TOMATO LEAF MOLD 31 



Some tests were conducted in a gas-tight greenhouse of 1 ,500 cubic feet. Tomato 

 leaves bearing the fungus were exposed for 24 hours. The reacting chemicals 

 were used in increasing amounts from 2 to 10 fluid ounces of formaldehyde with 

 L6 to 8.3 ounces of permanganate of potash. All dosages were lethal to the spores 

 of the fungus. In a greenhouse of 10,000 cubic feet, ratios as low as 24 fluid ounces 

 of formaldehyde and 20 ounces of permanganate of potash, with ventilators closed 

 for 24 hours, killed both spores and plants. This appeared to be the minimum 

 lethal dosage under greenhouse conditions, since ratios of 20 fluid ounces of formal- 

 dehyde and 17 ounces of permanganate of potash to 10,000 cubic feet, and lower 

 ratios, were not generally toxic to the fungus. In a greenhouse of 31,000 cubic 

 feet, 96 fluid ounces of formaldehyde and 80 ounces of potassium permanganate, 

 which is stronger than the 24-20-10,000 ratio, were lethal to Cladosporium spores 

 and tomato plants but not to the greenhouse white fly. For houses that leak 

 more or less, a ratio slightly higher than the recommended dosage is desirable. 



In fumigating with formaldeh\de gas, vessels of rather large volume are nec- 

 essary to guard against overflow of the foaming liquid during the reaction. A 

 5-gallon vessel about 8 inches in diameter for each 10,000 cubic feet is suggested. 

 The vessels should be narrow enough so that the crystals of potassium perman- 

 ganate are covered by the formaldehyde. The required amount of liquid is 

 placed in each container. The required amount of potassium permanganate is 

 weighed out in paper sacks and set beside each container. These are added to 

 the vessels, beginning with the one farthest from the exit. A quiet atmosphere is 

 desirable for an effective fumigation and the greenhouse should be closed tight 

 for 24 hours. 



The cost of fumigating 10,000 cubic feet of greenhouse with formaldehyde 

 at the suggested ratio is about 53 cents as compared to 16 cents for sulfur on the 

 basis of 4 pounds to 10,000 cubic feet. In view of the large difference in cost and 

 the lack of insecticidal effect from formaldehyde, the burning of sulfur in small 

 amounts for fungicidal purposes seems preferable. For a more complete kill of 

 the red spider mite, a supplementary fumigation with either naphthalene or hydro- 

 cyanic acid gas is recommended. Formaldehyde, naphthalene, and hydrocyanic 

 acid gas are inert to paint and metal but lack the merit of a satisfactory disin- 

 festant in being only either fungicidal or insecticidal. 



Chemical Soil Sterilization 



Formaldehyde when used as a soil sterilizing agent produces a greenhouse 

 atmosphere lethal to fungous spores. Carbon disulfide emulsion when used on the 

 soil to kill soil-infesting nematodes produces an atmosphere that is lethal to most 

 insects. The application of both chemicals in combination to eradicate soil- 

 inhabiting fungi and nematodes produces a strongly lethal greenhouse atmosphere. 

 To obtain a thorough fumigation, the concentration of these gases should be 

 maintained for two to three days by keeping the ventilators tightly closed. ^ 

 Since soil-sterilizing chemicals are applied after the plants are cleaned out, the 

 fumigation of the interior resulting from chemical soil applications does not do 

 what is accomplished by the disinfestation of the old infested vines. 



•■"The use of these chemicals for sterilizing greenhouse soil is described in Mass. .-^gr. Expt. Sta. 

 Jul. 292, "Carbon Disulfide Emulsion for the Control of the Root-Knot Nematode." 



