82 PROTECTION OF PLANTS, 1921-22 



attack vascular tissues but by rapid multiplication the bacteria plug up the 

 xylem thus preventing the upward passage of water and accounting for the 

 rolling of leaves, rosette top and wilting. 



As to the organism causing the disease it is highly probable that more than 

 one maj' give rise to similar symptons. Morse inclines to the view that in 

 Maine it is B. atrosepttcus van Hall. This typically attacks stems but does not 

 cause excessive tuber rot. Harrison, from Ontario material, described B. sola- 

 nisaprus which caused severe tuber rot in addition to black stem rot. This 

 was the first description of such a disease in America. It has since been found 

 in Michigan (Fig. 6) but is ascribed by Coons to B. atrosepticus van Hall. In 

 the Western and irrigated parts of the United States an organism causing a sim- 

 ilar tuber rot and stem-rot is ascribed by Shapovalov and Edson to B. phytoph- 

 thoriis Appel. 



Control 



Whatever the specific organism it is reasonably certain that in Canada it 

 cannot overwinter in the soil. Hence it is to the seed tuber that one must look 

 for control. The chief points to bear in mind are: 



1. To select sound tubers for seed. 



2. If it is impossible to guarantee the soundness of the seed tubers then 

 treat with formaldehyde — 2 pints in 30 gallons of water at 119 deg. F. to 122 

 deg. F. for two minutes. The tubers are then covered for one hour and dried. 

 This treatment is recommended only as a good general measure since it is 

 obviously impossible by external disinfection to affect bacteria in the tissues. 



GROUP 4. 



Diseases caused by Phycomycetes 



The Phycomycetes are the alga-like fungi, as a rule possessing non-septate 

 vegetative mycelium and developing both sexual and asexual sporeg. In some 

 cases the mycelium is profuse and in others it is reduced to a minimum. Zoos- 

 pores or motile spores are produced in the cases under consideration. 



(a) Black Wart or Potato Canker 



This is one of the most serious and virulent of potato diseases and is now 

 known to occur in England, Scotland, Ireland, Scandinavia, Gejrmany, France. 

 Italy and it has been reported from Africa. It is common in Newfoundland 

 but is practically confined to Pennsylvania on the continent. In Pennsylvania 

 the report by McCubbin showed that in 1920 the disease occured in 781 gar- 

 dens in 53 towns of 9 counties, so that the area involved covers approximately 

 3,000 acres although the actual areas total about 100 acres. 



The disease is known under various descriptive names, such as Cauliflower 

 disease. Black Scab, and Wart disease, but Potato Canker or Potato Wart are 

 more commonl}^ accepted. Schilberszky discovered the disease in Hungary 

 in 1898 and attributed it to Chrysophlydis endobiotica. Percival. in 1910, made 



