MARKET DISEASES OF VEGETABLES. 43 



cicervuli but become covered with a black, velvety growth of 

 Alternaria species. 



PEPPER: RHIZOPUS ROT. 



(See Rhizopus Rot). 



PEPPER: SLIMY SOFT ROT; BACTERIAL ROT. 



(See Slimy Sjft Rot). 



PEPPER: WATERY SOFT ROT; SCLEROTINIA ROT. 



(See Watery Soft Rot). 



PEPPER: SUN-SCALD. 



(See Sun-Scald). 



POTATO: BLACK SCURF AND RUSSET SCAB. 



. Cause: A fungus (Rhizoctonia). 



Black scurf and russet scab are skin diseases. Affected 

 potatoes are rough and dirty in appearance, or may have a 

 cracked or corroded skin. Both are field diseases caused by 

 the same fungus. 



Black scurf is characterized by the presence of small 

 brown or black masses or sclerotia on the tuber, often re- 

 ferred to as "dirt which will not rub off." These masses 

 may be circular or irregular in outline and single or joined 

 into series. Washing the tuber brings these into sharp relief. 



Russet scab is a corrosion of the tuber skin. In some cases 

 smooth-skinned tubers show local or general netting, either 

 slight, or so extensive as to resemble the skin of netted varie- 

 ties. In advanced stages the corrosion becomes channeled, 

 and the intersecting channels may become so deep that the 

 tuber surface suggests alligator hide. 



In many cases, tubers are literally covered with black 

 scurf without any apparent russeting, while in other cases 

 the presence of the fungus seems to cause only a cracking 

 or scabbing, without any sclerotia. 



Generally neither black scurf nor russet scab are serious 

 enough to affect the market value of potatoes. The former 

 occasionally is severe enough to affect the appearance of the 

 tuber. At times, in very moist cars or storage places, the 

 sclerotia germinate, and the potatoes become covered with 

 a luxuriant growth of mold which detracts from the good 

 appearance of the lot. Russet scab, however, affects the 

 appearance of the tuber more markedly, and often corrodes 

 the skin suffciently to necessitate deep paring, which is 

 attended by a waste of food. 



Ref. (50); (64). 



POTATO: SILVER SCURF. 



Cause: A fungus (Spondylocladium atrovirens). 



