CONTROL OF ROOT-KNOT. 49 



expensive for ordinary use in larg^e fields where the crop value per 

 given area is far lower. The methods to be applied differ according 

 to whether the land is used for annual or short-lived crops or is pos- 

 sessed by a long-lived crop, such, for example, as fruit trees. In the 

 former case the treatment can be begim after the crop is off, while in 

 the latter it must be of such a nature that the trees present do not 

 receive injury. The latter problem will be discussed first. 



In the South the trees most generally affected seriously are the 

 peach, fig, mulberry, and walnut, wliile in California and Arizona 

 the Old World grapevine is seriously affected in addition. Many 

 other plants are subject to great injury elsewhere, such as coffee in 

 Biazil, Mexico, and the East Indies; papaya (Carica jyapaya) in 

 Florida and the Tropics; shmbs like tea in Ceylon and India, etc. 

 By consulting the list of plants subject to the disease it will be seen 

 that many are woody plants and that of these a number besides those 

 mentioned are seriously injured by the disease. 



CHEMICALS. 



Of the various treatments proposed, the use of chemicals has offered 

 a wide field for investigation and one that is by no means thoroughly 

 explored as yet. The more promising chemicals tested by the writer 

 are mentioned in the following paragraphs : 



Carbon Usulphid. — Tliis has been used in Europe for the phyl- 

 loxera on vine roots where the plants were dormant, without serious 

 injury to the vine. The writer's experiments, however, lead him to 

 look upon it with suspicion. Many plants were very quickly killed 

 by it and others seriously injured. Its use should not be attempted 

 without first testing its effect upon one or two trees. These should 

 preferably be dormant, at least not in an actively growing condition. 

 The root hairs are killed outright, so the plant must not be where 

 it will actively transpire until new root hairs are formed. The usual 

 method of procedure is to make holes in the ground to a depth of 

 several inches or a foot or more, the carbon bisulphid being poured 

 or injected into these holes and the latter covered up with dirt before 

 the liquid volatilizes. The fumes penetrate the soil and destroy 

 nearly all Yi\\ng things. Extreme care must be used in handhng 

 this chemical, as its fumes are poisonous and exceedingly inflammable, 

 being explosive when enough air is mixed with them. 



Carbon bisulphid will doubtless be of value in an orchard or grove 

 where it is desired to replace certain trees or fill vacant i)laces with 

 new plants. By its use the spots where the old trees stood or where 

 vacant places are to be filled can be thoroughly disinfected. After 

 a week or two the trees can be set out and, the soil being free from 

 nematodes, can make quite a start before the nematodes from the 



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