Lettuce 



101 



in. in the row; grown as a field crop tilled by horse, the 

 rows may be spaced as far as 18 in. For early use start in 

 forcing-house, frame or kitchen. Sow in succession till warm 

 weather. In late summer or September, sowing may be made 

 for the autumn crop. In the South it may stand out over 

 winter and resume growth in spring. Calculate on 1,000 plants 

 for each ounce of seed. Most of the forcing varieties, started 

 under glass are good for early use, as Tenuisball, Boston Mar- 

 ket, Simpson. For summer use, plant varieties that withstand 

 heat, as Deacon, Hanson, Summer Cabbage, Cos. A good com- 

 mercial acre should yield upwards of 30,000 heads. 



Rhizoctonia, or bottom-rot (RJiizoctonia solani) . — Plants 

 in any stage of development may be affected. Rusty slightly 

 sunken areas on the leaf-stalk where it comes in contact with 

 the ground and the total rotting of the leaf-blade are indica- 

 tive of this disease. The entire head may later rot and 

 remain as a blackened erect stump. Frequently the disease 

 causes a damping-off of seedlings. Control: Soil sterilization 

 in the greenhouse will prevent the development of bottom-rot. 

 Thorough drainage and frequent cultivation to dry out the 

 surface soil will reduce somewhat the development of the 

 disease in the field. The more erect types of lettuce are appar- 

 ently less affected. 



Drop, or sclerotinia rot (Sclerotinia Uhertiana) . — Affected 

 plants become water-soaked and collapse with a soft rot in 

 a few hours after showing evidence of this disease. White 

 felts of mycelium with black fungous bodies imbedded in them 

 develop on the under surface of the leaf. This is a serious 

 disease of field and greenhouse lettuce, the seriousness being 

 increased by the fact that the organism will attack almost any 

 host. Control: Thorough soil sterilization, when practicable, 

 will control the disease. Prompt removal of affected plants 

 and drenching the soil with copper sulfate solution has met 

 with considerable success. All refuse should be removed and 

 destroyed. 



Gray mold, or botrytis eot (Botrytis cinerea). — Usually but 

 one leaf or one side of a plant is first attacked. The disease 



