Numerous other materials are sometimes used in arresting the ravages of injurious insects. Lime, ashes, bordeaux mixture and sulphur may be classed among insect repellents. A formalin solution prepared by mixing I pint of a 40 per cent solution with 30 to 40 gallons of water is valuable in treating potatoes both for scab 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 temperatures 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.
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 introduce the lime paste diluted with the other 25 gallons. When insufficient lime is used there is danger of burning the foliage of many plants. To make certain of adding enough lime the ferrocyanide test should be employed. 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 deteriorates upon standing, it should be used promptly after mixing.
It is difficult to cause solutions or mixtures to adhere to the leaves of some plants; for example, the onion and cabbage. To obviate this trouble, a "sticker" may be made of 2 pounds of resin, 1 pound of sal soda crystals and 1 gallon of water. This mixture is boiled out of doors from 1 to 1 1/2 hours, or until the solution is of a clear brown color, and then added to every 50 gallons of bordeaux mixture and to every 100 gallons of other spray materials.