DISEASES IN GREENHOUSE 97 



collar rot has become established, steriliza- 

 tion of the soil is the only remedy. Sweet 

 peas grown in the greenhouse are subject 

 to moisture conditions quite different from 

 those grown outdoors. Natural light is 

 less in winter, and in order to induce 

 growth under adverse conditions heat is 

 used as a stimulant. This produces plants 

 readily susceptible to disease. As these 

 difficulties cannot be avoided, it is essen- 

 tial to start with sterilized soil in the 

 benches. 



Most sweet pea growers do not change 

 their greenhouse soil every year. As time 

 goes by, and the crop is grown successively 

 in the same place, the soil soon becomes 

 sour. This condition naturally tends to 

 encourage the development of a parasitic 

 florg in the soil which is detrimental to 

 sweet pea culture. 



The following is a quick method to de- 



