DISEASES OF CULTIVATED PLANTS 549 



to growing healthy seedling plants, to 'be followed by soil disinfec- 

 tion. 



Lettuce Rot or Lettuce Drop. This is by all odds the most 

 troublesome disease to the lettuce grower. The plants may rot off at 

 the surface of the earth and the central parts, especially of head let- 

 tuce, may become attacked by the rot fungus (Sclerotinia Liber- 

 tiana). The fungus appears as a whitened covering with a liberal 

 production of spores in clusters. At this station it has not been pos- 

 sible to succeed with the head lettuce because of the rot. Fumigation 

 of house, the use of fresh or steamed earth each year and the careful 

 regulation of temperature and water supply, seem to be the measures 

 most favorable to prevention. A low night temperature, less than 50 

 degrees F. is very desirable, while too high a temperature will usually 

 result in disease. Ventilation is all essential during the day. It is 

 desirable also to gather and burn rotted leaves and plants. 



Leaf-Spot. The leaf-spot fungus (Septoria consimilis) is fre- 

 quent upon wild lettuce plants and occasionally upon outdoor let- 

 tuce, especially in late seasons. The small characteristic leaf-spots 

 are not difficult to distinguish from anthracnose. The remedies are 

 confined to avoidance. 



Root-Rot and Stem-Rot. A bacterial stem-blight has been de- 

 scribed from Vermont, but has not been found with us. A recent 

 stem-rot infection closely resembles rosette in the behavior and form 

 of affected plants. Microscopic examination shows that the stem tis- 

 sues are somewhat brown and that the brown and dead rootlets are 

 occupied by the fungus which is referred to a species of Fusarium. 

 This disease is at present under investigation and should be con- 

 trolled, if at all, by the thorough soil treatments recommended under 

 lettuce rosette. It will be no use to disinfect the houses and then 

 grow plants in diseased soil. 



Tip-burn. Tip-burn of lettuce leaves is often brought to no- 

 tice. Usually it is associated with unsatisfactory watering in the 

 greenhouse, or with extreme changes to summer weather. The rem- 

 edy consists in the methods of watering employed. (Ohio E. S. B. 

 214.) 



ONION DISEASES. 



Onion Blight. How to recognize the disease upon its first ap- 

 pearance is one of the important things for the grower. After the 

 fungus has spread over the entire field and the onion tops are dead 

 or dying, it is no difficult matter for anyone to see that something is 

 wrong. The rapidity with which the disease spreads demands that 

 there be some sign by which we may discover the disease in its ear- 

 liest stages and so be better enabled to cope with it. Unless the crop 

 of the previous year had been badly infested the fungus first appears 

 on a few onions in one or more parts of the field. The first "muggy" 

 weather of July or late June should be the signal for a general look- 

 ing over of the fields to discover any infected plants. The examin- 

 ation is best made in the early morning while the dew is still on tho 

 onions. A diseased leaf is then easily discernible at a considerable 

 distance. Parts of it will appear of a peculiar violet tint, duo to the 



