150 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



veinlets and these veinlets will appear collapsed and brown, to a point 

 where there appears to be a series of punctures probably made by the 

 beaks of the nymphs. 



The more rapid growing varieties of potatoes suffered less than those 

 of slower growth, apparently due to the larger number of leaves pro- 

 duced. Each leafhopper appeared to be able to destroy a leaf. If 

 there were only as many hoppers as leaves, the plant kept on growing ; 

 if on the other hand, there were two hoppers to a leaf, it died. 



The Relation of Hopperburn to Tipburn 



Tipburn has been used for years, to designate any burned condition 

 of the leaves, for which no causal agent could be found, the most com- 

 mon explanation being that it resulted from too rapid transpiration 

 due to abnormal conditions of temperature and moisture, although Dr. 

 L. R. Jones, in first discussing it, suggested that insects might be a 

 factor in its production. It seems probable that a considerable amount 

 of the injury referred to as tipburn, in the past, has been due to the 

 leafhopper. On the other hand, there are, no doubt, other causes of 

 the burning of potato foliage and it will be one of the problems of the 

 future to differentiate these factors. 



At first it was thought that there was a great variation in suscepti- 

 bility of different varieties, but further study appeared to show that 

 the variation was due to the difference in time that the foliage appeared 

 on the potatoes. 



Potatoes that were up at the time that adult leafhoppers were flying 

 in the spring, were injured in about the proportion of their foliage. 

 Potatoes that came up later, even if in adjoining rows, were not injured 

 at all until the adults of the new generation flew to them in July and 

 August, 



In every case the first injury appeared on the older leaves, below the 

 top. This was due to the fact that between the time the eggs were laid 

 and the young nymphs had hatched and had time to produce the 

 injury, new leaves would have grown above the injured ones. 



Cage Experiments 



A cage was put over a medium-sized potato, early in August, and be- 

 tween 200 and 300 leafhoppers added. In three days all of the upper 

 leaves of the plant were rolled up and burned brown and the growth of 

 the plant stopped. Following this, two cages were placed over potato 

 plants of equal size. Another plant of similar size was selected as a 

 field check. These plants were scarcely two-thirds of the height of the 

 cages and were considerably burned on the lower half when caged. 



In one cage, between 200 and 300 leafhoppers swept from the field 



