TOMATO LEAF MOLD 7 



In spite of diligent management the amount of control of the disease can be 

 entirely out of proportion to the added effort and costs, especially when other 

 contributory control measures are disregarded. The sometimes epidemic oc- 

 currence of the disease where late and early heating are practiced is evidence 

 of this fact. Once the disease becomes general on the lower leaves early in the 

 growing period, attempts to check it with heat and ventilation are usually in- 

 effective. For delaying the appearance of the disease or retarding the progress 

 of infection, the practice of ventilating freely from May to October, day and 

 night, and using heat to maintain minimum temperatures between 60° and 65° F. 

 would seem to be ideal. These minimum temperatures are also necessary to 

 promote the steady ripening of the fruit. 



EXPERIMENTS IN CONTROL 



Hand Management and Minimum Temperature Control 



The foregoing information relative to culture and house management was the 

 basis of control demonstrations carried on for several seasons at the Waltham 

 Field Station. Practices recognized as unfavorable to the disease were compared 

 with practices more or less inconsistent with good management and culture. 

 The growing areas were 32 x 32 feet, in different sections of the same greenhouse 

 and separated from each other by glass partitions. The conditions were like those 

 in two adjacent commercial greenhouses e.xcept that the temperatures were 

 regulated by thermostats and not by hand-controlled valves. Under poor manage- 

 ment, warm, stagnant, moist atmospheres were encouraged by neglect of ventila- 

 tion and proper methods of watering. Where good management was practiced, 

 efforts were made to keep the relative humidity of the greenhouse air as low as 

 possible with a minimum temperature bordering 60° F., and not to permit tem- 

 peratures above 70° F. from late April to mid-November without some ventila- 

 tion. Efforts to prevent high relative humidities at night without heat were not 

 generally successful in the early fall and at other critical times, as is evident from 

 a study of the hygrothermographic records in the greenhouse for September, 

 October, and November, as shown in Figure 5A. A comparison of Figures 5A 

 and 5B reveals the influence of boiler heat on relative humidity, but this is 

 usually of small significance in the months from September to November when the 

 outside and inside minimum temperatures parallel each other closely. As the 

 outside temperatures become colder and diverge further from the inside minimum 

 temperature of 60° F., the influence of boiler heat on the relative humidity 

 becomes more marked (Fig. SB) and the development of the disease is retarded. 



The effect of the two methods of management on the control of the disease 

 was determined by a tabulation of healthy and infected leaflets at each pruning. 

 In the fall growing season (1926) 30 percent of the leaflets were infected with 

 leaf mold under poor management and 33 percent under good management 

 (Table 2). The disease was not important enough to influence the yield. In the 

 spring cropping season (1927) 76 percent of the leaflets showed leaf mold under 

 poor management and 19 percent under good management (Table 3). In this 

 season the average yield per plant under good management was 9.24 pounds, of 

 which 8.64 pounds were classed as first grade fruit, in comparison with 8.67 pounds 

 obtained under poor management, of which 7.85 pounds were fruit of first grade. 

 In the fall cropping season (1927) there was no contrast in the amount of disease. 

 It was bad in both houses and there was no heat to permit good management 

 during the early critical period, because of the installation of new boilers. 



