22 MASS. EXPERIMENT STATION BULLETIN 248 



Recommendations 



The conditions predisposing to epidemics of leaf-mold occur between May 

 and November in Massachusetts, which obviates the necessity of particular 

 recommendations for each crop. The sj^ring crop is less affected than the 

 fall crop. This crop should run from February to July, inclusive, and since 

 most of the damage occurs late in June and in July the loss is usually small. 

 The spring crop is started in the cold season of the year when continuous 

 heating is required and does not encounter conditions favorable for the 

 development of leaf-mold until the sun's rays become stronger and heating is 

 discontinued. The fall crop is started early in August. During the first 

 two months the sun's rays are intense, the nights are damp, and no heat is 

 used. The ])lants are ex]>osed to the danger of epidemic infection up to the 

 time winter weather appears, or usually until about the middle of November, 

 when continuous heating is required. For this reason the fall crop suffers 

 heavily from leaf-mold, often to the extent of shortening the picking season 

 by IVs to 2 months. Consequently, sulfur should be vaporized In the plant 

 house to guard against infection of the young potted plants. 



Immediately following the setting of the houses a further treatment should 

 be made and then repeated at weekly intervals as long as steady heating is 

 not necessary. The foliage infection counts on the spring crops, and observa- 

 tions on the first appearance of the disease suggest that treatments previous 

 to April are not necessary in Massachusetts. The steady use of heat at 

 night and the mild house temperatures during the day up to this time may be 

 relied upon to keep the disease under control. 



The simple operation of vaporizing sulfur )iy the method advocated in this 

 paper offers a practical and efficient means of combating fungous diseases 

 in greenhouses. The striking control of Cladosporium leaf-mold, otherwise 

 only possible by consistent management of air conditions and the liberal use 

 of heat, suggest remarkable possibilities of the adaptation of this method to 

 the control of other fungous parasites of greenhouse plants. 



SUMMARY 



Sulfur suspensions in water and dusting materials are not fungicidal to 

 germinating spores of Cladosporium fulvum. Lime-sulfur and potassium sul- 

 fide at high concentrations and temperatures show some merit. Copper fun- 

 gicides are toxic in the presence of moisture. Lime is not fungicidal. Schacht's 

 Naphtal-Schwcfel, naphthalene preparations, Uspulun and Semesan are fun- 

 gicidal. Formaldehyde, the oxidation products of burning sulfur, and naph- 

 thalene are toxic fumigants. Hammond's Slug Shot and Hammond's Grape 

 Dust, each containing a small percentage of copper sulfate, have a slight 

 fungicidal efl"ect in the water drop. Sulfuric acid is toxic at extremely low 

 concentrations by all methods of study, and copper sulfate similarly at 

 stronger concentrations. Vaporized sulfur is toxic, but greatest efi'ect is 

 shown in the presence of moisture. 



Control of infection of potted plants inoculated with spores in water was 

 best with copper fungicides, organic mercury, and vaporized sulfur. Lime- 

 sulfur and Hammond's Slug Shot, tested but once, gave favorable control. 

 When the plants were dusted with spores, only vaporized sulfur gave con- 

 sistent control, while Solbar in a single test gave favorable control. 



Only vaporized sulfur has given control of the disease under commercial 

 conditions of tomato culture. Us]iulun and Solbar sprays showed some 

 fungicidal value. 



