44 



MEANS OF CONTROLLING INSECTS 



came into use Paris green poison, which was des- 

 tined to revolutionize insecticidal methods. In 

 1872, it was suggested that a Paris green spray be 

 applied on cotton plants for the cotton worm and 

 on apple trees to kill canker-worms. Six years 

 later it was found that the poison spray effectively 

 checked the codling-moth, and this gave a new- 

 impetus to the warfare against insects, which has 

 finally resulted in the modern formidable array of 

 insecticide materials and elaborate machinery for 

 their application. 



The materials used as insecticides may be divided 

 into three groups, based largely on the two differ- 

 ent ways in which insects eat. Some insects, as 

 caterpillars, potato-beetles, and many others, have 

 their mouth-parts provided with strong jaws which 

 enable them to bite off and swallow solid particles 

 of their food-plants. (Figs. 53, 65.) Many other 

 insects, of which the plant-lice, stink-bugs, scale- 

 insects and mosquitos are familiar examples, have 

 their mouth-parts drawn out into fine threads which 

 are forced into the plant-tissues along a stiff, sup- 

 porting beak ; such sucking insects are unable to 

 eat solid particles and hence cannot be fed a poison 

 sprayed on the surface, for £hey can suck only liquid 

 food from the inner tissues of the plant-host. (Pigs. 

 54, 66.) To kill biting or chewing insects, it is 

 necessary only to apply a poison on the surface of 

 the plant where they are going to feed. But each 

 individual sucking Insect and not a certain part of 

 the plant must be hit with some material that will 

 soak into its body and kill, or that may smother by 

 covering the breathing holes along the sides of the 

 body. The third method is fumigation. 



Biting insects. — The insecticides used for killing 

 biting insects consist mostly of poisons which 

 have for their basis white arsenic. This substance 

 can not be used alone, as it dissolves slowly, and 

 this causes it to burn foliage severely. But it can 

 be combined with salsoda and lime to form a cheap 

 and effective poison spray. Boil 1 pound of arsenic 

 and 2 pounds of salsoda in 4 quarts of water until 

 dissolved ; then slake 2 pounds of stone lime with 

 this solution, and add 2 gallons of water. Use about 

 IJ quarts of this stock mixture in 40 gallons of 



67. Two-hoise spray machine for grapes. 



water or Bordeaux mixture, for general orchard 

 spraying ; for potato-beetles, double the dose of 

 poison. 



More than 2,000 tons of Paris green are now 

 used annually in America against insect pests. 



It is the standard poison spray, and is used at the 

 rate of 1 pound in 100 gallons on orchards, except 

 plum and peach, where only about half this 

 amount is safe ; on potatoes it is used at least 

 twice as strong. 



The arsenite of copper or green arsenite is simi- 

 lar to Paris green. 



Fig. I 



i. Spraying outfit that will give good service in 

 an apple orchard of forty to sixty acres. 



The arsenate of lead, which was first used against 

 the gypsy-moth in 1892, is coming into general use. 

 It adheres better to the foliage and can be used 

 very strong with safety, thus making it especially 

 useful against certain insects like the elm leaf -beetle, 

 codling-moth, plum curculio, rose-chafer, and grape 

 root-worm. It is sold in a paste form, one pound 

 of which contains only about half as much arsenic 

 as Paris green, thus necessitating using twice as 

 much of the arsenate of lead, or 2 to 4 pounds per 

 100 gallons for apple orchards and 4 pounds per 

 50 gallons in vineyards for grape root-worms. 



Hellebore is still much used for currant-worms, 

 but has been largely replaced by the Paris green 

 spray. 



Sucking insects. — The insecticides used for kill- 

 ing sucking insects are largely powders, oils or 

 soaps, which kill by contact or when they hit the 

 body of the insect. 



Pyrethrum powder is often used for house-flies, 

 but it is too expensive for general use in spraying. 



Tobacco in various forms is largely used for 

 fighting plant-lice in greenhouses, and sometimes 

 as a spray outdoors or in "washes" or "dips" for 

 domestic animals. Tobacco stems may be burned 

 slowly, creating a killing smoke, or tobacco dust 

 may be freely scattered over the plant, or decoctions 

 and extracts may be sprayed on the plants. 



Whale-oil and fish-oil soaps and various common 

 soaps are effective insecticides for plant-lice, scale 

 insects and many other sucking insects. Two pounds 

 'of soap dissolved in one gallon of water is the neces- 

 sary strength for killing scale insects on dormant 

 plants in winter, and one pound in four to six gal- 

 lons will kill plant-lice and recently hatched scale 

 insects. 



Kerosene and crude petroleum are among the 

 most effective materials for killing sucking insects. 

 Sometimes they can be applied in a fine spray on 

 dormant trees with little or no injury, but usually 

 it is necessary to combine them with soap in an 



