202 MASS. EXPERIMENT STATION BULLETIN 280 



An application of sulfur (500 pounds per acre) to a field, the soil of which had 

 an initial pH of 6.4, lowered the pH value to 6.1, but this was insufficient to 

 prevent infection of tobacco by Thielavia, and growth of plants was not affected. 

 Yields of tobacco have been increased consistently when sulfur has been applied 

 to a soil infested with Thielavia if the pH value of this soil was lowered by the 

 sulfur to below 5.9, but not otherwise. 



Liming was without any effect on the fire-holding capacity of the tobacco 

 grown in 1929. In the case of the crop of 1930, the burn of the darks was im- 

 proved, but the burn of the seconds was not affected by lime. Sulfur (400 pounds 

 per acre) did not reduce the fire-holding capacity of the leaf grown in 1930. Burn 

 of the darks was better in plots in which tobacco was grown every year than in 

 plots in which tobacco followed timothy or alfalfa. 



In 1930, the quality of tobacco grown in limed plots was as good as that in 

 plots not limed. In earlier years, both yield and quality of tobacco have been 

 lower in limed plots. 



In pot experiments, soil pH values were not significantly lowered by alum- 

 inum phosphate alone, and they were lowered as much by sulfur alone as by sul- 

 fur with aluminum phosphate. When these treatments were applied to soil 

 infested with Thielavia basicola, the severity of black root-rot was reduced and 

 growth increased as much by sulfur alone as by sulfur and aluminum phosphate 

 together. 



Brown Root-Rot of Tobacco. (W. L. Doran). With the cooperation of 

 H. D. Ilaskins, it was found that soils in which brown root-rot was most severe 

 were characterized by high water-holding capacity, high content of clay and 

 silt, and low content of sand. Soils in which brown root-rot was mild or from 

 which it was absent, were characterized by high content of sand, low water- 

 holding capacity, and low content of clay and silt. No consistent relation was 

 found between the severity of brown root-rot and pH value of soil, soil content 

 of organic and volatile matter, total nitrogen, nitrate nitrogen, or iron and 

 aluminum oxides soluble in water. 



The effects of ammonium thiocyanate on brown root-rot and growth of to- 

 bacco are being investigated. 



Onion Diseases and the Use of Fungicides on Onions. (W. L. Doran). 

 As in earlier years, this work was done in cooperation with A. I. Bourne. There 

 was no downy mildew, but blast was severe in 1931, appearing, as in 1927 and 

 1928, about the third week of July. 



The onset of blast was delayed, but not prevented, by spraying with Bor- 

 deaux mixture. Yields were increased somewhat, however, in all plots sprayed 

 4 times with Bordeaux mixture. As in the previous three years, copper-lime dust 

 was of no benefit. 



Growers who find the ownership of a power sprayer feasible, and who spray 

 onions with nicotine sulfate for thrips, may, on the basis of the results of these 

 experiments, expect some further increase in yield if Bordeaux mixture is used 

 with nicotine sulfate; but there is no e-\adence that the purchase and use of a 

 power sprayer solely for the application of Bordeaux mixture to onions would 

 be profitable in the average year in Massachusetts. 



A report of this work has l)een published in Bulletin 279. 



Downy Mildew of Cucumbers. (\V. L. Doran). In each of the six years 

 ending in 1930, this disease has always occurred in Massachusetts; but it was 

 not found in 1931, although many fields of cucumbers were examined at weekly 



