40 DISEASES OF CROPS. 



been described. It destroys the foliage, and thereby 

 arrests the growth of the plant. 



Cure. — Mr. C. Whitehead, F.L.S., recommends washing 

 the leaves, by means of a garden engine, with a solution 

 of soft soap and quassia. 



The Carrion Beetle {Silpha opaca), already de- 

 scribed, injures mangel-wurzel as well as beetroot. 



The Club- Root of Mangel {Plasmodiophora bras- 

 sicce) is a fungoid growth which will be described later 

 on in this chapter (see "The Parasites of Turnips "). 



The Mangel-Leaf-Rust {Trichobasis betce) has 

 already been described among the diseases of beet-roots. 



(4) The Parasites of Onions {Allium cepa). 



The Onion Eelworms (Tylenchus allii), according 

 to Dr. Ritzema Bos, cause putrefaction to occur within 

 the bulbs. They are found in the parenchyma of the 

 bulbs and leaves. Much injury is done by these pests 

 to the onion crops of Holland. 



Prevention and Cure. — See " The Eelworms of Clover " 

 (chap. ii.). 



The Onion Fly {Anthomyia ceparum) belongs to 

 the same genus as the beet fly. The eggs are laid in 

 April or May, on the lower leaves of the young onion 

 plant or on the ground. After hatching, the larvae, which 

 are devoid of legs, and about three-eighths of an inch 

 long, feed inside the bulbs, having previously gnawed a 

 way into the interior. Here they reside from fourteen 

 to sixteen days, causing a considerable amount of 

 damage to the bulbs, which finally become rotten. After 

 the expiration of a fortnight's residence within the bulb, 

 they leave it and enter the ground, and there turn to the 

 pupal stage. If the grub turns to the pupal stage in the 



