THE CITRUS THRIPS. 31 
NURSERY-SPRAYING EXPERIMENTS. 
Plat No. 1. 2,550 Valencia and Joppa orange trees, sprayed with lime-sulphur, 
1-50. 
2. Several thousand Washington navel orange trees, sprayed with 
lime-sulphur, 1-75, and tobacco extract (2f per cent nicotine 
sulphate), 1-150. 
Time and number of applications. — Three applications of the in- 
secticides were made at the valley ranch, Series I, with the object of 
saving the fruit from injury. Owing to a very cold and backward 
season and the age of the trees, growth was scant and the first appli- 
cation was not necessary until June 2. The second application was 
timed principally to catch adult thrips which had transferred to the 
fruit and larvae which had issued from it since the first application 
and was started June 17. The third application was timed solely by 
the abundance of thrips on the fruit and was begun July 8. 
The first application at the foothills ranch, Series II, was started 
May 15, and the second June 6, both about a week later than was 
intended, owing to failure of the ranch foreman to produce sprayer, 
teams, and labor promptly when requested, the writer being depend- 
ent upon the grower for these items by agreement. The difference in 
the time of the first application between the valley ranch, Series I, 
and the foothills ranch, Series II, indicates approximately the differ- 
ence between the two localities in the time when the petals dropped 
and the thrips began to feed on the fruit. 
The nursery trees were sprayed June 7, July 15, and August 31; 
the sprayings were timed solely by the abundance of thrips. 
RESULTS FROM SPRAYING. 
The determination of the relative value of the different insecticides 
and of spraying is based solely upon the effectiveness of the work 
in raising the commercial grade of the fruit. These grades repre- 
sent money values, and their improvement, which was the primary 
object of the investigation, thus effects a tangible saving. The 
qualities determining the grading of oranges were studied out at the 
various packing houses, and in this work the writer received the 
willing cooperation of the managers of most of the packing houses 
at Lindsay, Cal. As the fruit from the experiments of Series I was 
graded under a different system from that of Series II, it will be 
necessary to state the results of each series of experiments in terms 
of the commercial grading of the fruit from that series. 
RESULTS IN SERIES I. 
The results of the spraying experiments at the valley ranch are 
summarized in Tables VII and VIII. The comparatively slight in- 
festation in this orchard in 1911 is evident from the figures for the 
unsprayed plats, Nos. 1, 4, 7, 13, and 22, in Table VII. The varia- 
tion in the percentage of fruit injured sufficiently to reduce the grade 
