92 



CONTROLLING INSECTS AND DISEASES 



arsenate of lead for ordinary spraying is two pounds to fifty gallons 

 of water, though as much as four pounds is sometimes used. 

 Although it is usually assumed that arsenate of lead is perfectly 

 safe to apply to foliage without the addition of lime, slaked lime 

 is sometimes added in quantity equal to the arsenate of lead as a 

 precautionary measure when tender foliage is to be sprayed. 



White hellebore may be dusted on the plants in the dry form 

 without dilution; or it may be mixed with water at the rate of 

 one pound to fifty gallons, and applied as a spray. 



Nicotine sulfate is offered on the market in various degrees of 

 concentration and under various trade names. One of the most con- 

 centrated forms is known as " Black 

 Leaf 40. '^ This will kill plant lice even 

 when used as dilute as one part in a 

 thousand of water. 



GENERAL PRINCIPLES OF SPRAYING 



Suit the Material to the Plants. — 



In all spraying operations, the material 

 used must be of such a nature and ap- 

 plied at such a strength and in such a 

 manner that it will control the enemy 

 without injuring the host plant. Since 

 both enemy and host consist of organic 

 tissue, and both enemies and hosts vary 

 in their degree of resistance to spray 

 materials, the margin of safety is some- 

 times small. For this reason a material 

 which may be effective in controlling a 

 certain enemy on a given plant may be 

 unsafe to use in controlling a similar enemy on another kind of 

 plant. The usual strength of Bordeaux mixture is perfectly safe 

 for spraying potatoes, but is likely to injure melon foliage; hence 

 half strength Bordeaux mixture is used in the spraying of melons. 

 Methods of Applying Spray Materials. — Spray materials should 

 be applied as uniformly as possible to all parts of the plant to be 

 protected. If plant lice are working on the under surfaces of the 

 leaves, these parts must receive special attention. In order that 

 the apphcation may be uniform, the spray must be fine. The 

 fineness of the spray is determined mainly by two factors, the 

 character of the nozzle and the amount of pressure. A nozzle 



Fig. 50. — Compressed air knap 

 sack sprayer. 



