April, '19] BALL: THE POTATO LEAFHOPPER 149 



THE POTATO LEAFHOPPER AND ITS RELATION TO THE 



HOPPERBURN 



By E. D. Ball, Ames, Iowa 



The leaves of the potatoes were badly burned during the season of 

 1918 all over the whole northern part of the United States, from Mon- 

 tana to New York, and New Jersey south to Kansas and Ohio. In 

 different places it was called ''blight, tipburn, or aphis work." The 

 writer's attention was called to it on July 17. At this time the early 

 potatoes in southern Wisconsin were largely dying or dead from the 

 trouble. On examining the injured plants it was found that the leaves 

 with only the margins burned invariably had nymphs or cast skins of 

 the potato leaf hopper (Empoasca mali LeB.) on the under sides. Upon 

 investigation, it was found that even the leaves that had been burned 

 entirely brown still had the cast skins of the leafhoppers in numbers, 

 showing conclusively, that the insects had been present on them for 

 some time. Egg scars were also found on all burned leaves at this 

 time. Oftentimes it was possible to find a leaf with a single egg scar, 

 the five cast skins of the different stages of the nymph and the freshly 

 hatched leafhopper, showing that the whole life up to that date had 

 been passed upon the single leaf. The uninjured leaves were also 

 examined, but no egg scars, cast skins, or nymphs were found on them. 

 The adults were just beginning to fly and occasionally a fresh adult, 

 apparently a new arrival, would be found on an uninjured leaf. 



Description of the Injury (Hopperburn) 



The injury varies somewhat with different varieties and different 

 conditions of temperature and moisture, but in general, the first sign 

 is a triangular burned area at the top of the leaf, followed bj' progressive 

 appearance of burned areas, more or less triangular, along the margin. 

 These areas coalesce as the burning progresses, until the entire margin 

 of the leaf is brown and more or less curled up. The l)urned margin 

 increases in width, until only a narrow strip along the midrib remains. 

 In the worst cases, this strip and the midrib binn, the leaf dies, and 

 later the plant succumbs, standing burned and dry. 



On examining carefully the burned leaves, egg scars will be found in 

 the midribs and leaf stems, as shown in 2, 3, and 4 of figure 7. 

 Often t he l)urned triangle at the tip will be found to extend IkicIc nearly 

 to a place where one or more egg scars have so distorted the midrib 

 that it has collapsed beyond that point. The burned areas along the 

 margin will often be found to extend in some distance on the lateral 



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