154 DISEASES OF TROPICAL PLANTS CH . 



" brown spot," which can be readily distinguished from 

 the above by concentric markings. 



(/) Septoria nicotianae, Pat., is the cause of a 

 leaf-spot disease which has been reported from Jamaica. 

 It is known as the frog-eye, and appears as concentri- 

 cally zoned brown spots which finally become white. 



The only remedial or precautionary measures that 

 can be taken to advantage, are the protection of the 

 plants in the seed beds, with Bordeaux mixture if 

 necessary, and to transplant none but healthy plants. 

 A single diseased plant may cause the serious injury 

 of a great many. 



Mildews. Both the powdery mildew (Erysiphe 

 communis (Wallr.), Lev.) and the downy mildew 

 (Phytopkthora nicotianae, De Haan) are reported from 

 Java and Australia, and probably have a much wider 

 distribution. 



Either the same or a different species of Erysiphe 

 has been reported as being a very severe pest in 

 Dumbara, where it is known by the local names of 

 "Ash" or "Alu" or " Sambal." It attacks the lower 

 leaves and gradually works upwards, completely covering 

 them with a white mycelial and conidial growth which 

 gives them the appearance of being covered with ash. 

 The leaves become dry but retain their ash character 

 even after curing. Unfortunately the disease also 

 attacks the tomato, red pumpkin, seedling tamarind, 

 and many other plants, both cultivated and wild, which 

 increases the difficulties in combating it. It can 

 doubtless be controlled to some extent by the use of 

 such spraying mixtures as the ammoniacal copper 

 carbonate solution or some other preparation which 

 does not stain the leaves. 



Peronospora nicotianae, Speg., is the cause of 

 another mildew which has been reported from Queens- 

 land and California. It forms dirty, greyish violet 

 tufts on the under surface of the leaves. It can be 

 controlled by the use of Bordeaux mixture. 



Granville Tobacco Wilt. There have been reported 



