32 MASS. EXPERIMENT STATION BULLETIN 361 



SUMMARY 



In Massachusetts, tomato leaf mold, due to the fungus Cladosporium fidvum 

 Cke., is of importance only in greenhouse culture. Its occurrence is associated 

 with the off-heating or warmest season of the year when the mean maximum 

 relative humidity and temperature are highest and when the difference between 

 the inside and outside mean minimum temperature is least. 



The successful control of the disease involves cultural practices, greenhouse 

 management, greenhouse location and design, and the use of chemicals for the 

 disinfestation of the greenhouse interior and the protection of the plants from 

 infection. 



Light and free circulation of air contribute to the control of the disease. These 

 conditions are promoted b\' the proper spacing of the plants and pruning. 



Careful bottom-watering makes for dry foliage and is an aid to the control 

 of the disease. Overhead watering or watering with the open hose should be 

 avoided. Watering should be done in the morning and on bright days to insure, 

 so far as possible, dry conditions at night. 



Ventilation to prevent abnormal atmospheres such as high temperatures, stag- 

 nant air, and high relative humidity is intimately bound up with the problem 

 of control. The need for adequate ventilating area on all sides and both spans 

 of the greenhouse is imperative in tomato culture to permit the closest approach 

 to normal or outside atmospheres during the off-heating or critical season. 



Heat employed intelligently with ventilation late in the spring and early in 

 the fall season of growing can dela}- the progress of disease, or through careless 

 use may readily encourage an epidemic. 



Heat and ventilation to maintain inside minimum temperatures of 60° to 65° F. 

 as the outside temperatures drop to 50° late in the spring and early in the fall, 

 and full ventilation at other times during the milder critical months would appear 

 to be the most economical method of control. During the heating months, 

 periods occur when the outside temperatures converge closely upon the inside 

 minimum growing temperature of 60° F. and render control of the relative hu- 

 midity difficult. Otherwise the wide difference in temperature and the resultant 

 influence on the relative humidity explain the absence or slow development of 

 the disease in the colder months of the >car. Condensation of moisture from the 

 air as dew and guttation from the plant itself contribute to the progress of the 

 disease and can be prevented by cultural and greenhouse management practices. 



Good management in contrast to poor management controlled the disease 

 rather well in some seasons, but in others was less effective. 



Several automatic or mechanical systems of air conditioning are described. 

 Controlled relative humidity below 85 percent within a temperature fluctuation 

 of 60° to 75° in conjunction with forced air was contrasted with a minimum fi.xed 

 temperature of 60° F. and hand ventilation. Better disease control under the 

 automatic humidity control was not accompanied by better yields, and the in- 

 stallations were too expensive to warrant commercial use. A constant minimum 

 temperature control has many advantages over hand control and is worthy of 

 installaticni in commercial practice. 



Control of the disease is int iniatch' bound uj) with greenhouse location and 

 design. Location with regard to good air circulation is an important aid to suc- 

 cessful management. 



