316 PRINCIPLES OF SPRAYING 



Tobacco dust is used both as an insecticide and as a repellant. 

 Dusting this on plants to repel insects may drive them away 

 (Fig. 229), or the nicotine extracted by the moisture of the dew or 

 rain may kill some of the insects. Plant lice on the roots of apple 

 trees or other plants are often destroyed by the use of tobacco dust. 

 This is applied in the soil after digging away the earth from about 

 the roots. Extract of tobacco stems is used in much the same way. 



Lime-sulfur solution is one of the best insecticides for use against 

 San Jose" scale and other forms of scale insects. The coating formed 

 over the surface of the bark seems to smother the scale insects and 

 they are killed whenever the spraying is done thoroughly. 



Directions for making lime-sulfur solutions have already been 

 given in this chapter. This may be applied in either the winter or 

 the summer form according to the requirements; the strength is 

 varied to suit the season. 



Pyrethrum. — Persian insect powder is made from the heads of a 

 plant belonging to the genus Pyrethrum, which we frequently find 

 growing in gardens. It is a light brown powder which is somewhat 

 dangerous to use in houses. It can be used if care is exercised to 

 not breathe it. The powder loses its strength rapidly and must be 

 kept in a closed vessel, or used when freshly made. It is commonly 

 used in the powder form, but may also be dissolved in water at the 

 rate of one ounce to three gallons. In the dry form it may be mixed 

 with other powders such as lime dust, borax or flour. It may be 

 used for fumigation by putting the powder on a shovel of hot coals. 



Pyrethrum is sometimes dissolved in alcohol, one part to four 

 parts of alcohol by weight. Shake this in a bottle and allow to 

 stand for a week. This may be filtered through a cloth and used in 

 an atomizer for house plants. Some water may be added if too 

 strong for the plants. An extract of pyrethrum may be made 

 somewhat in the manner of tea by pouring boiling water over the 

 flower heads and allowing to stand for a few minutes. 



Principles of Fighting Sucking Insects.— Remember that the 

 spray materials must be strong enough to kill the insect by contact 

 and must be applied when the insects are present. Oils and dust 

 are both fairly good insecticides if they come in contact with the 

 insects. Do not expect the insects to be killed unless the insecticide 

 does the work when the insects are present. 



Future attacks of the insects are not affected by spraying or 

 dusting done in advance of an attack. Soft bodied insects are 

 much easier to kill by contact than are those of the scale group. 



