686 THE FARMERS 3 HANDBOOK. 



Pea Spot. 



This disease, due to the fungus Ascocltyta pisi (Lib.), attacks French" 

 and haricot beans, garden and sweet peas, hairy vetch, lucerne, and some 

 other leguminous plants. The first indications of disease on the pods is 

 the appearance of pale green spots of variable size and irregular shape. 

 These spots continue to increase in size, and eventually become whitish,, 

 bounded by a dark line, and dotted with minute black points, which are 

 the pycnidia of the fungus and contain numerous spores. The fungus may 

 grow through the pod into the seed, and thus the disease becomes further 

 distributed. The mycelium hibernates in affected seed, reduces the ger- 

 minating power, and carries the fungus over to the succeeding crop* 

 Similar spots may occur on leaves and stem. The spots often penetrate- 

 through the woody part and cause wilting of the plant. 



On young plants the disease often assumes the character of a " damping- 

 off" disease. Spraying with dilute Bordeaux mixture (6 — 4 — 100) on the: 

 first appearance of the disease checks its spread. As the disease is also 

 distributed in affected seed careful attention should be given to the 

 selection of good seed. As in the case of Anthracnose, any spotted seed 

 should be discarded, and all seed should be dipped. It is safer not to obtain, 

 any seed from a source known to have the disease. 



Sclerotium Diseases. 



A disease that is common to very many different plants, including beans- 

 and peas, is associated with the fungus Sclerotinia sclerotiorum (Massee). 

 It attacks the stems, commencing as a white mould at the ground line and 

 working upwards. After the fungus has developed for some time the leaves 

 become yellow, and wilt, and finally the stem collapses owing to the mycelium 

 of the fungus blocking up all the water-conducting channels. When the stem, 

 of the host is hollow the mycelium is produced in considerable quantity in 

 the cavity, and forms numbers of lumps or sclerotia that are white at first,, 

 then black externally. When the stem is solid the sclerotia are formed in itg. 

 substance and become visible on the outside. These sclerotia, which vary in 

 size, some being as large a,s a pea, form a resting stage of the fungus. They 

 remain either free in the soil or in decaying plants, and in the spring develop' 

 small, brown mushroom-like structures on long stems, which produce spores- 

 that are able to infect a new crop. 



Another form of wilt due to Sclerotiwn rolfsii is often met with. This- 

 attacks beans, rhubarb, potatoes, and occurs on snapdragons, carnations, and' 

 other garden plants. The fungus affects the root system, covering it with 

 a felt-like whitish mould which may ascend the stem somewhat. The plants 

 die, and then tiny brown sclerotia, slightly larger than a pin's head, are- 

 found in the webbed growth of the mould. 



Control. — Plants affected with either of these diseases should be burned 

 and not allowed to lie on the ground. The sclerotia lying dormant in the- 

 soil are difficult to deal with. In small gardens the top few inches of soil 

 can be removed and replaced by fresh soil mixed with quicklime. If all 

 infected plants be pulled up and burnt as soon as the first indication of 

 disease is observed, the formation of sclerotia may be forestalled. As an 

 additional precaution it is useful to spray the infected area with Bordeaux 

 mixture (6 — 4 — 50) or with a 2 per cent, blue-stone solution, though the? 

 latter is not practicable on a large area. 



