Sweet Pea Diseases 347 



plants, too, may be affected. Such plants linger for 

 some time but are valueless. Corticum vagum is a 

 soil fungus which attacks a number of other green- 

 house as well as outdoor plants. In this case, the 

 organism (fig. 71, c) either produces a damping 

 off among young seedlings, or deep cambium lesions 

 on the stem. With sweet peas the injury is the same. 

 Root rot is introduced in the greenhouse with in- 

 fected soil or manure. Overwatering and a sour con- 

 dition of the soil favor the disease. For a descrip- 

 tion of the causal organism and method of control, 

 see p. 20. 



Root Knot or Nematode 



Caused by Heterodera radicicola (Greef) Muller. 



Symptoms, The disease is characterized by swell- 

 ings on the roots (fig. 70, d.). These are either 

 small swellings formed singly, in pairs, or in strings, 

 thus giving the affected root a beaded appearance. 

 Again, the swellings may be very large so as to be 

 mistaken for root nodules. However, these galls 

 cannot be mistaken for the normal root nodules, be- 

 cause the latter are lobed and are attached at one 

 end, whereas the root gall produces a swelling of the 

 entire surface of the part affected. Infected plants 

 usually linger for a long time, but they can be dis- 

 tinguished by a thin growth and yellow, sickly look- 

 ing leaves and stems. The disease is introduced with 

 infected manure or with compost. For a description 

 of the causal organism and methods of control, see 

 p. 23. 



