16 MASS. EXPERIMENT STATION BULLETIN 248 



foliage and atmospheric conditions under glass, the fungus does not readily 

 lend itself to control with spraying and much less with dusting materials. 

 Spraying is not practicable. A dusting material like naphthalene having an 

 aseptic volatile principle is most promising, but this study has not revealed 

 any materials of such a nature that are effective when applied under com- 

 mercial conditions of culture. Past recommendations appear to have been 

 based on observational evidence which is misleading. The effect of the fungi- 

 cide upon the appearance and flavor of the fruit and the health of the foliage, 

 and the practicability of applying fungicidal materials in a manner to prom- 

 ise control were disregarded. 



Fumigants 



Control of spore germination with naphthalene vapors in Petri dish tests 

 offered encouragement for tests in larger volumes of atmosphere. In a com- 

 partment of the greenhouse of a volume of 5,000 cubic feet, 5 pounds of 

 pure naphthalene flakes were vaporized, by the method described by Hartzell 

 (11), from 12 o'clock noon of March 21 to 7 a. m. of the following day. Slides 

 bearing dry spores of Cladosporium were exposed to the treated atmosphere. 

 After fumigation was completed the slides were removed to moist Petri dishes. 

 Normal germination of spores occurred. Naphthalene did not prove effective 

 under the conditions of the experiment. In another trial the same quantity of 

 naphthalene was vaporized and the same method of exposing spores was fol- 

 lowed, but the effect was negative. In both tests the maximum quantity of 

 naphthalene per unit volume considered safe to foliage was used. The air 

 temperature during the operation was above 80° F. and the relative humidity 

 close to the saturation point. High temperatures were necessary to prevent 

 condensation of naphthalene on the foliage and injury resulting therefrom. 

 The treatments imparted a strong odor of naphthalene to the tomatoes. For 

 this reason neither the vapors nor the dust are applicable to tomato culture. 

 Parker (28) and Speyer (31, 32) claim that tainting is imparted only to ripe 

 fruit and that the naphthalene flavor leaves the fruit within twenty-four hours 

 after picking, when it is exposed to fresh air. Fruit from tomato houses 

 treated with naphthalene materials was unsalable. 



The vapors from a .4 per cent solution of formaldehyde (1-100) are lethal 

 to the spores of Cladosporium (Table 1). A 1-400 mixture is lethal but its 

 vapors are not. Soil disinfection of the greenhouse with formaldehyde 1-100 

 following which the house was closed tight for 24 hours produced an atmos- 

 phere lethal to Cladosporium spores. However, the sterilization of the houses 

 with formaldehyde has not at any time offered any measure of control of the 

 disease on the subsequent crop. The fungus exists in the field and frequently 

 is very prevalent on field tomatoes in Massachusetts. This outside source of 

 the fungus precludes the possibility of obtaining much benefit from soil steril- 

 ization and fumigation of the greenhouse with formaldehyde. 



Sulfur dusting and spraying materials have not given control. The vola- 

 tile principle of sulfur (Table 1, V) is not toxic and dusting sulfur in contact 

 with dry spores does not prevent germination. Sulfur dioxide obtained by 

 burning sulfur is lethal and is an excellent fumigant for this purpose. In a 

 single experiment l^A pounds of sulfur were burned in a compartment of a 

 volume of 5000 cubic feet, in which were growing tomato vines badly infected 

 with leaf-mold. The time consumed for fumigating was five hours. Slides 

 bearing dry Cladosporium spores were distributed in the greenhouse. After 

 fumigation, reaction tests were made of the foliage, wood, metal and glass 

 surfaces. Acidity was strong even in sheltered portions of leaves covered with 



