16 MASS. EXPERIMENT STATION BULLETIN 203 



treatment. The length of time toxicity persistefl was not shcrtened Ijy tlie supple- 

 mentary use of ferric chloride. 



Calcium cyanide applied to soil at rates up to 1800 pounds per acre did not pre- 

 vent infection of tobacco by Thielavia. Heavier applications reduced the severity 

 of infection without increasing soil acidity, but were toxic to plants. 



Brown Root-Rot of Tobacco. (W. L. Doran.) When this disease developed 

 following timothy in a cropping system, it was usually more severe in clay soils 

 than in sandy soils. The addition of timothy to a soil was sometimes beneficial 

 to tobacco, the benefit being greater in sandy soils than in clay soils. In 

 general, timothy when followed by brown root-rot of tobacco was less harmful 

 in sandy than in clay soils; and timothy when it did not result in brown root-rot 

 of tobacco was followed by better growth of tobacco in sandy than in clay soils. 



Disease Resistance of Potato Varieties. (W. L. Doran.) The varieties 

 Green Mountain, Katahdin, and Foster's Rust-proof were compared. There was 

 no late-blight and there was little or none of the virus diseases. The season was 

 dry and there was much injury of Green Mountain and Katahdin by drought, 

 tip burn, and insects (aphis and leafhopper). Under these conditions, Foster's 

 Rust-proof was much more resistant and long-lived than either Green Mountain 

 or Katahdin. 



Downy Mildews of Cucumbers and Lettuce. (W. L. Doran.) Downy 

 mildew of cucumbers {Peronoplasmopara ciibensis (B. & C.) Clint.) was not ob- 

 served here in 1931, but it appeared on August 18 in 1932. This is the latest re- 

 corded date of its first appearance here in any year. An account of investigations 

 of this disease by the writer has been published recently in Bulletin 283. 



It was found that resin has a markedly fungicidal effect on P. ctibensis. A 

 stock solution was made of resin 5 parts, wood alcohol 5 parts, and potassium 

 hydroxide 1 part. This was then diluted with water so as to contain resin in the 

 proportions indicated below. Infection of cucumber plants, sprayed with resin 

 solutions previous to inoculating with P. ciihensis, was entirely prevented by 

 resin 1:150 and reduced to only a trace by resin 1:200. There was no injury to 

 cucumber plants by resin 1:150, although they were slightly injured by resin 

 1:100. 



Downy mildew of lettuce {Brcniia lactucae E. Regel) was severe on the variety 

 Bel-May in greenhouses in April 1932, although this variety had been previously 

 considered relatively resistant. 



The resistance of certain varieties of lettuce was shown by the average number 

 of plants which became infected out of each 100 plants inoculated with B. lactucae. 

 These were as follows: Dreer's Wonderful, 25; Sutton's Golden Ball, 24; Rosy 

 Spring, 3; Dreer's Iceberg, 1 ; Loos Tennis Ball, 0; Loos Tennis Ball (Vilmcrin's), 0. 



Germination of the conidia of this fungus was prevented when the conidia, in 

 water, were placed on micro-slides which had been sprayed with resin 1:100. A 

 0.25 per cent solution of sodium tetraborate (borax) similarly used was likewise 

 effective in preventing germination. Aidiydrous sodium carbonate was ineffective 

 at the concentrations used. 



With over 90 per cent of these conidia germinating in water, less than 10 per 

 cent germinated in a 1 per cent water solution of the exudate from cut stems of 

 lettuce plants. 



Sporulation oiB. lactucae was entirely prevented by dusting infected plants with 

 sulfur dust. Copper-lime-arsenic dust was nearly as effective. 



Eggplant Wilt. (E. V. Guba, Waltham.) Growth of Verticillium in culture 

 occurred at a range of 50°-95° F., with the optimum at 78°. The best growth of 



