204 MASS. EXPERIMENT STATION BULLETIN 280 



in either case. Other sulfur plots, continued from the previous season, gave 

 satisfactory control of wilt and also retarded growth of the plants, indicating 

 the difficulty attending artificial soil acidification. No further work on this 

 project is contemplated. 



Strawberry Gold Disease. (E. F. Cuba, Waltham). Seed from strawberry 

 plants affected with gold disease produced both diseased and disease-free seed- 

 lings, indicating seed transmission of the disease. Marked stunting and necrosis 

 was associated with seedlings exhibiting this trouble. Experiments show that 

 all the vegetative progeny of "gold" plants acquire the disease. Strawberry 

 beds started with plants from beds free of gold disease remained free; but when 

 new beds were propagated with plants free of the symptoms of the disease but 

 from a source in which the disease was present, its prevalence in the new bed 

 was not reduced. The selection of disease-free plants from a gold-disease source 

 for starting new beds, with subsequent roguing of all plants showing symptoms 

 of the trouble, failed to control the disease. Aside from the systemic nature of 

 this disease, no evidence has been obtained to show the manner of spread. 



Control of Greenhouse Vegetable Diseases. (E. F. Guba, Waltham). 



Tomato leaf -mold. Efforts to control this disease by automatic adjustment of 

 air conditions have been continued. In the fall-winter of 1930-31, 28.6 per cent 

 less leaves infected with leaf -mold resulted with automatic humidity control 

 (relative humidity 80-85 per cent and temperature 60°-73°F.), than with auto- 

 matic temperature control (temperature 60°-65° F.), and the average total yield 

 of tomatoes per plant with automatic humidity control was 1.09 pounds less 

 than with automatic temperature control. 



In the spring of 1931, operation of controls was discontinued after May 15 

 and thereafter all available ventilation was provided. Leaf-mold did not appear 

 until June and eventually all foliage became infected, although the yield was not 

 influenced. The total average jield of tomatoes per plant was 1.64 pounds less 

 with automatic humidity control than with automatic temperature control. 



A smaller amount of infected foliage and a lower yield have been associated 

 with automatic humidity control, while under automatic temperature control 

 and with careful management the prevalence of leaf-mold has never been great 

 enough to reduce the yield. The reductions in yield associated with automatic 

 humidity control appeared to be due indirectly to the higher temperatures needed 

 to effect the desired control of the relative humidity of the greenhouse air. 



A study of the relation of temperature to spore germination and growth of 

 germ tubes is in progress. 



A study of the reaction of a large number of tomato varieties to Cladosporium 

 fulvum Cke. shows differences in the susceptibility. Further work is in progress 

 to determine the feasibility of hybridizing tlesirable market types with t^'pes 

 resistant to h^af-mold. 



A manuscript dealing with the temperature and humidity relations of the 

 causal organi.siii and the relation of greenhouse air management to control of 

 leaf-mold is being prepared. 



Effect on plants of hydrocyanic acid gas after treatment with copper sprays. 

 This work is being done in cooperation with Dr. E. B. Holland of the Chemistry 

 Department. 



Cucumber plants \v(>re n(>ver injured \vh(ni fumigation with hydrocyanic 

 acid gas followed spraying with Corona Copper Carbonate (18 per cent and 50 

 per cent active Cu) or Holland's Basic Coppc>r Sulfate (26 per cent and 53 per 



