PART IX. PESTS AND DISEASES 

 OF PLANTS 



SPRAYS AND POISONS FOR INSECTS * 



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 exceedingly difficult task 

 to select a preparation or formula which will give the best results for 

 the outlay of money. It is the desire of the writer to give 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 insects which are capable of taking the poison internally. 

 They are the cheapest and therefore used wherever practical. The 

 contact sprays are for piercing and sucking insects as well as biting 

 and chewing insects which can not be controlled by arsenicals. The 

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

 directly and the repellents, being distasteful, prevent or repel attacks. 



Arsenical Insecticides. 



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. 



"This information is compiled from the latest writings of E. O. Essig, instructor 

 in entomology of the University of California. 



