KATYDIDS INJURIOUS TO ORANGES IN" CALIFORNIA. 



21 



Preliminary Tests with Arsenicals. 



Four groups of 10 Washington navel trees each were sprayed on 

 April 15, 1912, for the purpose of determining the maximum strength 

 of the different arsenicals that could be used with safety to the trees 

 and to compare the adhesive qualities of the insecticides. The 

 spraying was done in bright, warm weather and the trees were thor- 

 oughly drenched. The test trees were examined on April 19, and 

 although covered with tender, new leaves not the slightest trace of 

 burning resulted. Subsequent examinations in no case revealed 

 burning or damage resulting from the spray application. It was 

 later found safe to use considerably stronger solutions of the arseni- 

 cals, the maximum strengths of which were (1) arsenite of zinc, 2 

 pounds (powdered) per 100 gallons of water, and (2) arsenate of lead, 

 8 pounds (dry) per 100 gallons of water. The distribution of the 

 arsenicals over the leaf surface after the spray dried did not seem 

 entirely satisfactory, especially on the young leaves, whose waxy sur- 

 face had caused the water to gather in drops, leaving the poison in 

 spots. The addition of lime-sulphur solution to the arsenical sprays 

 and the regulation of the nozzles so as to deliver a moderately fine 

 spray remedied this objection. 



Plan of Experiments. 



The principal spraying experiments conducted against the katy- 

 dids are outlined in Table II. Each of the sprayed plats consisted of 

 two rows of 33 trees each, or 66 trees to the plat. Three pairs of 

 rows of trees extending through the midst of the sprayed area and 

 the trees adjoining the sprayed area on the west were left unsprayed 

 as checks. (See experimental orchard, PI. V, fig. 2.) 



Table II. — Plan of spraying experiments against citrus katydids, Lindsay, Cal., 1912. 



No. of 

 plat. 



Insecticides in gallons and 

 pounds per 100 gallons of 

 water. 



Lime- 

 Bulphur 



Mill inn. 



Arsenite 

 of zinc. 



Arsenate 

 of lead. 



1 



2 

 3 

 1 



S 

 6 

 7 

 8 

 8 



OalUms. 



■1 



2 

 2 

 2 

 2 



Pounds. 

 2 

 3 



! 



Pounds. 







4 



c< 



s 







2 









1 







