TOMATO LEAF MOLD 33 



The vaporization of sulfur at regular and close intervals beginning in April in 

 the spring growing season and before planting in the fall season is an efificient 

 contributory method of control. The sulfuring of the heating pipes is not a com- 

 parable method of vaporizing sulfur and ma>- encourage rapid progress of the 

 disease. 



Because of unsatisfactory protection of the lower surfaces of tomato leaves, 

 and conditions peculiar to greenhouse culture, the use of fungicidal spra\ s and 

 dusts is not effective. 



The disinfestation of the greenhouse interior with chemical fumigants is a 

 desirable sanitary measure and should be done just before the finished planting is 

 cleaned out. Burning sulfur and formaldehyde have received the widest recogni- 

 tion for fumigation. The burning of sulfur is customary because it is economical, 

 practical, and lethal to both fungi and insects. 



The usual recommended rate of application of 1 pound of sulfur to 1,000 cubic 

 feet is excessive and invites dangerous chemical reactions with galvanized metal 

 surfaces, iron pipes, and paints containing zinc. The resulting soluble residues 

 in the drip water injure the succeeding plantings. The burning of 4 pounds of 

 sulfur to 10,000 cubic feet under relatively dry conditions is safe. This applica- 

 tion is lethal to tomato leaf mold spores, plant life, and the common insects 

 except the red spider mite. Hydrocyanic acid gas and naphthalene vapois are 

 inert to metal and paint and in strong enough dosages are lethal to red spider 

 mites and eggs but have no fungicidal value. Either should supplement the 

 sulfur treatment to obtain a more complete disinfestation of the greenhouse 

 interior. Paints containing zinc should not be used in interior greenhouse paint- 

 ing, and metal surfaces should be protected with white lead or paints free of zinc. 

 Where sulfur is customarily burned, tinned or uncoated steel trellis wires should 

 be used instead of zinc galvanized iron wires. Dry greenhouse conditions during 

 the sulfur fumigation period should prevail. 



Formaldehyde vapors have a lethal action only on fungi and are inert to metal 

 and paint. Under commercial greenhouse conditions a dosage of 24 fluid ounces 

 of formaldehyde and 20 ounces of potassium permanganate to 10,000 cubic feet 

 is lethal to plants and to tomato leaf mold spores. Cost of the materials in these 

 proportions is about 53 cents as compared with 16 cents for sulfur at the rate of 

 4 pounds to 10,000 cubic feet. 



The dual value of sulfur, its practical utility, and its econom\- lead to its en- 

 dorsement in practice. 



LITERATURE CITED 



1. Anon. New air circulating system promises big gains for greenhouse men. 



Florists Exchange 68(15) :1307. 1928. 

 2. Controlling the deadly leaf mold in greenhouses. Amer. 



Prod. Grower 3 (9):21. 1938. 



3. Revolution in greenhouse ventilation. Market Growers Jour. 



43:752. 1928. 



4. Humidity controlled in greenhouse by new ventilating system. 



Market Growers Jour. 44:204-205. 1929. 



5. Ale.xander, L. J. Tomato leaf mold and greenhouse ventilation. Proc. 

 Ohio Veg. Growers Assoc. 16:87-91. 1931. 



6. Progress report on control of tomato leaf mold. Ibid. 18:53-54. 



1933. 



