1«17) DISEASES OF PLANTS. 555 



of media, developing pycnidia. The ascus stage has not been observed. The 

 funiicus appenrs to flourish through a rather wide range of temperature,' growth 

 being vigorous between 25 and 30° C. (77 and 86° F.). The ms'celium is 

 septate and branched. 



Control measures suggested include destruction of diseased parts and 

 cleansing sprays in winter. 



New facts regarding the period of ascospore discharge of the apple-scab 

 fungus, L. Childs {Oregon SI a. Bui. 1J,3 {19 H), pp. 3-11, pjs. 2).— A report 

 is given of a study of the activity of the apple-scab fungus made in Oregon dur- 

 ing 1916 in order to determine the time at which primary infection could be ex- 

 pected and the bearing that it would have on the first application of a fungicide. 

 The investigation has shown that there is a correlation between spore ejection 

 and the prevailing weather conditions, the number of periods of ascospore dis 

 charge, and the length of ascospore activity during the season. 



Mature ascospores were first ejected at Hood River on March 20, 1916, and 

 the last ejection observed was on June 27. At Corvallis this activity was first 

 noted on February 25, and the discharge was abundant as late as May 20, after 

 which no observations were made. It was observed that, as a rule, the heaviest 

 spore ejection occurred during the first two or three days of a rainy period, 

 gradually becoming less toward the end of the wet weather. 



This study is considered to have demonstrated that the delayed dormant ap- 

 plication of fungicides given while the leaves are small and undeveloped can 

 not be safely dispensed with in the Hood River and Willamette Valleys, as the 

 ejection of ascospores begins before the foliage is even started. Owing to the 

 great length of ascospore activity, it is stated that orchardists are not safe in 

 omitting any of the later spring sprayings, even though conidial infections are 

 not present. 



The black knot of plum and cherry, C. B. Hutchings {Ann. Rpt. Quebec 

 Soc. Protee. Plants [efc], S {1915-16), pp. 85-88, fig. i).— Black knot, prevalent 

 in Great Britain, the United States, and Canada wherever wild or cultivated 

 plums and cherries grow, is said to be particularly severe in the ^laritime 

 Provinces, Quebec, parts of Ontario, and New York State. Notable exceptions 

 occur in case of the plum and cherry orchards of the Niagara peninsula, owing 

 to the thoroughness of the control measures there employed. Early removal and 

 complete destruction of all knots before maturing is considered to be the simplest 

 and most effective of all treatments for black knot. 



Rougeot of grapevines, H. Faes {Prog. Agr. et Vit. {Ed. VEnt-Centre), 37 

 {1916), No. 45, pp. Wt-448, fig. 1). — This is chiefly a discussion of the views of 

 several investigators on the grapevine disease known for some years in Switzer- 

 land and elsewhere in Europe and designated by such descriptive names as 

 rougeot, red scald, etc. The evidence is considered to favor the view of Miiller- 

 Thurgau (E. S. R., 30, p. 452) that the disease is associated with the blocking of 

 the vessels by Pseudopeziza tracheipJiila. 



A Pythiacystis on avocado trees, H. S. Fawcett {Phytopathology, 6 {1916), 

 No. 6, pp. 4SS-435; Rpt. Cal. Avocado Assoc., 1916, pp. 152-154) .—The author 

 reports a disease of avocado trees in California in which the bark is killed and 

 slightly sunken areas produced. It is accompanied by the exudation of gum. 

 The disease is said to occur most frequently on trunks not far from the surface 

 of the soil, and it is found not only on the trunks of larger trees but on small 

 seedlings, especially if the latter have been overwatered. 



Studies of the disease showed the presence of a Pythiacystis similar to P. 

 citrophthora, and it is thought that under certain conditions this fungus may be- 

 come at least a wound parasite of avocado trees. The fungus was isolated from 



