ANNUAL REPORT, 1931 203 



intervals until the plants were killed by frost. The occurrence of the disease 

 here seems to have no relation to summer rainfall. Lack of primary infection 

 rather than failure of the disease to spread would seem to explain its absence. 



There is no positive evidence that the causal fungus, Peronoplasmopara 

 cubensis, ever lives through the winter in Massachusetts. (It is usually present 

 in greenhouses here in the fall and early winter, but has never been seen by the 

 writer on the spring greenhouse crop.) This year, as in earlier years, oospores 

 and other wintering-over stages were looked for, both in green leaves and in 

 leaves killed by the disease and wintered in the soil outdoors, but none were 

 found. As before, no infection resulted from the inoculation of cucumbers with 

 inoculum consisting of cucumber leaves killed by tlowny mildew and buried in 

 the soil in the field during the winter. 



It has often been suggested that the fimgus, wintering-over in Florida, may 

 move northward with the crop and the advance of the season each spring and 

 summer. In 1931, downy mildew was much less severe than usual south of here, 

 notably so in Florida, Georgia, West Virginia, Delaware, and Connecticut. It 

 was present as usual in Connecticut in 1930, but only a trace of it was found in 

 that State in 1931, and that not until about two months after its usual date of 

 appearance in the Connecticut Valley. There was, therefore, a minimum chance 

 of the fungus reaching Massachusetts from states further south. 



Acetic Acid and Pyroligneous Acid as Soil Disinfectants. (W. L. 



Doran). Damping-off was prevented, without injury to germination and with 

 benefit to growth, by soil treatment with acetic acid 1.2 per cent, 2 quarts per 

 square foot, 10 days before seeding. The cost, for a unit area of soil, was three- 

 fourths that with formaldehyde. Damping-off was prevented, with no injury to 

 germination, by vinegar 1 part diluted with 2'^ parts of water (by volume) 

 applied at the rate of 2 quarts per square foot 10 days before seeding. Seedlings 

 of red pine were protected against damping-off, and germination was not injured, 

 by acetic acid 0.8 per cent applied to soil at the rate of % quarts per square 

 foot at the time of seeding. 



Pyroligneous acid, 4 parts diluted with water to a total of 100 parts (by 

 volume), applied to soil at the rate of 2 quarts per square foot, protected seed- 

 lings against damping-off and did not injure seed germination even when applied 

 to soil as late as 1 day before seeding. Per unit area of soil treated, the cost of 

 pyroligneous acid was about 58 per cent of the cost of formaldehyde. The 

 effect of pyroligneous acid on onion smut is now being investigated. 



Eggplant Wilt. (E. F. Cuba, Waltham). Study of the lower limit of toler- 

 ance of eggplant anil its Verticillium pathogene to pH values has been continued. 

 Inhibitory effect on growth of eggplant occurred from aluminum sulfate at pH 

 4.4-4.6, and from inoculated sulfur at pH 3.8-4.0. With aluminum sulfate there 

 was good control of Verticillium at pH values between 4.5 and 5.0, but no control 

 above pH 5.0; with inoculated sulfur there was some control at pH values be- 

 tween 3.8 and 4.8, but no control above pH 4.8. These results are in agreement 

 with those offered in the previous report, and show that the lower limits of toler- 

 ance of eggplant and its Verticillium pathogene to pH values are too close to 

 allow the practical use of sulfur or aluminum sulfate for obtaining the desired 

 range of pH in which control, or partial control, of the disease could be expected. 



In field experiments, an application of one ton of inoculated sulfur per acre 

 lowered the reaction of the soil from pH 6.8 to 6.2. Aluminum sulfate at the same 

 rate of application lowered the reaction to pH 6.4. No control of wilt was obtained 



