30 MASS. EXPERIMENT STATION BULLETIN 361 



report the washes are the more modern method of disinfestation; but according 

 to a more recent report the treatment is apparently no more efficient than sulfur 

 dioxide in destroying the mites in crevices and cracks. Under our conditions the 

 disinfestation of the vines and interior with a wash before clearing out would be 

 difficult and impractical and is not justified in view of the efficiency of such fumi- 

 gants as naphthalene and hydrocyanic acid gas which, unlike sulfur, are inert to 

 metal and paint even at high dosages. Both eggs and mites succumb to these 

 treatments. 



Both naphthalene and hydrocyanic acid gas, even when generated in large 

 excess, are inert to the spores of the tomato leaf mold fungus. In two separate 

 experiments in a tight greenhouse of 1,500 cubic feet, Cladosporium spores were 

 exposed to 8 ounces of vaporized naphthalene for 72 hours at a temperature of 

 70° to 80° F. and to 16 ounces for 4 days at a temperature of 80° to 86° F. In 

 the latter case there was a heavy deposit of naphthalene on the glass, but this had 

 all disappeared at the end of the 4-day period. There was no lethal effect on the 

 spores. In the same volume of atmosphere, hydrocyanic acid gas was generated 

 from sodium cyanide (10.6 grams), sulfuric acid (16.5 c. c), and water (22.5 c c.) 

 and confined for 48 hours. In nmltiples of this dosage up to 15 times, not the 

 least effect was shown on the viability of the spores of Cladosporium fulvum Cke. 

 and Botrylis cinerea Pers. These results are in line with the generally accepted 

 view that naphthalene and hydrocyanic acid gas lack fungicidal value. When 

 either of these insecticides is used, it would seem desirable to fumigate further 

 with a fungicide to complete the disinfestation of the greenhouse interior. The 

 burning of sulfur in small dosages, not in excess of 4 pounds per 10,000 cubic 

 feet, is lethal to fungous spores and most insects, and is justified in view of its 

 negligible cost and practical use. Where a definite prejudice against sulfur exists, 

 formaldehyde fumigation may be substituted. 



The findings and opinions as to dosages of formaldehyde gas lethal to the 

 spores of the tomato leaf mold fungus are quite inconsistent as may be noted 

 from a study of Table 19. In addition, Williams (54) noted that the fungus in 

 culture was killed on exposure to formaldehyde vapors for one hour and that 

 spores exposed for 8 hours were killed, but the concentration of the gas was not 

 stated. 



Table 19. — Concentrations of Formaldehyde Reported to be Toxic to 

 Spores of Cladosporium fulvum Cke. 



(Amounts per 1,000 cubic feet.) 



Authority Form- Perman- 



aldehyde ganate of 



Fluid Potash 



Ounces Ounces 



Makemson (26) 48 23 24 hours Not lethal 



Small (44, 46) 3.2 2 Not stated Almost completely 



lethal 



Parker {ii) 5 24 hours Good results 



Van der Meer (52) . . 1 l^ Not stated Minimum toxic dose 



in laboratory 



