1 62 Diseases of Truck Crops 



between two leaves, are the first symptoms on the 

 plant. The disease seldom blackens the full length 

 of the stem. The part below the black spot remains 

 healthy, while the part above wilts and dies, since 

 the infected area prevents the upward flow of water 

 and plant food to the part beyond the killed area. 

 Stem infection does not always indicate underground 

 infection. Often where the vines are affected, the 

 roots, when pulled out, seem to be free from black 

 rot. In case of underground infection, sometimes 

 every root in the hiU is black rotted and there may 

 not be the least indication of the disease on the stem 

 of the plant. At digging time, roots which show the 

 disease are somewhat paler in color than the healthy 

 ones of the same variety, a s3miptom which seems to 

 be general in some soils and not in others. When 

 roots are infected with black rot, the edible qualities 

 are poor because of the bitter taste. This becomes 

 more marked the longer the roots are kept in storage. 

 Although the black rot spot is only superficial, the 

 bitter taste in cooking is imparted to the entire root, 

 showing that it is soluble and easily diffused into 

 adjacent tissue. 



Introduction and Spread of Black Rot. In the seed 

 bed, the trouble begins with diseased seed. Even 

 though the greatest care is exercised in discarding 

 the seed, some infected roots wiU find their way into 

 the bed. Not all growers are careful in their selec- 

 tion of seed, and often through lack of knowledge of 

 the malady, diseased roots are used in bedding, or are 

 discarded and thrown out near the bed. These seeds 



