VEGETABLE DISEASES, 195 



Onion Mildew (Peronospora schleideiii). — A fungus 

 which frequently does serious injury to the onion crop. 

 It occuiTS in the form of a mould on the leaves. At first 

 its presence may be detected by yellowish patches, fol- 

 lowed later by a white, and then a greyish-lilac mould. 

 The disease causes the leaves to shrivel and the growth 

 of the bulb to be stunted. 



Bemedies. — Mix two parts of slaked lime with one of 

 sulphur, and dust the plants early in the morning whilst 

 the dew is on the foliage. Spraying the foliage with a 

 solution of sulphide of potassium and water (Formula 23) 

 is another good remedy. All diseased plants should be 

 promptly burnt, and onions not be grown on the same 

 land for three years. 



Onion Rust (Puccinia porri). — This fungus attacks 

 both onions and chives. It forms reddish-brown pustules 

 on the leaves, and often destroys the w^hole crop. 



Eemedt. — The only course to pursue is to burn all in- 

 fected foliage. 



Onion Scab (Vermicularia circinians). — Fortunately 

 not a very common disease. It appears in the form of 

 small black velvety tufts, disposed in concentric circles 

 on the outer scales of the bulbs. These black patches 

 disfigure the bulbs, and practically render them unusable. 

 Generally speaking, the disease manifests itself most on 

 fully-grown bulbs. 



Kbmedies. — When storing the bulbs reject every one pos- 

 sessing the faintest tinge of the Scab, otherwise the fun- 

 gus will infect the healthy bulbs and spoil them. Dis- 

 eased bulbs should not be left on the ground, but be 

 promptly burnt. 



Onion Scierotinia (Sclerotinia bulborum). — A fun- 

 goid disease appearing in early summer in the form of 

 yellow blotches on the leaves, followed by an olive-brown 

 mould. The mycelium of the fungus eventually descends 



o 2 



