50 DISEASES OF FIELD & GARDEN CROPS. [CH. ix. 



This is said to prevent the attacks of the onion-fly, for it 

 is believed that the flies select the younger onions for the 

 deposition of their eggs in preference to those of more 

 mature growth. 



Where possible all mildewed material should be burnt, 

 for no fact is better known than that mycelium or fungus 

 spawn is often perennial. 



Like many other plant ailments, the diseases of onions 

 require investigation. Several forms of disease are known 

 to growers, of which no explanation has at present been 

 forthcoming. In one form the whole crop turns sickly 

 yellow just before ripening, the tops soften, the bulb be- 

 comes detached, the roots decay, and the entire growth 

 soon becomes rotten. Another disease causes the onion 

 to become thick and soft-necked, the bulb in proportion 

 being small. Sometimes mildew attacks the full -sized 

 and apparently not thoroughly -ripened bulb after it is 

 harvested, and commences from the outside. 



