DISEASES OF CROPS 961 



SWEET POTATO 



Soft Rot (Rhitopus nigricans, Ehrbg.). — This storage rot is caused by 

 the bread mould fungus and can be readily recognized. It is accompanied 

 by a sweetish odor and dense growth of white mould which becomes black. 

 It spreads rapidly, but can be controlled by proper ventilation and regula- 

 tion of temperature. 



Black Rot (Sphceronema fimbria! um [Ell. and Halst.], Sacc). — This 

 disease occurs in both field and storage house. It appears as dark-brown 

 or black, irregular, dry patches on the potatoes, sometimes causing break- 

 ing or cracking near the center of the diseased area. On the young sprouts 

 and stems it causes black patches and frequently kills the entire plant. 



Treatment. — Do not use diseased plants for setting. Do not use 

 stable manure. Grow seeds from slips. These slips should be cut from the 

 old plants and set as early in July as possible. 



Stem Rot (Nectria ipomoece, Halst.). — This disease attacks the stem 

 near the surface of the ground and spreads in both directions, frequently 

 causing the death of the plant. The interior of the stem shows a yellow 

 discoloration. 



Treatment. — Rotate the crops and use slip seed. 



Note. — There are a number of other rots and diseases which will not 

 be taken up in this discussion. 



PEANUT 

 Peanuts are subject to several foliage and root diseases of more or 

 less importance. Growers of this crop should consult with their state 

 agricultural experiment station. 



TOBACCO 



Granville Tobacco Wilt (B. solenacerarum, Smith). — This is due to the 

 same organism as the wilt of the potato, tomato, peppers and eggplants. 

 (See Potato.) 



Mosaic, Calico or Mottle Top. — The cause of this disease is still some- 

 what uncertain. The leaves of the diseased plants show dark and light 

 areas and frequently irregular thickenings or twistings. 



Treatment. — Remove the diseased plants. Be careful not to touch 

 healthy plants while working with the diseased plants. The disease can 

 be communicated by contact. 



Leaf Spots. — There are a number of leaf spot diseases and also mildews 

 which cause more or less trouble. 



Root Rots (Thielavia basicola, Zopf.). — This disease is a rotting of 

 the roots, accompanied by the production of numerous new roots. The 

 affected plants are dwarfed and frequently killed. 



Treatment. — Sterilize seed-bed. Rotate crops. Avoid liming and 

 acid fertilizers. 



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