6 MASS. EXPERIMENT STATION BULLETIN 248 



germination when spores were wetted by the spray (II and III), especially 

 at the higher temperatures. The data do not suggest that control of the 

 disease can be expected from its use, although Hofferichter (13), Anon. (1), 

 Baehr (2) and Triebels (33) have regarded the product as having merit. 



Sulfuric acid of the specific gravity 1.835-1.840 in a .02 per cent .solution 

 was toxic to spores wetted by the spray and its residue was likewise toxic 

 to dry spores (I). A .01 per cent solution was weakly fungicidal but its 

 residue was inactive. A residue of a .05 per cent solution was lethal to 

 spores applied in the water drop, but residues of weaker solutions were not 

 effective. 



Naphthalene flakes were placed in moist Petri dishes in which dry spores 

 on slides were incubated for germination. The vapors emanating from the 

 deposits were lethal. Naphthalene dust prepared by grinding naphthalene 

 flakes was toxic in water and similar control was obtained with a naphtha- 

 lene-lime dust containing 1 part of naphthalene and 2 parts of lime. 



Schacht's Naphtal-Schwefel is the only dusting material encountered that 

 proved effective by the two methods of study (II, IV). It appeared from 

 these tests to be the most promising dusting material for combating leaf- 

 mold. The product is manufactured in Germany and is recommended for 

 surface mildews. It is a flesh colored powder, lacks the characteristic 

 naphthalene odor and is not wettable with water. On warming or in water 

 with sodium peroxide the naphthalene odor is noticeable. The material con- 

 tains sulfur soluble in CS2, sulfur by oxidation with N&zOz, combined naphtha- 

 lene, CaO probably combined as hydrate and carbonate, and Si02, FcsOa and 

 AI2O3. The naphthalene compound was not identified. 



Dry spores dusted with copper powders (II) germinated normally, but 

 when spores were applied in water drops to the copper deposit, germination 

 was completely suppressed. 



Bordeaux mixtures proved toxic when dry spores were wetted (III) and 

 incubated immediately, but spores which escaped wetting were not affected. 

 When the spray was allowed to dry previous -to incubation (II) germination 

 was not measurably affected. The germ tubes were observed to grow into 

 the surrounding dry Bordeaux residue unaffected. 



Copper sulfate in dilute solutions was toxic. Spores wetted with a .04 per 

 cent solution of copper sulfate were killed and a dry residue of the same 

 spray was lethal to spores applied in the water drop. Spores which escaped 

 wetting (II and III) were not measurably affected. The dry residue of a 

 .04 per cent solution exhibited toxicity to dry spores (I) but weaker dilu- 

 tions did not. 



Copper fungicides possess no merit in the absence of moisture. Williams 

 (38) reported that copper salts are toxic in water and Makemson (22) 

 claimed that Bordeaux mixtures and ammoniacal copper carbonate have 

 little appreciable effect upon either germination or the growth of the germ 

 tubes. In these studies, however, consistent control of germination in the 

 water drop has been obtained. The results substantiate the effectiveness of 

 copper materials on field tomatoes for combating Cladosporium reported by 

 Edgerton and Moreland (10), Edgerton (9), Sherbakoff (30), and Weber 

 and Ramsey (37). Moisture not only influences the growth of the fungus 

 but also favors the activity of copper materials. 



Lime dust was not toxic by either of the two methods of study (II and 

 IV). 



Organic mercury compounds were toxic to spores by methods of study I, 

 II, III and IV. Uspulun was toxic at a .1 per cent strength. Semesan, at 



