162 Diseases of Economic Plants 



conveyed by grafting, but otherwise develops only after the 

 sting of a leaf hopper (Eutettix tenella) that has been in con- 

 tact with beets affected with curly-top. Bacillus morulans 

 Bone, has been associated with curly-top, but its causal 

 relation not demonstrated. 



Root-rot ^^^ (Corticium vaguni). — Beets affected with 

 this rot usually show first attack at the bases of the outer 

 leaves, which turn black. The stalks weaken and allow 

 the leaves to fall prostrate, though they do not lose their 

 color at once. The disease thence passes into the crown, 

 turning the involved parts brown and later leading to crack- 

 ing of the root. In this condition the mycelium of the 

 fungus is clearly evident in the cracks. Eventually the 

 whole top may rot off. The spread is rapid from plant to 

 plant in the field. Dry or cold weather may so retard the 

 invasion that the plant can recover if not too badly affected. 



The disease is probably the same that has been destruc- 

 tive to sugar beets in Germany. It has been reported from 

 several places in the United States. 



Air-slaked lime, 60 to 70 bushels per acre, has been recom- 

 mended. 



Phoma Root-rot ^^^ (Phoma beta (Oud.) Frank.). — Upon 

 the roots a shrunken, coal-black discoloration, extending 

 sometimes quite to the center, indicates the presence of this 

 dry rot. No disagreeable odor attends the rot. Upon the 

 affected surface pycnidia appear as very minute pustules. 

 Upon the leaves this same fungus forms large, circular, 

 dead spots. The disease may also appear on seedlings, caus- 

 ing damping-off. 



All infected leaves should be removed from the roots 

 before placing in storage. 



Root-knot and Hairy-root (nematodes).-"^- ^^* — Two spe- 

 cies of nematodes affect beets, one of which produces root- 

 knot, the other hairy-root, both of which are quite destruc- 

 tive. Root-knot, due to nematode-infection, is discussed on 

 p. 24. Hairy-root shows first symptoms, as the hot season 

 begins, in a wilting, yellowing, and dying of the outer leaves, 



