6s 



There are many solutions capable of killing a certain percentage 

 of adult worms and that can be applied to the soil before or after 

 planting, but the strength and the amount of the solution necessary 

 to kill nematodes in the soil is considerably greater than that neces- 

 sary when the worms are isolated. This is clue to the difficulty of 

 bringing the solution into contact with each particle of matter in and 

 around which the nematode thrives. 



The most effectual, complete, and practical method at the pres- 

 ent time of exterminating nematodes in greenhouses is by heat- 

 ing the soil by means of steam. This can be accomplished with- 

 out much expense providing proper attention is paid to the meth- 

 ods of applying the steam. 



A pressure of steam exceeding 50 lbs. is not only cheaper, but 

 more effective than a pressure which falls below this, and the 

 amount and cross section area of the tile is important. See p. 53. 



The cost of heating soil depends upon the equipment employed 

 and cost of labor, etc. Probably not far from 100 cu. ft. of soil 

 under the most favorable conditions can be heated in one hour's 

 time to a temperature of over 200° F. 



The minimum amount of heat necessary to kill nematodes and 

 their eggs while confined to the soil is about 140° F., but for all 

 practical purposes it is desirable to make use of a higher tempera- 

 ture, at least from 180^-212° F. 



The benefit of steaming or sterilizing the soil is not alone confined 

 to the destruction of nematodes. Many other greenhouse pests are 

 killed. The mechanical conditions of the soil are moreover greatly 

 improved ; the humus compounds are rendered more available for 

 plant food, which results in giving plants grown in sterilized soil a 

 considerable acceleration in their rate of growth. 



The changes of the environment which appear to affect Heterodera 

 the most are freezing and desiccation. Either of these agencies 

 might be employed in certain cases to kill nematodes. The latter 

 gives promise of becoming a cheap and efficient method. 



