POTATO LEAF-ROLL. 1 



By W. A. Orton, Pathologist in Charge of Cotton and Truck Disease and Sugar-Plant 



Investigations. 



INTRODUCTION. 



The years 1911 and 1912 have been marked by the prevalence of 

 potato troubles in some of our Western States more serious than any 

 hitherto experienced. Such heavy losses have resulted, particularly 

 in eastern Colorado and western Nebraska, that the production of 

 potatoes, generally one of the most profitable crops for these irrigated 

 districts, has been rendered so uncertain that the growers have been 

 compelled to greatly curtail their acreage. 



The Bureau of Plant Industry has nearly ready for publication a 

 bulletin on these new diseases, but as this will necessarily be some- 

 what technical in character and not available for distribution until 

 later in the season, this paper is issued for the information of the 

 potato growers in the districts affected. 



The identification of the disease responsible for the decrease in 

 potato production in the country east of the Rocky Mountains and 

 west of the one hundredth meridian has been in doubt until recently. 

 It was at first thought to be an aggravated form of diseases already 

 known, Rhizoctonia, stem-blight, and Fusarium wilt, but it is now 

 considered a new and distinct malady called "leaf- roll." This has 

 been common in Europe since 1905, but has not hitherto been iden- 

 tified in the United States. 



DESCRIPTION OF LEAF-ROLL. 



As indicated by the name, leaf-roll is marked by an upward rolling 

 of the leaves on then- midrib. There is usually a pronounced change 

 in the color of the foliage to a yellow, unhealthy shade, often tinged 

 reddish or purplish. 



The disease may start early in summer and be far advanced by 

 the end of July. The plants do not die quickly, as they do when 

 attacked by Fusarium wilt, but may live nearly as long as healthy 

 oil es. The growth is checked and the formation of tubers prevented. 

 Often no potatoes are set, or only small ones clustered around the 



i Issued Jan. 4, 1913. 

 [Cir. 109] 7 



