Lettuce Diseases 151 



symptoms of the disease. The first sign is a wilting 

 of the lower leaves, which is immediately followed 

 by a drooping of upper ones until the entire plant 

 is involved. The affected plant has a sunken ap- 

 pearance as if scalded with boiling water (fig. 27, 

 a.). In examining a dead plant, a white cottony 

 fungus growth is found on the under side of the 

 lower leaves, and near the moist regions at the stem 

 end. 



When the plants are fairly rotted, there appear 

 on the cottony mycelial growth mentioned above, 

 black bodies, or sclerotia, which vary in size from 

 a pinhead to a grain of com. The three definite 

 symptoms of the disease may be summarized: (1) 

 drooping, (2) cottony-like mycelial growth on the 

 under surface of the affected leaves, (3) the appear- 

 ance of sclerotia. The latter help to csnry over the 

 fungus during the winter. After the sclerotia have 

 been in the soil over winter, they germinate in the 

 following spring by sending out small mushroom-like 

 fruiting bodies known as apothecia. The latter con- 

 tain small sacs or asci which bear the spores. 



Control. Lettuce drop is favored by high tem- 

 perature, overwatering, and poorly drained beds, 

 leaky roofs, and insufficient ventilation. To check 

 the disease a low night temperature of 50 degrees 

 F. should be maintained. The water should also be 

 withheld and an abundance of ventilation giren es- 

 pecially during cloudy weather. Soil sterilization 

 with steam or formaldehyde is also recommended. 



