4 MASS. EXPERIMENT STATION BULLETIN 248 



exposing the slides to optimum conditions for spore germination. For 

 tests here reported various methods of technique were considered with the 

 view of determining under what conditions control could be expected. The 

 tests were conducted at different degrees of temperature. An outline of the 

 methods of technique used follows: 



Method I. Dry spores were applied with a camel's hair brush to glass 

 slides bearing a dry covering of fungicide. This method of technique simu- 

 lates most closely the conditions obtained on sprayed foliage and offers the 

 most satisfactory means of determining the efficacy of the dry chemical 

 residue in protecting the foliage from infection. 



Method II. Dry spores were applied to clean glass slides which were sub- 

 sequently dusted or sprayed. The spray was permitted to dry previous to 

 incubation. 



Method III. Technique was similar to II except that slides were incubated 

 wet. By methods II and III the efficacy of the sprays as disinfectants was 

 demonstrated, and by II the merits of the dust in preventing germination. 



Method IV. Water drop suspensions of spores were placed on slides cov- 

 ered with the dry fungicide. Where fungicidal activity occurs under the con- 

 ditions surrounding this method of technique it may be inferred that affirma- 

 tive results can be expected on wet foliage in the greenhouse. 



Method V. Glass slides brushed with dry spores were inverted and rested 

 at a distance of 3 mm. above the dry fungicide. This method served to 

 demonstrate the merits of the fungicide as a fumigant. 



Spraying and Dusting Materials. 



Study of Table 1 reveals significant data bearing upon the control of the 

 disease witli fungicides, not considered in previous investigations. As the 

 data show, dusting sulfurs are of no value in preventing germination by any 

 of the methods of testing and under the range of temperatures considered. 

 The data supports Makemson (22) who showed that sulfur dust is of no 

 value, but are contrary to the results of Williams (38) which show that sulfur 

 suspensions and colloidal sulfur are toxic. Barker, Gimingham and Wilt- 

 shire (4) reported that Cladosporium is not nearly as sensitive to sulfur as 

 other fungi. These studies show that sulfur dusting materials are not effec- 

 tive and cannot be expected to offer control of the disease. 



Some toxicity was manifested by Hammond's Grape Dust against spores 

 conveyed in the water drop. This was due to its copper content. The com- 

 position of Grape Dust is sulfur 64 per cent, copper sulfate 2.5 per cent, 

 and inert material not more than 33.5 per cent. 



Hammond's Slug Shot did not control germination in contact with dry 

 spores but in water drops abnormal germ tubes resulted. Hammond's Slug 

 Shot contains gypsum and free sulfur, calcium hydroxide, silica, iron and 

 aluminum oxides, arsenic, less than 1 per cent of metallic copper, less than 

 2 per cent of organic material and traces of nicotine and carbolic acid. 



Schloesing's sulfur, a dusting mixture recovered in the manufacture of 

 artificial gas, also failed under every method of technique. It is a finely 

 divided product and easily wet with water. According to analyses there is 

 present 36.42 per cent total sulfur in the original and 25.44 per cent sulfur 

 in carbon bi-sulfide extract. The ash is highly colored with iron oxide 

 (FesOs). The material also contains phenols and cyanides. 



Herbert and Herbert colloidal sulfur failed by every method of study used 

 to control germination. The concentrated product is strongly acid. A 5 per 

 cent mixture is not toxic. 



