CHAPTER XVIII 



UNCLASSIFIED PESTS 



Some of the insects and insect-like animals are so miscel- 

 laneous in their feeding that they cannot be associated clearly 

 with any one crop. A few of these are treated together here. 

 Some of them are very troublesome and are difficult to combat. 



The Root-Knot Nematode 



Heterodera radicicola Greef 



A great variety of plants is subject to serious injury from 

 the attacks of minute nearly transparent worms that bore into 

 the roots, causing gall-like knots or outgrowths to develop. 

 In England these are known as eel-worms.* The swellings on 

 the roots are produced by the plant in its attempt to repair 

 the injury caused by the presence of the w^orm. The normal 

 growth of the root tissue is disturbed, with the result that the 

 sap-tubes are distorted and unable to carry their load of raw 

 plant-food up to the leaves. Badly infested plants take on a 

 weak, unhealthy appearance, become stunted and sometimes 

 die. 



The root-knot disease is prevalent throughout the tropics, 

 sub-tropics and the warmer parts of the temperate zone. In 

 the United States it is occasionally found as far north as New 

 York, Michigan and Nebraska but is of little importance except 

 in the southern states and in central and southern California. 



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