THE CITRUS THEIPS. 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 (2| 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 larvaa 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. 



EESULTS 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 

 unsprayecl plats, ISos. 1, 4, 7, 13, and 22, in Table VII. The varia- 

 tion in the percentage of fruit injured sufficiently to reduce the grade 



