I 
218 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 13 
ilar cooperative agreement, in spite of the fact that for the coming 
season the college is able to pay only fifty, instead of one hundred 
dollars a month towards the salary of the field assistant. 
President W. C. O’Kane: We will now take up the paper by 
Mr. E. D. Ball and F. A. Fenton. 
WHAT PER CENT OF TIPBURN IS CAUSED BY THE 
POTATO LEAFHOPPER? 
By E. D. Ball and F. A. Fenton 
The senior author in 1919 1 pointed out that the potato leafhopper 
was responsible for a considerable part of the injury to potatoes which 
had previously been called tipburn, and suggested the name “ hopper- 
burn” for this specific effect. The authors of this article in their 
season’s work in Iowa this year attempted to ascertain what was the 
relative proportion of the different factors in causing tipburn. Accord¬ 
ingly a number of fields of potatoes at Ames were kept under continu¬ 
ous observation during the entire season. The number of leafhoppers 
was recorded from day to day, as well as the relative percentage of 
nymphs and adults and their position on the vines. 
It was found that there was no evidence of tipburn in the fields until 
after the over-wintering leafhoppers had appeared, laid eggs, and the 
generation of nymphs had begun to develop in numbers. The mar¬ 
ginal burning then began to appear on the older leaves of the plant and 
extended observations in different fields showed that the amount of 
the burning was proportional to the number of leafhoppers present 
on the particular leaves affected, that in no case did burning develop 
in fields where no leafhoppers had appeared or on plants on which 
there were no leafhoppers, nor on the upper parts of the fast growing 
plants. The burning first appeared on the leaves at some distance 
from the top and gradually progressed upward as the plant developed 
and in about the same ratio as its growth for a considerable time. 
This was found to be correlated with the time required for the eggs 
deposited in the young shoots to incubate and the young nymphs to 
develop to an effective size. It was further found that as the burning 
progressed to the point where the plant was weakened and growth 
stunted, that it gradually approached the top until finally, at about the 
time growth ceased, the entire plant was affected and soon succumbed. 
Careful counts were kept on a number of plants and each young 
nymph removed as soon as it hatched. In this way the average num- 
1 Jour. Econ. Ent. Vol. 12, p. 149, 1919, and Report of the Division of Ento¬ 
mology, Wisconsin Department of Agric. for 1917-19; p. 76, 1919. 
