TOMATO LEAF MOLD 



29 



Table 18. — Analysis of Residues on Wires and Action of Water Soluble 

 Extracts on Tomato Plants 



Type of Cliaracter of 

 Steel Wire Residue 



Qualitative Test for 



Soluble 

 Material 



Degree of Injury 

 to Tomato Foliage 



Fe Cr Sn Ni Zn SO4 Percent 2.5 percent 5 percent 

 Extract Extract 



Stainless White powdery 



"bloom" Tr 



Bethanized Thick white — 



Tin Coated Thick dark brown + 



Uncoated Thick pale brown + 



Other Considerations 



The rate of burning sulfur has a definite bearing upon the extent of the reaction 

 with metal and zinc paint. In the writer's experiments, dosages ranging from 

 1 ounce to 1 pound of sulfur in a gas-tight greenhouse of 1,500 cubic feet, when the 

 gas was confined for 24 hours, were lethal to the fungus. Under greenhouse condi- 

 tions, 4 pounds to 10,000 cubic feet, divided into two heaps, was lethal to tomato 

 plants and spores of tomato leaf mold, white fly, and aphis. Drip injury to suc- 

 ceeding plantings was reduced to small relative or negligible importance in several 

 large greenhouses where sulfur was burned at this rate, and the growers expressed 

 satisfaction with the destructive elTect of the treatment upon plant life and the 

 common insects. 



While the reaction occurs at small ratio treatments, it becomes even less sig- 

 nificant or negligible if dry conditions are obtained for the fumigating period. 

 In view of the extensive amount of vine and foliage and the moist condition of the 

 soil, high relative humidity and water of condensation are often difficult to avoid. 

 The precaution of allowing the beds to dry off at the end and the use of pipe heat 

 should produce the dry greenhouse conditions necessary to render fumigation 

 safe. 



As a further precaution against drip injury, the poisonous residues on metal and 

 paint can be more or less completely removed by thoroughly hosing down the 

 greenhouse interior with water or with a 5 percent solution of sal soda. The in- 

 fluence of the soda solution on the resulting reaction of the soil suggests a further 

 problem. Since the burning of sulfur at the rate of 4 pounds to 10,000 cubic feet 

 under dry conditions has not produced drip injury of any consequence in various 

 trials observed, there would not seem to be any need for washing down the green- 

 house interior after the fumigating period. 



Formaldehyde Fumigation 



In view of the corrosive action of sulfur dioxide on metal, wires, and painted 

 surfaces in the greenhouse, and the danger of damage to the succeeding crop from 

 the metal and paint drippings, it might appear desirable under some conditions 

 to rely on other materials to eradicate infestations of red spider mite. European 

 reports recommend thoroughly washing down the interior and exterior of the 

 greenhouse with cresylic acid emulsion, phenol solution, or formaldehyde (1,20,36) 

 to kill mites and fungous spores. The greenhouse is tightly closed for about four 

 days to maintain a killing atmosphere and then cleared out. Judging from one 



