THE ALFALFA CATEKPILLAB. 37 
a few even renovate oftener. Mr. Stroven, of Holtville, Cal., reno- 
vates just as often as it is possible for him to do so, and in 1911 this 
was four times. Leaving the matter of insects entirely out of con- 
sideration, enough benefit is derived from renovation to pay many 
times for the cost of the work. If a disk harrow is used, it should not 
be set at an angle, as this would be likely to cause injury to the crowns, 
but should be run straight and forced into the ground by weights. 
DIRECT METHODS OF CONTROL. 
INSECTICIDES. 
In dealing with insect pests affecting cereal and forage crops it 
has proved possible in only a few instances to control them by the 
use of any of the various insecticides or poisons. The reason for this 
lack of success lies largely in the fact that such crops are distributed 
over a wide area, and the expense of application of any insecticide as a 
control measure is necessarily high, while a lack of thoroughness is 
likely to arise when one tries to keep the expense of treatment down 
to an economical basis. 
Since the alfalfa hay is fed to stock, it is not possible to use any of 
the arsenical poisons against the caterpillar of the alfalfa butterfly. 
A few experiments, however, were tried with pyrethrum, or " buhach." 
As this is not a poison, and since its fatal effect upon the larva? of 
butterflies is produced externally through their breathing pores, 
there would be no danger to stock. Pyrethrum was used in one case 
in 1910 in full strength, and in another instance it was diluted with 
equal proportions of flour. An application was made by dusting this 
substance from a cheesecloth sack, following the primitive method 
of applying Paris green to potato vines, at the rate of 3 pounds of 
pyrethrum to the half acre, which in the case of diluted material 
would make 1J pounds of pyrethrum to the half acre. This first 
test was made on July 8, 1910, and no results were obtained, because 
of the fact that just two days later practically all of the worms in 
the field where the test was being made were destroyed by the malady 
before mentioned. The same experiment was repeated, however, 
on September 22, and in this case the results were negative, not a 
caterpillar being killed. It would seem, therefore, that the applica- 
tion was not sufficiently heavy to kill the worms, and that to haA^e 
increased the amount of pyrethrum applied might have resulted in 
the eradication of the pest; but as the cost of pyrethrum at the rate 
of 3 pounds to the acre is already nearly $2, without considering the 
expense of application by hand, this could not be considered from 
an economic point of view. 
In 1913 some additional experiments were tried with the same 
material by Mr. T. Scott Wilson at Tempe, by using it full strength. 
This killed about 50 per cent of the larva?, but the cost of application 
