90 VEGETABLE GARDENING 



and the potato scab gnat. Both cold and hot water are 

 used in destroying plant lice, but hot water is far more 

 effective. Plants will stand water heated to tempera- 

 tures ranging from 125 to 180 degrees The hot water 

 treatment is especially desirable to check lice on a small 

 number of cabbage plants in the home garden. Pyreth- 

 rum or insect powder is also effectual in destroying some 

 insects by closing their breathing pores. It is generally 

 used as a powder, but may also be mixed with water and 

 applied as a spray. 



137. Bordeaux mixture. — Although other fungicides 

 are used sometimes in vegetable gardening, this is the 

 standard spray for the control of fungous diseases of 

 vegetables. The usual formula is : 4 pounds of lime, 4 

 pounds of copper sulphate (bluestone) and 50 gallons 

 of water. 



It is convenient to keep stock solutions of both the 

 bluestone and the lime. To make a stock solution of 

 bluestone, use 2 pounds of bluestone to the gallon of 

 water. The lime should be slaked and kept as a thin 

 paste. Both solutions should be covered to prevent 

 evaporation. For the formula stated, add 2 gallons of the 

 bluestone solution to 25 gallons of water and then in- 

 troduce the lime paste diluted with the other 25 gallons. 

 When insufficient lime is used there is danger of burn- 

 ing the foliage of many plants. To make certain of add- 

 ing enough lime the ferrocyanide test should be em- 

 ployed. This may be done as follows : Dissolve an ounce 

 of potassium ferrocyanide or yellow prussiate of potash 

 in a pint of water; place in a bottle and label "poison." 

 Stir lime solution into the diluted bordeaux mixture until 

 the ferrocyanide solution will not turn brown when a 

 drop or two is added from the bottle. It is always safer 

 to have an excess of lime. As bordeaux mixture deteri- 

 orates upon standing, it should be used promptly after 

 mixing. 



