990 EXPERIMENT STATION RECORD. 



diseases caused by nematodes, leaf mildews, diseases of (uicurbits, and 

 tomato diseases. 



Among the diseases of lettuce described are the lettuce rot, leaf 

 bhglit, leaf perforation, and mildew. Of these diseases the rot, which 

 is due to Botrytis vulyaris, is the most destructive. Preventive meas- 

 ures, which include sterilization of the houses, the use of fresh eartli, 

 and careful regulation of the temperature, are recommended, and the 

 use of excessive amounts of water should be avoided. Too high a 

 temperature, especially at night when ventilation is not easily secured, 

 is conducive to the development of the fungus. After the rot makes 

 its appearance all aft'ected plants and leaves should be gathered and 

 burned. 



A leaf blight of lettuce was investigated to a limited extent. The 

 affected plants were stunted in their growth and showed numerous 

 small dead areas in the leaves. In general, the symptoms arc those of 

 plants suffering from root diseases, but no exi^lanation was found for 

 the trouble. 



Specimens of diseased lettuce plants were received at the station, in 

 which the leaves of the plants showed numerous ijerforations a milli- 

 meter or more in diameter, with irregular borders. Examination under 

 the microscope showed the presence of a constant fungus, and speci- 

 mens were sent to J. B Ellis, who describes the fungus as Marsonia 

 perforans, n. sp., which is characterized as follows: 



"Spots small, irregular -in shape, 1 to 2 pi in diameter, pale, soon 

 deciduous. Acervuli 100 to 120 /< in diameter, or by confluence larger. 

 Conidia abundant, clavate or wedge-shaped, hyaline, faintly unisep- 

 tate, 11 to 15 by 2i to 3 /< exceptionally reaching 20 /< long." 



The disease is regarded as a serious affection of greenhouse lettuce, 

 but the extent of injury likely to result from the leaf perforation is 

 not known. 



The downy mildew of lettuce, caused by Breniia lactucm, is briefly 

 described and preventive measures suggested. 



Nematode diseases on various ornamental and other plants are 

 described, and the remedial treatment recommended is sterilfeation 

 either by freezing or steaming all of the earth used in the green- 

 house. 



, Brief notes are given on leaf mildews and spraying with fungicides 

 under glass. The powdery mildew of composite plants has been suc- 

 cessfully combatted by the use of i)otassium sulphid solution, 1 oz. to 

 3 gal. of water, or copper sulphate solution of the same strength. 

 Three or four applications have proved sufficient to eradicate the 

 disease. 



The favorable influence of a weak Bordeaux mixture for the preven- 

 tion of carnation leaf spot and leaf mold is mentioned. Applications 

 of the same fungicide as well as Fowler's solution upon i)lants attacked 

 with rust gave negative results. 



Among the diseases of cucurbits the bacterial blight, due to BaciUuK 



