INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 463 



SPRAYS AND POISONS 



Spraying for insect pests has become a very important factor in 

 the growing of a large number of crops and especially in horticultural 

 work. As such it is now a regular and well established business 

 which has received a very large amount of investigational work-, 

 with the result that there are today efficient sprays for most of the 

 important ailments a tree or plant is heir to. This is true of both 

 the home-made and commercial products, and it is often an exceed- 

 ingly difficult task for the orchardist and farmer to select a prepara- 

 tion or formula which will give the best results for the outlay of money. 



It is beyond the limits of any ordinary work to give a complete 

 list of the formulae and uses of all the preparations which may be 

 designated as home-made products, and it is none the less prohibitory 

 to give a list of all the commercial insecticides now upon the market. 

 However, it is the desire of the writer to idve the formulae and 

 methods of preparation of some of the most important which can be 

 made at home or the equivalents of which may be obtained from 

 commercial manufacturers. 



In general insecticides, whether they be liquids, solids or gases, 

 are usually listed in three main classes, viz: arsenical, contact and 

 repellent, The arsenical sprays are used in controlling biting and 

 chewing insecls which are capable of taking the poison internally. 

 They are the cheapest and therefore used wherever practical. The con- 

 tact sprays are for piercing and sucking as well as biting and chewing 

 insects which can not be controlled by arsenicals. The gases and repel- 

 lents are used for all classes of insects; the gases kill directly and the 

 repellents, being distasteful, prevent or repel attacks. 



ARSENICAL INSECTICIDES FOR BITING AND 

 CHEWING INSECTS 



Paris green and London purple were the first arsenicals used as 

 insecticides, but of late years it has been discovered that lead arsenate 

 and zinc arsenite, while not quite as strong, are much less liable to 

 damage the fruit and foliage and have therefore largely replaced 

 the stronger arsenicals. Paris green, however, is still used for certain 

 insects, and where there is no danger to foliage as in the use of baits, 

 it is used very largely. White arsenic is also used for this purpose 

 and is much less expensive. 



Arsenicals are largely used in combating such insects as grass- 

 hoppers, armyworms, cutworms, caterpillars, slugs, beetles, or any 

 others which. actually eat the foliage or fruit. 



LEAD ARSENATE 27 



A. Lead arsenate (paste) I to s pounds 



Water 1011 gallons 



B. Lead arsenate (powder) - t" 8 pounds 



Water 100 gallons 



327 There are two kinds of lead arsenate on the market — the ordinary, or acid, which 

 is generally used and at times causes severe burning to fruit and foliage it applied 

 too strong, and neutral lead arsenate, which is perfectly safe and should be used 

 wherever there is any danger of burning tender fruit and foliage, or usuallj In com- 

 bination when other insects or fungi are to be sprayed at the same time. 



