190 Diseases of Greenhouse Crops 



The Organism. The mycelium forms a dense net- 

 work of fungal threads within the host tissue. The 

 pycnidia are subglobose, carbonaceous, smooth, 

 slightly papillate, and with a distinct central pore. 

 The pycnidia are scattered and few. 



Leaf Spot 



Caused by Septoria lycopersici Speg. 



Symptoms, The first indications of the disease 

 are minute water-soaked spots on the underside of 

 the leaves. With time, these increase in size and 

 become circular in outline v/ith a definite margin. 

 The spots become hard, dry, dark, and shrunken, 

 and when numerous they coalesce into large blotches, 

 involving the entire leaflets and leaves; the latter 

 soon droop, dry, and cling to the stalk, until broken 

 off by the wind or by any other jar. Within the 

 spots are formed minute black, glistening pycnidia 

 while the spores exude yellowish mucilaginous drops. 



On the stems, the spots are similar to those on 

 the leaves, although they are not so clearly defined, 

 nor do they work in deep enough to form cankers. 

 Spots may also occur on the calyx and on the fruit. 

 The disease, however, is usually a foliage trouble. 

 Of the more resistant varieties may be mentioned 

 Mikado, King Humbert, Wonder of the Market, 

 and Up to Date. Of the medium resistant varieties 

 may be mentioned Alice Roosevelt, President Gar- 

 field, Prelude, Ponderosa, and Magnum Bonum. 



