1920.] 



Potato Leaf-curl. 



287 



POTATO LEAF-CURL. 



A LARGE amount of careful research work has been carried 

 out during the past few years on Potato Peaf-curl, especially 

 in Holland, but also in Canada, Bermuda and the United 

 States. The results obtamed, particularly with regard to the 

 early phases and possibly infectious nature of the disease, 

 are of importance to all potato growers, and especially to those 

 who grow for seed. Though the last edition of the leaflet on 

 Potato Leaf- curl (Xo. 164) was only issued by the Ministry in 

 19 18, it has been re- written in order that the new results may 

 be incorporated, and in view of the importance of the subject 

 the information it contains should be widely known. The 

 following is the text of the revised leaflet : — 



Probably no disease is more responsible than leaf- curl for the 

 weakly potato plants and light crops so often seen, especially 

 in gardens and allotments. In the lighter soils in the southern 

 and drier parts of the country it is very prevalent, and is 

 particularly abundant where the practice of using home-saved 

 seed is followed. There is no doubt that, if its presence were 

 eliminated, an increased yield of several tons per acre would 

 be obtained. 



The term " ciirl " as applied to a malady of the potato has 

 been in use in England for more than two centuries, but it is 

 clear that the older writers included under this name more 

 than one disease. In the present article the name leaf -curl 

 is applied to the disease now generally associated with the 

 deterioration in yield of potatoes, particularly when grown in 

 southern districts, to account for which no fungus parasite has 

 been discovered. It is applied to that form of disease which 

 on the Continent (where it is often very severe) has been 

 called leaf-roll. The designation leaf-roll has also been 

 used occasionally in this country, and is at present used in 

 America. But as the name leaf- curl is weh established 

 throughout Britain, and is of long standing, there appears to 

 be no necessity for changing it. 



Description of Affected Plants. — The most marked symptom 

 of potato leaf- curl is the curling or rolling inwards of the 

 margins of the leaves {sec Fig. i). In mild attacks this 

 rolling is confined to the lower leaves. The curled leaves are 

 thicker and more crisp than in normal plants and give almost 

 a rattle when knocked together. They are usually pale in 

 colour and often die prematurely from the tips backwards. 

 In bad cases the middle and upper leaves are also curled 

 (see Fig. 2) and in certain varieties such as President, 

 ^lidlothian Early and Lochar the whole plant is dwarfed. 



