1917] DISEASES OF PLANTS. 249 



disease, due to Bacillus tracheiphilus ; angular leaf spot, a new and undescribed 

 bacterial disease ; and downy mildew, due to Peronoplasmopara cubensis. All 

 of these are said to be of rather general and sometimes destructive occurrence. 



Angular leaf spot, a bacterial disease of cucumbers, E. Carsner (Abs. in 

 Phytopathology, 6 {1916), No. 1, pp. 105, 106). — A leaf spot disease of cucumber 

 which has proved to be of bacterial origin is the subject of study in Wisconsin 

 and elsewhere. The disease is characterized on the leaf by rather angular 

 spots bounded by the larger veinlets. The spots at first have a rather water- 

 soaked appearance, later becoming brown and often showing a ragged appear- 

 ance following the breaking away of dead parts. A viscous exudate, becoming 

 on drying a white residue, accompanies the disease, which also appears as lon- 

 gitudinal lesions on the stem. The disease is considered similar to that de- 

 scribed by Burger (E. S. R., 30, p. 648). It is said to be destructive and wide- 

 spread in Virginia, Wisconsin, and Michigan, occurring also in Illinois, Indiana, 

 and Iowa. The causal organism has been isolated and its pathogenicity de- 

 termined. 



From preliminary experiments it is believed that the disease can be held in 

 check by spraying with Bordeaux mixture. 



Steaming of soil for the control of root rot of ginseng, J. W. Brann {Abs. 

 in Fhytopathology, 6 {1916), No. 1, p. 101). — Comparative tests are claimed to 

 show that, from the standpoints of simplicity, cost of operation, and effective- 

 ness, steaming of soil is far superior to the formaldehyde treatment for the 

 control of the ginseng brown root rot. 



The development of Mycosphaerella pinodes in pure culture, R. E. Vaughan 

 {Abs. in Phytopathology, 6 {1916), No. 1, p. 103). — A brief description is given 

 of the characters of M. pinodes observed in connection with pea blight studies 

 carried on at the Wisconsin Experiment Station since 1911 (E. S. R., 29, p. 645). 



Spongospora subterranea and Phoma tuberosa on the Irish potato, I. E. 

 Melhus, J. RosENBAUM, and E. S. Shultz {U. S. Dept. Agr., Jour. Agr. Re- 

 search, 7 {1916), No. 5, pp. 213-254, pis. 9, fig. i).— The results of a study of the 

 geographical distribution and factors governing the occurrence of S. subter- 

 ranea are given, together with information on the relation of the fungus to its 

 various host plants, damage to tubers, relation to soil types, moisture, etc., and 

 control measures. 



The powdery scab is knowTi to exist in six potato-growing sections of the 

 United States, all northern except one which is in Florida, where potatoes are 

 grown as a winter crop. In experiments where powdery-scab-infected seed po- 

 tatoes were planted in 15 localities along the Atlantic .seaboard, no infections 

 were secured, but where soil was shipped from many localities to northern 

 Maine and planted with infected seed, 8 out of 12 lots produced a crop showing 

 powdery scab. Periods of damp, rainy, and cloudy weather, together with poor 

 drainage, are said to favor the development of S. subterranea. Besides the 

 potato, seven other solanaceous hosts of this fungus have been determined. The 

 absence of the canker stage of the disease in the United States is thought to 

 be due to the short growing period afforded the potato crop in the infected 

 districts. 



A study was made of the effect of early harvesting, seed treatment, varietal 

 response, and soil treatment as control measures for the disease, and it was 

 found that early harvesting is beneficial in certain seasons in Maine. Seed 

 treatment with chemicals, especially with corrosive sublimate and formalde- 

 hyde, will reduce the disease. Certain varieties of potatoes escape infection, 

 due rather to differences in development at the time of the infection than to 

 disease resistance, although resistance of varieties has not been fully studied. 



