Potato SPRAYING IN MINNESOTA 29 
together with results in the laboratory, they throw some light on the 
problem of leaf hopper control. The results may be tabulated as fol- 
iows: The numbers in the per cent killed column represent a com- 
parison of the number of hoppers on the sprayed plots with the 
number on check plots. An estimate of the average number of hoppers 
per plant was made by counting those on one plant in each thirty feet 
of each row and averaging for the plot. 
TABLE III 
Per cent killed 
ee Nicotmmesn|=500eancdissoape lilbys topo Omcalaa- meer: 65 
Zee NiConimmen ol -o00mawithotiiesOapmec cect cece ac 17 
Sh Niece OlOAwS IWe500) Gooucuonooseoocsccuusacgoends 3 
AL Nii@oimne Glen ISSU0) Sktucoomoboccooooccsosbe dbo: 4 
5.) Black leat 407 1-500 and soap 1 Ib: to 50 gal... 2... 13 
Gung blacksleared (ml 5 00 nwathoutssOapeecde meee n eee 6 
From the above table it is evident that nicofume with soap was 
the only material giving even partially satisfactory control in the field. 
Since those results were not sufficiently clear cut to form a safe basis 
for any conclusions, it was deemed advisable to test the same materials 
under carefully controlled laboratory conditions to determine their 
comparative toxicity to leaf hoppers. On account of the difficulty of 
handling the adults, well developed nymphs were used. Leaves, each 
with six or more hoppers, were placed in individual vials closed with 
cheese cloth. As soon as possible after collection, each leaf was re- 
moved from the vial with the leaf hoppers clinging to it, quickly sprayed 
with the desired material, and placed in a small cheesecloth cage. A 
few leaf hoppers were, of course, lost in this operation, but enough 
remained for the purpose of the experiment. The spray dried from the 
leaves very quickly in the cheesecloth cages thus imitating outdoor 
conditions as nearly as possible. The morning following treatment 
the cages were opened and the results of the spraying were recorded. 
As a check, leaf hoppers were sprayed with clear water and placed 
in cheesecloth cages. Without exception, 100 per cent survived this 
water treatment. The nicotine compounds were all used at the rate 
of one part to 500 parts of water. In order to determine the influence 
of the kind of water used in mixing the spray materials upon the 
effectiveness of the spray, each material was used with distilled water, 
water from Parker’s Lake, and tap water. The results may be 
tabulated as follows: 
