140 Diseases of Truck Crops 



extensively, spraying with Bordeaux 4-4-50 is re- 

 commended for downy mildew {Plasmopara Halstedii) 

 of the Jerusalem artichoke, and for leaf blotch {Ramu- 

 laria cynard) . In damp weather it may be necessary 

 to spray from three to four times during the season. 



DISEASES OF LETTUCE {Lactuca sativa) 



Lettuce is subject to numerous diseases in the field 

 on account of the extreme tenderness of the foliage. 

 None of the diseases to be mentioned should be 

 allowed to gain a foothold in the fields. 



Bacterial Blight 



Caused by Pseudomonas viridUividum Br. 



This is a serious disease, common especially in 

 Louisiana and in other States where lettuce is grown 

 extensively. The disease was first described by 

 Brown ^ who f oimd that large acreages of lettuce were 

 ruined by the blight. The growers at first believed 

 that the trouble was brought about by the use of 

 cottonseed meal.. However, this was proven to be 

 not triie, since the trouble was also f oimd to a very 

 serious extent where no cottonseed meal was used as 

 a fertilizer. The writer has found the same trouble 

 in the lettuce fields in Texas. 



Symptoms. The disease seems to attack only the 



' Brown, Nellie A., U. S. Dept. of Agr. Jour. Agr. Research, 4 : 

 417-478, 1915- 



