Vegetable and Field Crops 



197 



ing originally often $1000 per acre — and thus destroy their 

 value for lettuce culture. The damage is thus much more 

 than injury wrought merely to the current crop. 



The sclerotia, when favorably situated, are capable of 

 germination, each producing several trumpet-shaped organs 

 (Fig. 106), with stems about 15 mm. long and disks 3-8 mm. 

 or less in diameter. Spores, capable of initiating the fungous 

 growth upon dead or sick lettuce tissue, issue in great num- 

 bers from these disks, and from material thus infested the 

 fungus can make its way into the healthy lettuce plant. 



Fig. 106. — Sderotia of Sclerotinia from lettuce germinating. 



If all infected plants be pulled and burned as soon as the 

 first indication of disease is observed, the formation of 

 sclerotia will be prevented. As an additional precaution 

 it is well to spray the areas occupied by diseased plants 

 thoroughly with Bordeaux mixture or bluestone solution. 



A few years of such procedure will much reduce the in- 

 fection or perhaps eliminate it entirely. All lettuce trash 

 should be removed from the beds, since it serves as the ini- 

 tial point of attack for the fungus. Growers whose land is 

 free from the disease should guartl against its introduction 



