282 THE MONTHLY BULLETIN. 



THE COMMON NEMATODE OR POTATO EELWORM. 



Ileterodera radicicola Greef. 

 (Pigs. 284, 285.) 



Eelworms belong to a phylum of animals far below insects and are 

 never considered in a general work on entomology, but due to the seri- 

 ousness as well as the wide distribution of this worm as a pest of crops, 

 a brief account of it is herein included. 



General Appearance. — The presence of this pest is told by such 

 characteristic injuries as root knot on nursery trees, galls on tomato 

 vines and the rough warty surface of potato tubers. The animal 

 causing the injuries is commonly known as the nematode worm and was 

 recently given much prominence as the potato eelworm. The males and 

 young, the usual forms of the animal, are microscopic, transparent and 

 shaped much like minute eels. The female is pear-shaped and pearly- 

 white. The eggs are oval in shape and laid in great numbers. 



Life History. — The young eelworms feed upon the roots of various 

 plants causing galls or knots which may greatly impair growth. The 

 female develops within the affected areas and begins egg-laying, the 

 young hatching in a very short time afterwards. The winter is passed in 

 the original ho.st if it remains growing in the soil, such as nursery stock, 

 but if the host is removed they feed upon various plants left in the 

 fields. The young have the ability to encyst themselves so as to resist 

 great extremes of weather and unfavorable conditions, so once in the 

 soil it is very difficult to eradicate them. 



Distribution. — As a producer of root knot this animal is very com- 

 mon throughout the state, but somewhat more abundant in the central 

 and southern parts. As a potato pest it has been discovered only in 

 Los Angeles, Nevada, Monterey and Inyo counties. 



Food Plants. — According to Dr. E. A. Bessey there are four hundred 

 and eighty species and subspecies of plants affected by root-knot. The 

 list includes members of practically every flowering plant. Most of 

 the garden plants are affected, as are many of the field crops and fruit 

 trees. For definite information concerning the host plants the reader 

 is referred to pp. 10-22, Bulletin 217, Bureau of Plant Industry, U. S. 

 Dept. of Agriculture, by Dr. Bessey. 



Control. — The control of this pest is extremely difficult and eradica- 

 tion almost impossible. In greenhouses the soil may be sterilized with 

 steam or formaldehyde (one part to one hundred parts of water). 

 Rotation of crops which are not attacked by the nematode is perhaps the 

 best control measure in the field. Summer fallow, frequently turning 



