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 or 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, PL 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- 
sulphur 
solution. 
Arsenite 
of zinc. 
Arsenate 
of lead. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
Gallons. 
2 
2 
2 
2 
2 
2 
Pounds. 
2 
3 
4 
Pounds. 
4 
6 
8 
2 
3 
4 
