1920.] The White Rot Disease of Onion Bulbs. 1099 



Methods of Contror. — The only means at present known of 

 exterminating White Rot, once it becomes established in any 

 part of a garden or field, is by starving out the fungus from the 

 soil. This can only be effected by keeping the ground free 

 from onions and aUied crops f6r a number of years. The exact 

 length of time that is necessary cannot be stated, but j udging 

 by analogy eight or even ten years may not be too long. During 

 this period the soil should be " worked " as much as possible, 

 although the utmost care should be taken that contaminated 

 soil is not conveyed to clean land. It would be advisable to 

 make any new onion beds at a considerable distance from the 

 infested land. 



When once the bulbs become attacked practically nothing 

 can be done to save them; the disease will gradually work 

 through and destroy the whole bulb. As a general rule and 

 when practicable the diseased plants should be removed as 

 early as possible before the formation of sclerotia takes place. 

 The plants should be carefully dug up, removed from the 

 ground and burned. If this is persisted in during the entire 

 season further infestation of the soil by sclerotia will be 

 prevented. 



In the case of small beds in private gardens and allotments 

 when large bulbs are affected and the attack appears to be 

 general it may even pay to lift the entire crop at once before 

 the whole bed becomes infected. The healthy bulbs, being 

 immature, should not be stored but put aside for immediate 

 consumption ; the diseased bulbs (or at any rate the diseased 

 portions of them) should be burned at once. 



Up to the present no success has been obtained with the 

 use of soil fungicides, the hard coat of the sclerotia being 

 probably as resistant to chemicals as the spores of the Potato 

 Wart Disease. 



No varieties of onions can be recommended at present as 

 immune. Shallots are usually resistant, and leeks are not 

 commonly affected. These crops might, therefore, in pressing 

 cases be grown on infested land, but it would be preferable 

 not to do so. 



White Rot is not a disease which is Hable to be introduced 

 with the seed. 



