December, '19] SMITH: NEMATODE DISEASE OF RED CLOVER 461 



an article concerning the discovery of this pest in the Northwest and 

 the article was distributed through the Office of Information of the 

 United States Department of Agriculture. A reference to the disease 

 of red clover was made in 1918 by Mr. A. C. Burrill who suggested 

 that the trouble might be due to the attack of certain mites and the 

 larvae of the fungus gnat, Sciara trifolii Pett.^ 



Red clover seems to be the only plant that is seriously affected in 

 the Northwest although occasional instances have been observed where 

 alsike and white clovers were injured. This limited range of host 

 plants may possibly be explained by the statement of certain European 

 writers that there are different "biological strains" of T. dipsaci, each 

 strain being specialized in its feeding habits to one host plant or to a 

 few closely related host plants, so that it is unable to readily attack 

 other species of the large number of plants that are listed as hosts of 

 this nematode. It remains to be seen if the T. dipsaci that is causing 

 such severe damage to clover in the Northwest will eventually become 

 a pest of the numerous crops which the species is said to attack in 

 Europe and other foreign countries. 



The nematodes appear to enter the clover plants at the surface of 

 the ground, first working into the stipules of the leaves which surround 

 the developing stems and later entering the stems. The infested parts 

 near the ground become enlarged, spongy, and finally turn brown and 

 rot off. The worms also occur higher up in the stems, and in the leaves 

 and branches where they cause distortions and enlargements. The 

 malforming of plants is most pronounced in autumn and early winter. 

 During the summer the foliage of affected plants usually has an un- 

 healthy, striped-yellow appearance and the plants as a whole are more 

 or less stunted. 



The death of diseased plants is hastened in the greater number of 

 cases by the work of secondary agents, the most important of which 

 seem to be the root mite, Rhizoglyphus rhizophagus Banks, the larvie of 

 the mycetophilid, Sciara trifolii Pett., and the larvae of Sitones hispid- 

 ulus Germ., a snout beetle that is common in clover fields in the North- 

 west. The greater injury results to clover fields the second j'car or 

 longer after seeding when both the nematodes and the insects are 

 found to be more abundant. Several fields have been observed, 

 however, whicli had to l)e plowed up the first year after seeding. 



Considerable work on the control of this nematode has been carried 

 on in Europe and such measures as traji phints, rotations witli imnuine 

 crops, (k^ep plowing, fallowing, application of various chemicals to tiie 

 soil, and intensified cultivation have been recommended. It has been 

 found that the larvir of the worms ran remain dried up for a p(>rio(l of 

 two anil one-half years without loosing their viability. This, along 



