8 



NEMATODE GALLWORM ON POTATOES, ETC., IN NEVADA. 



clean and healthy seed from fields where a critical inspection shows 

 that the disease has not been present. 



All culled potatoes from the field should be examined, for even 

 when disease is present the bulk of the crop may be unaffected. 

 The gallworm does not occur in the potato-gro^^^ng districts of the 

 Northern States, particularly North Dakota, Minnesota, Wiscon- 

 sin, and Maine. Seed obtained originally from these States and 

 grown on fields that are free from the gallworm should be safe to 

 use in planting other uninfested fields. Too much stress can not 

 be laid upon the importance of securing for ])lanting 

 potatoes which are uninfected and in planting them 

 on uninfested land. 



LOCALIZATION OF INFESTED AREAS. 



The practical ])roblem which confronts the potato 

 growers of Nevada is the location of all fields which are 

 mfested with tliis parasitic nematode. The present 

 indications are that the nematode infestation is by no 

 means general in irrigated land. The nematode has 

 probably existed in some of the older irrigated lands 

 of the State for many years, but there is much new 

 land being put under irrigation in Nevatla, which it 

 seems probable is entirely free from this worm. If all 

 of the infested areas can be located by a critical inspec- 

 tion, it will be possible to produce potatoes in large 

 quantities on uninfested land and devote the infested 

 land to crops which are resistant to the parasite. 

 There are probably some fields in the State which 

 have been devoted to potatoes during the last year or two on which 

 the parasite does not occur, and from these uninfested fields seed might 

 be secured. It would be much safer, however, to obtain seed from 

 the Northern States, such as Minnesota, Wisconsin, or North Dakota, 

 with which to plant new land, rather than to risk the infestation of 

 the new land with local seed. But it will be impossible to proceed 

 intelligently in combating the ravages of the gaUworm until the 

 infested areas have been located, so that the danger of infestation, not 

 only by means of potatoes but in many other ways, can be fully 

 ascertained. 



SUSCEPTIBILITY OF OTHER PLANTS. 



In view of the fact that the gallworm is parasitic on many plants 

 other than potatoes, it is important not to foster the ])a]asite by the 

 culture of plants which are subject to its attacks. The following is 

 a list of some of the plants which are readily and seriously attacked 

 by the gallworm and which should never be grown on infested fields 



ICir. 91] 



:ioo 



Fig. 5.— Newly de- 

 posited egg of the 

 gallworm. These 

 eggs are distinctive 

 featiues of the nem- 

 atode disease. They 

 occur in large num- 

 bers, as shown in 

 figure 4. (After N. 

 A. Cobb.) 



