TOMATO LEAF-MOLD 17 



the leaf-mold fungus. Spores on glass slides exposed to the fumigant were 

 killed, and twelve mounts of spores obtained from the treated vines gave no 

 germination. Qualitative tests of the mold on the leaves gave strongly acid 

 reactions. Spores collected previous to fumigation germinated excellently. 

 The fumes of burning sulfur are extremely lethal and penetrating. The prac- 

 tice of burning sulfur before planting tomatoes is an economical and effective 

 means of destroying the fungus and safeguarding the future crop from an 

 inside potential source of attack. 



Vaporized Sulfur 



Methods of Vaporizing. 



Sulfur on heating pipes. The practice of treating the heating pipes with 

 sulfur powders, pastes and liquids prevails among growers of greenhouse 

 plants. It is considered a practical means of controlling certain fungous 

 diseases but has its limitations. In California, because of its mild climate, 

 steam pipe surface in greenhouses is small and very little heat is used, as a 

 result of which the sulfur treatment of the pipes cannot be relied upon to 

 control cucumber powdery mildew, according to Milbrath (2.5). In Massachu- 

 setts, varying results have been obtained in projjortion to the area of pipe 

 surface treated and the temperature of the pipes. The value of the practice 

 is very much in dispute among commercial growers. Observations in tomato 

 houses where the practice has been rigidly followed for controlling leaf-mold 

 indicate that it is of doubtful value. According to Parker (27) and Hoster- 

 mann (14) the sulfur treatment of the heating pipes is not safe at high pipe 

 temperatures. The danger lies in the production of sulfur dioxide, sulfurous 

 and sulfuric acid in sufficient volumes to cause injury to the growing plants. 

 These sulfur oxidation products also have a corrosive action on the pipes, and 

 the scale which forms interferes with the radiation of heat. Pipes treated 

 repeatedlj' are not considered lasting, and some growers dislike engaging in 

 the practice for that reason. For practical reasons the sulfuring of heating 

 pipes is restricted to the colder months when heat is used. Since the con- 

 ditions which favor the development of tomato leaf-mold to the extent of 

 causing yield reduction appear usually between the latter part of May and 

 the middle of November, in Massachusetts, when little or no heating is 

 practiced, the use of special heating units for vaporizing sulfur would be 

 extremely economical and desirable. 



Mechanical sulfur vaporizers. The vaporization of sulfur with oil stoves 

 has been recommended by Bailey (3), Humphrey (15, 16), Norton and 

 White (26), Maynard (2-1) and others for controlling powdery mildews. The 

 apparatus suggested was never received with favor by growers of green- 

 house plants in spite of the effectiveness of the practice. The oil stoves were 

 not adaptable for operation in large houses, and in small houses where effec- 

 tive results could be realized ignition of the sulfur occurred frequently. The 

 small quantity of sulfur discharged, often giving unsatisfactory control, the 

 danger of its ignition, the necessity of keeping constant watch of the appar- 

 atus, and the lack of adaptation of such apparatus to commercial establish- 

 ments led to its disfavor. More recently Campbeirs Patent Sulfur Vaporizer 

 has been used to a limited extent. In the construction of this apparatus 

 provision was made to exclude the oxygen of the air while vaporization is in 

 progress, the purpose being to prevent ignition of the sulfur which, however, 

 it fails to do. Its operation is extremely dangerous to plant life and unprac- 

 tical for commercial purposes. 



