October 



SCIENTIFIC AGRICULTURE 



55 



Diseases of the Potato 



IW B. T. D1CK«0X, 

 Fiofessor of Botany, Macdonald College. 



Introduction. 



The potato crop i« of prime inipoitauce 

 to Canada and therefore the importance of 

 <i knowledge of the diseases of the potato 

 need not be stressed here — it should be 

 taken for granted. Without quoting sta- 

 tistics, the losses from potato diseases 

 amount to millions of dollars every year. 

 This means that every year a percentage of 

 the seed planted is useless, that a part of 

 every acreage is -wasted, that labor is not 

 used to full advantage and, finally, that the 

 grower suffers a direct financial loss whe- 

 ther he is growing potatoes for sale or use. 



In dealing with this series the diseases 

 will be considered in the order now given. 



1. — Diseases in which insects are the 

 agents of infection or in Avhich insects are 

 the direct cause. 



These are : — 



(a) Hopperburn (or tip burn). 



(b) Mosaic and mosaic dwarf. 



(c) Leaf roll. 



2. — Disease caused by a myxomycete ■.-^— 

 (a) Powdery scab {Spongospora Sub- 

 terranea. ) 



3. — Disease caused by bacteria : — 



(a) Black leg {Bacillus atrosepticus.) 



4. — Diseases caused by Phycomycetes : — 



(a) Black wart or potato canker 

 ( Ch rysoph lid is endohiotica. ) 



(b) Leak {Pythium de Baryanum) . 



(c) Late blight {Phytophthora infes- 

 tans). 



o. — Disease caused by an Ascomycete : — 



(a) Wilt and stem-rot (Scleroti}ii(i 



lihertiana.) 



6. — Disease caused by a Basidiomycete : 



(a) Dry stem-rot and black scurf 



{Corticium vagum var. Solani.) 



7. — Diseases caused by Fungi imperfecti : 



(a) Early blight {Alternaria solani). 



(b) Wilt (Fusarium oxysporum). 



(c) Common scab {Actinomyces sca- 

 bies.) 



(d) Skin spot {Oospora pnstulaus). 



(ej Silver scurf iiSpoiigylocladiiiin 



atrouirens.) 

 { f ) Dry rot of tuhevn XFusariutn spp ) . 

 (g) Net necrosis {Fusarium spp.) 

 8. — Diseases caused l)y conditions which 

 adversely modify the normal physioh)gical 

 ])rocesses : — 



(a) Black heart. 



(b) Frost necro.sis. 



(c) Net necrosis. 



(d) Spindling sprout. 



(e) Hollow heart. 



(f) Arsenical injury. 



It Avill tlius be seen that there are some 

 twenty or more common potato diseases 

 \\ith wjiicli the grower may have to con- 

 tend at different seasons. 

 GROUP 1. 



In this group are placed tliree (or four) 

 diseases in wliich in.sect8 play an important 

 role. 



(a) Hopperburn, or tipburn as it used 

 to be called, occurs periodically whenever 

 dry conditions prevail in potato growing 

 areas. It was noted first in Iowa in 1876 

 by Osboi-n, but wilting of early varieties 

 was the most pronounced characteristic. 

 Osborn recorded the presence on such dis- 

 eased plants of Empoasca Mali (Le Baron) 

 knoAvn as the leafhopper. In 1908 its 

 work was observed in New York, and again 

 in 1909. Fraser reported it from Quebec 

 in 1913, it was again serious in Iowa in 

 1915. and in Vermont in 1917. Ball in 

 Wisconsin in 1918 studied the disease which 

 that year extended from Montana and 

 Kansas to New York and New Jersey. This 

 year the leafhopper has been very preva- 

 lent in Quebec and hopperburn is certain 

 to cause considerable loss. 



Symptoms of the Disease. 



The first signs of the hopperburn usual- 

 ly appear during the latter part of July 

 or early in August with most severe effects 

 from the middle of August to the middle 

 of September. On some of the lower leaves 

 a slight yellowing begins at the tip or edge 



