TOMATO LEAF MOLD 7 



that a temperature of 100° F. for 2-3 hours at intervals of a week was offered as a 

 valuable control measure (1); but Small (30) reported that the spores on diseased 

 plants could not be killed by maintaining temperatures above 100° F. for several 

 hours each day, nor when the maximum temperatures were made to reach 110°- 

 130° F. 



In the writer's studies on this question, the conidia were applied to glass slides 

 with a camel's-hair brush and incubated in a dry atmosphere at temperatures 

 of 100°-115° F. for different periods of time. After the designated period of in- 

 cubation, the slides were placed in moist Petri dishes at optimum temperatures 

 for germination to determine the viability of the conidia. It was shown that 

 exposure for 2 hours to a temperature of 115°-116° F. destroyed their viability. 

 At slightly lower temperatures, longer periods of exposure were required to kill 

 the conidia (Table 3). At a temperature of 104° F. this was accomplished within 

 20-22 hours. From the results in Table 3, it is evident that a range of tempera- 

 tures from 104°-115° F. is fatal directly in proportion to the period of incubation, 

 when free spores are exposed. 



Table 3. -Percentage of Germination of Spores of Cladosporium fulvum at 

 Different Temperatures and Periods of Exposure 



tGermination 



-No germination 



Tr. Trace of j,ermination 



Subsequently, small diseased potted plants were exposed to temperatures 

 of 108°-110° F. for different lengths of time. Germination was not affected by 

 an exposure of 2 hours, but was reduced about 75% by an exposure of 4 hours, 

 and about 90% by an exposure of 6 hours. Injury to the foliage, especially tender 

 and diseased areas, occurred in each instance and increased in severity with the 

 duration of exposure. Further experiments were conducted in a greenhouse of 

 1,000 square feet with matured tomato plants on which infection was epidemic. 

 On one occasion temperatures ranging from 105°-110° F. were maintained for 

 2 hours; on another, 118°-123° F. for 3 hours. The plants were injured by the 

 latter treatment but spore germination was not appreciably affected. 



Light 



Light has a retarding influence on the growth of the spore germ tube, and 

 is unfavorable to the best growth of the fungus in culture (13). According to 

 Volk (36), bright light causes a rich growth of spores on the leaves, and darkness 



