144 INSECT PESTS 



Onion Fungus {Peronospora schUideni) is common in 

 many districts. It takes the form of a lilac-coloured 

 bloom on the foliage of the plant, and if attacked young 

 the bulb is ruined. A sketch is shown of the appearance 

 of the parasite under the microscope. Dusting with 

 Ume and sulphur is the best measure against Onion 

 Fungus. (See Plate 33.) 



Cabbages sometimes get badly deformed with White 

 Rust on the underside of the leaves. This destructive 

 fungus, Cystopus candidus, is common aU over the world. 

 It is really a parasite of Shepherd's Purse, on the leaves 

 of which the clusters of spore-bearers may be seen. 

 Where the fungus attacks the stalks of both wild and 

 cultivated plant an ugly malformation takes place, which 

 is a hotbed of disease for the next generation of cabbages. 

 Such distorted leaves should therefore be systematically 

 burned and weeds like Shepherd's Purse eradicated. This 

 fungus thrives, like most of its kind, in damp situations, 

 and cabbages planted in a fairly dry, open place are most 

 likely to escape injury. (See Plate 33.) 



A few examples of fruit fungi will perhaps be found of 

 value. Among these the outstanding example is the 

 American Gooseberry Mildew [Sphceritheca mors-uvce), 

 which in late years has devastated bush fruit in this 

 country to such an extent that it is the subject of several 

 Acts of ParHament, and figures as a notifiable disease 

 under penalties for non-compHance. (See Plate 35.) 



American Mildew presents two well-marked forms, the 

 white or summer, and the brown or winter stage. In 

 both cases there is spore-production. The summer 

 spores are, however, dehcate, and a spell of dry weather 

 does as much as anything else to check their increase. 

 It is the winter, or resting-spore, which is the real menace, 

 as it can remain either on the bushes, immune from frost, 

 or in the soil, perhaps for a year or so, and still germinate. 



The greatest precautions must be taken by fruit- 

 growers wherever this disease occurs, as the spores may 



