VEGETABLE AND FIELD CROPS 243 



at this time, dense, cotton-like growths of myceUum, and in 

 later stages small black, irregular bodies, the sclerotia, 

 which vary from 3-10 mm. long, somewhat less in thick- 

 ness. The sclerotia and the mycelium are unmistakable 

 signs of this disease. 



Sclerotiniose was first definitely recognized in America 

 in 1900, though it doubtless did much damage before then. 

 It has since then followed the rapidly extending lettuce in- 

 dustry into many states and is particularly destructive in 

 the South Atlantic seaboard states from Virginia to Florida, 

 where its inroads upon the crop grown under cover are es- 

 pecially damaging. The causal fungus may persist from 

 year to year as sclerotia in beds once infected, — beds cost- 

 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 present crop. 



The fungus passes from one season to the next, as the 

 sclerotia which, favorably situated, are capable of germina- 

 tion, each producing several trumpet-shaped organs, 

 Fig. 110, with stems about 15 mm. long and disks 3-8 imn. 

 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 infected the 

 fungus can make its way into the healthy lettuce plant. 



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 ]:)recaution 

 it is well to spray the locus of the diseased plant 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 



