256 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



DOES BORDEAUX MIXTURE REPEL THE POTATO 

 LEAFHOPPER? 



By Charles L. Fluke, Jr., University of Wisconsin 



At various times in the past the attention of our entomologists has 

 been called to serious outbreaks of the potato leafhopper and for many- 

 years a more or less serious trouble has occurred on potatoes known as 

 tip burn. A serious outbreak of the latter trouble appeared through- 

 out a part of the country in 1918. This trouble happened in Wisconsin 

 to such an extent as to decrease the potato crop at least 25 per cent. 

 The potato leafhopper was also extremely abundant and observations 

 have shown that the burning was always worse in the presence of a 

 notable number of leafhoppers. It then became easy to associate the 

 tip burn injury of this year with the leafhoppers and many observa- 

 tions were made in this connection. While carrying on experiments 

 with Bordeaux mixture in combination with certain arsenicals for the 

 control of the potato beetle, it was noticed that the plants sprayed 

 with Bordeaux mixture were abnormally free from tip burn. Observa- 

 tions made at the time also showed that the leafhoppers were not abun- 

 dant on these plants. Thirty plots in all were used in a series to test 

 out various insecticides on Early Triumphs and Rural New Yorkers. 



The first application of spray was put on July 10 at which time the 

 plants were in good condition to show the effect of the insecticides. 

 No curling or darkening of the leaves was apparent at this time, and 

 it happened that only one plot of Early Triumphs received a Bordeaux 

 combination spray. The other plots on which Bordeaux combinations 

 were used were late potatoes. Daily observations were carried on to 

 note the effect of these sprays on the foliage. Three days afterward 

 (July 13) a peculiar darkening, not a drying, of the edges and tips of 

 the leaves of the early potatoes was noticed on some of the plots which 

 at first appeared to be due to the action of the spray until it was noticed 

 that this also occurred on the check plots. At the same time consider- 

 able curling of the leaves was also observed. A few days later the 

 characteristic burning of the leaves appeared on most of the Triumph 

 plots. The only one which showed very little of the browning was one 

 plot of four rows sprayed with zinc arsenite plus Bordeaux mixture 

 4-4-50. On July 23 a careful examination of the vines revealed the 

 fact that the leafhoppers were extremely numerous wherever the tip 

 burn was evident. On the above mentioned Bordeaux zinc plot the 

 number of hoppers was comparatively smaller. It was plainly evident 

 that the leafhoppers were very likely the cause of the tip burning and 

 also that Bordeaux mixture had some repellent effect upon the hoppers. 

 The counts were made on July 31 and August 1. The leafhoppers were 

 more abundant on the sprayed plants in the rows next to those 



