will 

 save time. For this, fill a barrel with water and weigh out 

 one pound of copper sulfate for each gallon. Suspend 

 this in a bag in the top of the barrel and it will all dissolve. 

 Instead of weighing it for each tank of spray, we can then 

 take out as many gallons as we desire pounds. Two pounds 

 may be dissolved in each gallon, if desired. 



The lime may also be slaked in quantities. The lime 

 settles, and we cannot be sure when we have enough by 

 measure, so that if we use a stock solution of lime we should 

 also use the potassium ferrocyanide test. This is desirable, 

 anyway. Potassium ferrocyanide makes a yellow solution. 

 If a drop of it is added to a solution of copper sulfate, it 

 turns a brick-red. If lime enough is first added to neutralize 

 the copper sulfate, the drop remains yellow. About a 

 half more lime is usually added after the copper has been 

 neutralized. 



For spraying small gardens, stock solutions may be 

 kept in large bottles and the proportionate amounts used. 



239. Poisons. Paris green and arsenate of lead are the 

 most common poisons. Five ounces to a pound of Paris 

 green are used in fifty gallons of spray. Or one to four 

 pounds of arsenate of lead may be used. The arsenate of 

 lead never hurts the foliage, so that it may be used in any 

 strength. Paris green sometimes causes injury if used 

 too strong, or if used without lime. Paris green is also 

 used to dust on plants, either alone or with lime. 



240. Contact Remedies. The chief use of contact reme- 

 dies is to kill the San Jose scale. For this purpose, the 

 trees must be sprayed while dormant, because any spray 

 that is strong enough to kill the scale will also kill the leaves. 



