ANNUAL REPORT, 1930 243 



Onion Blast (L. H. Jones). By artificially controUiiifi' the environment 

 of growing onions, it was possible to produce an injury to the plants re- 

 sembling blast. Reduced light, high relative humidity, and a wet soil for 

 a period of ten days was sufficient to make the plants blast when exposed 

 for a few hours to intense sunshine and an atmosphere of low relative 

 humidity. Absence of bla.st in the field this year precluded the possibility 

 of comparison with that condition as it occurs naturally. 



Eggplant Wilt. (E. F. Guba, Waltham). Since the last report, study 

 has been confined to the pH relations of the causal organism and host. 

 On .slides in Petri dishes aluminum sulfate in 1-100 to 1-500 dilutions, 

 inoculated sulfur, and monohydrated copper-lime dust (20-80) destroyed 

 the viability of the spores. Nutrient media acidulated with sulfuric acid 

 completely inhibited growth of the pathogene at pH 3.7, and the rate of 

 growth increased in proportion to an increase in the pH value of the grow- 

 ing medium. Retardation of growth occurred below pH 4.5. However, the 

 increase in growth of the pathogene due to but slight decreases in acidity 

 between pH -i.O and 4.5 was significant. 



Aluminum sulfate and inoculated sidfur were compared with respect 

 to their effect upon the growth of eggplants and the control of the 

 disease. Wooden boxes holding four gallons of soil were used and the 

 acidifying agents were added in increasing quantities. Inocidated sulfur 

 produced a rapid increase in acidity, while at least three times as much 

 aluminum sidfate was required to obtain the same eft'ect. AVith aluminum 

 sulfate, a range of pH 4.7-5.0 showed no effect upon the growth of egg- 

 plants. Infection occurred at pH 5.0 and higher. Below pH 4.7 growth 

 became poorer as the pH value of the soil decreased. With inoculated sul- 

 fur, all of the plants were infected at a soil pH of 4.3, and one-third of 

 them at pH 4.0. At pH 4.0 growth was fair, and at pH 3.5-3.6 the plants 

 were killed. 



The effect of field applications of chemicals on the control of the disease 

 and the growth of the host was studied. The plants were grown in soil 

 sterilized with formaldehyde, and the field to which the chemicals were 

 applied had been used for eggplants for four years in succession. The 

 results revealed the failure of inoculated sidfur and aluminum sulfate 

 to control the disease when applied at a rate in excess of the tolerance of 

 the host. No results were secured which could be construed as a basis for 

 suggesting acidification of infested soil as a method of controlling egg- 

 plant wilt. In the experiment reported, eggplants on land in sod for five 

 years gave the best growth and the best yield in spite of the high per- 

 centage of infection. The existing practice of using old sod for egg- 

 plants remains the only reliable and practical method of control. 



Cucumber Downy Mildew. (W. L. Doran). The weather of the season 

 seems to have little relation to the date of the first appearance of this disease 

 in the field. In six consecutive years (1925-1930), downy mildew has always 

 appeared here within the first two weeks of August. 



Bodies resembling oospores have been found, but attempts to germinate 

 them or cause infection with them were without result. The means of over- 

 wintering of Peronoplasmopara cubensis, therefore, remains undertermined. 



It was found that conidia produced in any dewy night do not live after 

 the svm dries the dew in the morning. Infection in the absence of rain, there- 



