CONTROL OF THE HOP APHIS. 27 
> Nicotine sulphate, 1-3,000 and 1-3,500, in combination with 
whale-oil soap or flour paste has been successfully used in experi- 
ments, but it would be safer in practice to use the lower dilutions. 
In case the greater dilutions are used, careful observations should be 
maintained to be sure that the spray is doing effective work. The 
nicotine preparations which come in cans have a slight tendency to 
settle. In case they do settle and are not thoroughly mixed before 
measuring, the percentage of active insecticide used in one lot of 
spray may be enough less than should be present in a uniform portion 
to render the spray ineffective. It is advisable, therefore, to be sure 
that these preparations are thoroughly mixed before measuring. 
MIXING NICOTINE SOLUTIONS AND WHALE-OIL SOAP. 
During certain spraying experiments with tobacco extracts and 
whale-oil soap some difficulty was experienced in mixing the concen- 
trated solutions of blackleaf tobacco and whale-oil soap. When 
these were combined a greenish-gray precipitate of a flocculent nature 
was formed. A similar precipitate occurred when one of the mate- 
rials was diluted and the other left concentrated. When each solu- 
tion was diluted to half of the final amount, however, this objec- 
tionable nozzle-clogging precipitate did not appear. 
Flour paste does not have this effect, but when whale-oil soap is 
used as a spreader for tobacco sprays, both solutions must be well 
diluted before mixing. 
PREPARATION OF THE FLOUR PASTE. 
In preparing the flour paste, mix a cheap grade of wheat flour 
with cold water, making a thin batter without lumps, or wash the 
flour through a wire screen with a stream of cold water. Dilute until 
there is 1 pound of flour in each gallon of mixture. Cook until a 
paste is formed, stirring constantly to prevent caking or burning. 
(See PI. VI, fig. 1.) Add sufficient water to make up for evaporation. 
If the paste is not sufficiently cooked, the resulting spray will not 
be effective. If overcooked^ the paste will harden when thoroughly 
cool; it will then not mix with water very readily. Usually, how- 
ever, the paste is used as it is prepared, and overcooking is not a 
disadvantage. 
When mixed in a spray tank flour paste has a tendency to settle, 
and in order to do satisfactory work agitation is necessary. This is 
only a slight disadvantage, however, and is necessary with most spray 
materials. The large spray tanks are usually fitted with an agitator, 
and a hoe makes an effective agitator for the 50-gallon barrels, so that 
this problem is a simple one. 
