3o8 Diseases of Truck Crops 



germination. Poor sprouting may sometimes be 

 attributed to shipping of seed in overheated cars. 

 In this case the seed when cut open will be seen to be 

 blackened at the heart, a trouble soon to be con- 

 sidered. 



Leaf Roll 

 Cause Unknown. 



Leaf roU is but an old disease with a new name. 

 The trouble has been carefully studied by Orton. ^ 



Symptoms. As the name indicates, the charac- 

 teristic symptom is a rolling of the leaves (fig. 58 a). 

 The leaflets roll and curl upward on their midrib, 

 often assuming a tube shape. This condition may 

 involve the upper leaves of a plant or in serious cases 

 the entire foliage. Rolled leaflets assume a sickly 

 yellow reddish to purplish color. This is especially 

 apparent on affected plants grown from tubers of a 

 previously infected crop. 



The effect of leaf roll is to interfere with proper 

 growth. This generally results in a premature dying 

 of the leaves. The effect of the disease on the tubers 

 seems to be strongly marked. The tubers in the hill 

 are small, unfit for market and the jrield is often re- 

 duced by about one half. The disease is not con- 

 tagious in the sense that it can spread from plant to 

 plant; but the inherent weakness is transmitted to 

 the seed. This when sown again will show new out- 

 breaks of leaf roll the following year. True leaf roll 



' Orton, W. A., U. S. Dept. of Agr. Bui. 64 : 1-48, 1914. 



