16 farmers' bulletin 199. 



common pests in gardens and lawns may be destroyed by the method 

 recommended for use against ants infesting the soil. For best re- 

 sults the soil should be fairly permeable and at least 8 inches in 

 depth. 



TREATMENT FOR APHIDS LIVING UNDERGROUND. 



The first extensive use of carbon disulphid as an insecticide was 

 against the grape Phylloxera in France. The Phylloxera is a species 

 of aphis which lives upon the roots of the vine. It is native to 

 America but was introduced by accident into France about 1859, 

 where for a time it threatened to destroy the grape-growing industry. 

 By 1863 more than 200,000 acres of vines were being treated annually 

 with carbon disulphid for this pest. The following paragraphs give 

 a brief summary of the principal conclusions reached by French 

 workers in their fight against the Phylloxera. They are included 

 here because they have a general application to all fumigation for 

 underground insects. 



DIFFUSION OF THE VAPOR IN THE SOIL. 



The liquid evaporates in the soil as it does in the air, only much 

 more slowly. The vapor diffuses through the air spaces of the soil, 

 producing an atmosphere that may be fatal to all insects reached 

 by it. The rate of evaporation, extent of diffusion, and persistence 

 of the vapor in the soil vary widely in soils of varying character and 

 condition. It becomes necessary, therefore, to vary the rules for 

 application according to the influence of these factors to secure the 

 destruction of all insects without injury to the plants. 



EFFECT OF SOIL MOISTURE. 



Carbon disulphid evaporates most rapidly in a warm, dry, sandy 

 soil, and the persistence of the "vapor is shortest in such soil. In 

 fact, in such soil the diffusion is so rapid that most insects will sur- 

 vive an ordinary treatment, and if the dose is increased greatly to 

 kill the insects there is grave danger of killing the plants also. 

 Treatment can not be applied successfully in such soil unless the 

 surface soil can be wet or covered after the treatment. On the other 

 hand, diffusion is slowest in very heavy, wet, clay soils, and when 

 the soil is saturated with water the evaporation is almost entirely 

 prevented. Moisture lowers the temperature and decreases the per- 

 meability of the soil ; it also prevents evaporation and retards diffu- 

 sion. Between these two extremes there is a medium character and 

 condition of the soil which is most favorable for the treatment. 



