4 NEMATODE GALLWORM ON POTATOES, ETC., IN NEVADA. 



for the same nematode which has caused the potato disease in Nevada 

 is widely distributed throughout the United States and is causing 

 every year much more damage than is generally understood. 



It is the purpose of the present publication to give some information 

 concerning the parasite which is the cause of this potato disease, 

 briefly describe its life liistory, indicate some of the sources of infec- 

 tion and methods of transferring the parasite from one place to 

 another, and suggest remedial measures for combating the disease in 

 Nevada. 



It is of the utmost importance to those concerned to act intelli- 

 gently in dealing with the present situation in Nevada.' The potato 

 crop is one of tlie most profitable crops at present produced on the 

 irrigated lands of Nevada. When not injured by the gallworm the 

 potatoes are of very high quality and usually command a higher 

 price in California markets than potatoes from any other section. 

 It is important, therefore, to prevent the further spread of this 

 parasite in the potato-growing sections of the State and so to reduce 

 its numbers where it now occurs that it will cease to be a serious 

 pest. This can be accomplished through first locating all of the 

 infested fields and then devoting these fields to the production of 

 crops upon which the nematode can not live. This location of 

 infested areas will require very thorough inspection of all the fields 

 which have been used for potatoes within recent years. Such an 

 inspection to be thorough must be made by examining the roots of 

 plants that are susceptible to the attacks of this species of nematode. 

 The inspection should go still farther and include a critical examina- 

 tion of all fields on which it is proposed to plant potatoes. The 

 nematode gallworm is parasitic on so many plants that it may 

 easily live in the soil for many years if plants which it can attack 

 are present. 



A critical inspection of the irrigated lands of Nevada will probably 

 show that the nematode gallworm occurs only in small and restricted 

 areas. If these infested areas are definitely located and ]Mecautions 

 are taken to avoid carrying the worm to other fiekls where it does 

 not now occur, and if at the same time these infested fields are 

 devoted exclusively to crops which can not harbor the parasite, it 

 should be possible in a few ye are to reduce its numbers to a point 

 where it will cease to be a factor of importance. 



CAUSES OF THE POTATO DISEASE. 



The so-called eelworm or gallworm disease (also called "root- 

 knot") is caused by a minute nematode worm {Heterodera radicicola 

 (Greef.) Mtill.). Figures 1 and 2 show the two sexes of this worm 

 enlarged to illustrate various features which are so small as to be 



[Cir. 91] 



