PERONOSPORA 109 



As a continuance of favourable weather cannot be depended 

 upon, it is imperative that spraying should promptly follow the 

 appearance of the disease. Bordeaux mixture may be used, half 

 strength, but lime water should be used in its preparation, other- 

 wise the leaves are apt to be scorched. Experiments conducted 

 by me at Kew proved that three per cent, of sulphate of iron 

 dissolved in water can be used for spraying onions without 

 injuring the leaves, and this preparation is quite as effective 

 against mildew as Bordeaux mixture, and is both cheaper 

 and more easily prepared. The sulphate of iron must be 

 pure. As resting-spores are usually produced in abundance 

 in the leaves, and as such leaves fall soon after infection, it is 

 certain that the land will be infected. In this case onions 

 should not be grown on the land for some years afterwards. 

 Good drainage is a check to disease. 



Shipley, A., Kew Bull. No. 19 (Oct. 1887). 

 Whetzel, H. H., Cornell Agric. Exp. Sta., Bull. No. 218 

 (1904). 



Clover mildew, caused by Perotiospora irifoliorum (De 

 Bary), attacks all kinds of cultivated clover and lucerne, also 

 wild leguminous plants belonging to the following genera : 

 Coronilla, Lotus, Lupin us, Medicago, Ononis, and Trifolium. 

 As a rule when a plant is attacked the entire under surface of 

 the leaves becomes covered with a dense, dingy, lilac mildew. 

 Such leaves turn yellow and fall quickly. 



Conidiophores repeatedly branched, ultimate branchlets 

 pointed and slightly curved, conidia elliptical, obtuse, 20-30 

 X 15-20 \x. Oospores globose, smooth, brown, 25-40 /x 

 diam. 



When a crop is once infected the disease spreads rapidly 

 if the weather remains warm and moist, whereas a spell of 

 bright dry weather often stamps out the disease. 



If the pest spreads it is best to cut the crop before oospores 

 are formed and the leaves fall to the ground. 



Beet and mangold mildew {Peronospora schachtii, Fuckel) 

 is responsible for much injury to beet and mangolds. The 

 younger central leaves are most frequently attacked, and in 

 the case of seedlings growth is materially checked or more 

 frequently the plant is killed outright. The mildew appears 

 on the under surface of the leaves as delicate greyish patches. 



