THE ALFALFA CATERPILLAR. 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 larvae 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 I§ 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 have 

 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 



