10 HOW TO CONTROL THE PEAR THEIPS. 



contain too much of the light gaseous oils, which lower the flashing 

 point. 



There are several commercial preparations of oil emulsions and 

 miscible oils on the market, but these have not given as satisfactory 

 results against the adult thrips as the homemade preparation, espe- 

 cially on pears, on account of the noticeable lack of penetration into 

 the cluster buds. Besides, all of these commercial preparations are 

 far more expensive. Allowing 25 cents per hour for labor in making 

 the soap and the concentrated homemade emulsion, the commercial 

 preparations cost the grower from 2 to 5 times more than the more 

 efficient homemade preparation. 



COMMERCIAL RESULTS. 



During the season of 1909-10 many large-scale experiments and 

 demonstrations were carried out in pear, prune, and cherry orchards 

 to determine more conclusiveh' the effectiveness of this combined 

 spray and to put the treatment on a commercial basis; also, that 

 growers might see for themselves the results of the work and know 

 the monetary gain possible by such control measures as are recom- 

 mended. The commercial results from some of these experiments 

 are given below: 



PRUNES, SANTA CLARA COUNTY. 



The 16-acre prune orchard belonging to Mr. P. Landon, situated 

 in the Willows district, near San Jose, Cal., consists of some of the 

 largest and finest prune trees in the valley. The trees, which are 

 about 25 years old, are planted 20 feet apart and the branches now 

 overlap between the rows. The orchard has very heavy sandy loam 

 and has been well cultivated and usually irrigated twice each year. 

 Thrips became injurious in the year 1906, increasing greatly in 1907, 

 and causing much injury over the entire orchard, so that instead of a 

 normal crop of a hundred or more tons of gre^^n (undried) prunes the 

 entire 16 acres produced only 18 tons of green fruit. Injury by the 

 thrips was worse in 1908, the yield that year being only 10 tons of 

 green prunes. 



Demonstration for 1909. 



In the fall of 1908, under direction of the Bureau of Entomology, 

 Mr. Landon plowed and cross plowed this orchard to a depth of 9 

 inches, with thorough harrowing after each plowing. Thrips were 

 very abundant in the soil, there being sometimes as many as 3,000 

 to the square foot. 



The following table, giving the emergence of adults in spring from 

 samples of soil taken before and after plowing, shows that approxi- 

 mately 70 per cent of the tlirips were killed by cultivation : 



