The most important contact insecticides are soaps, sulfur, sulfur compound, and oily or resinous emulsions.

Soaps

The most commonly used soap solution is that prepared from fish-oil soap. The commercial brands of this soap are usually by-products and contain many impurities; further, many of them contain an excess of free or uncombined alkali and are thus likely to injure young and tender foliage. A good fish-oil soap may be prepared by the following formula: Caustic soda, six pounds; water, one-half gallon; fish-oil, twenty-two pounds. Dissolve the caustic soda in the water and then add the fish-oil gradually under constant and vigorous stirring. The combination occurs readily at ordinary summer temperatures, and boiling is unnecessary. Stir briskly for about twenty minutes after the last of the oil has been added. There is now on the market a good brand of insecticide soap prepared from cotton-seed oil soap stock or from an impure grade known as pancoline.

Sulfur

Sulfur may be obtained in two forms, - flowers of sulfur and flour of sulfur. In the form of a powder or dust, sulfur is especially valuable against red-spider. In California, flowers of sulfur mixed with equal parts of hydrated lime is blown on the trees for the control of red-spider and mite. It may also be used for the same purpose mixed with water at the rate of one pound in three gallons of water, to which has been added a little soap to keep the sulfur in suspension. The mixture should be agitated constantly during spraying. The sulfur remains longer m suspension if it is first made into a paste with water containing one-half of 1 per cent of glue. Page 1028.

Lime-Sulfur Solution

A solution of lime-sulfur was first used as an insecticide in California in 1886. It is now the standard remedy for blister mite, San Jose' scale and similar scales, as well as an efficient fungicide. The lime-sulfur solution may be purchased in the concentrated form or may be prepared as follows: Lump lime (95 per cent calcium oxid), thirty-eight pounds; lump lime (90 per cent calcium oxid), forty pounds; sulfur, eighty pounds; water, fifty gallons. Make a paste of the sulfur with about ten gallons of hot water. Add the lime. As the lime slakes, add hot water as necessary to prevent caking. When the lime has slaked, add hot water to make fifty gallons and boil one hour, stirring constantly. Water should be added from time to time to keep the liquid up to fifty gallons. Store in air-tight hardwood barrels. Test the strength of the solution with a Baume hydrometer and dilute for use according to the following table (see also p. 1029):

Dilutions For Dormant And Summer Spraying With Lime-Sulfur Mixtures

Reading on hydrometer

Amount of dilution.

Number of gallons of water to one gallon of lime-sulfur solution.

For San Jose scale

For blister mite

For summer spraying of apples

Degrees Baume

35.......................

9

12 1/2

45

34.......................

8 3/4

12

43 1/4

33.......................

8 1/4

11 1/2

41 1/2

32.......................

8

11

40

31.......................

7 1/2

10 1/2

37 3/4

30.......................

7 1/4

10

36 1/4

29.......................

6 3/4

9 1/2

34 1/4

28.......................

6 1/2

9

32 3/4

27.......................

6

8 1/2

31

26.......................

5 3/4

8

29 1/2

25.......................

5 1/4

7 1/2

27 3/4

24.......................

5

7

26

23.......................

4 1/2

6 1/2

24 1/4

22.......................

4 1/4

6

22 3/4

21.......................

3 3/4

5 1/2

21 1/4

20.......................

3 1/2

5

19 3/4

19.......................

3 1/4

4 3/4

18 1/4

18.......................

3

4 1/4

17

17.......................

2 3/4

4

16

16.......................

2 1/2

3 3/4

15

15.......................

2 1/4

3 1/2

14

14.......................

2

3

12 3/4