HOW TO CONTROL THE PEAR THRIPS. 7 



but all of them have proved to be absolutely of no avail, or at most 

 impractical and expensive. In most cases the general vigor and 

 health of the trees were improved by early fall irrigation and by the 

 application of fertilizers. 



CULTIVATION. 



Thorough plowing in the fall in i)rune orchards planted on gravelly 

 and sandy soils gave very helpful results. Success by deep plowing, 

 cross plowing, and harrowing in October and November was fairly gen- 

 eral in all experiments tried in Santa Clara County in the fall of 1908 

 and 1909. This manner of cultivation, when carried out to a depth 

 of from 7 to 9 inches, resulted in killing from 60 to 80 per cent of the 

 thrips present in the soil, but was not a sufficient control, as enough 

 thrips escaped to cause great injury to the buds the following spring. 



SPRAYING. 



A long list of insecticides was tried out in spraying experiments, 

 both in the laboratory and by spraying the trees in the spring. All 

 poison sprays had to be abandoned because of the inabihty to poison 

 the thrips, as both adults and larvae do not feed in a way to be sub- 

 ject to poisoning. Sticky sprays were difficult to apply and proved 

 ineffective, as they do not retain this quality long and the thrips 

 seem capable of moving around on almost any kind of surface. Dust 

 sprays and preventive sprays had to be abandoned because the dust 

 sprays failed to kill and the rapid swelling of buds and continued 

 appearance of new surface area gave the thrips plenty of feeding 

 ground and exposed places of entrance into the buds. Success with 

 contact sprays seemed more apparent; of these, various caustic 

 sprays, such as caustic-soda and carbolic-acid solutions, gave excel- 

 lent results in killing the thrips, but were, as a rule, unsafe because 

 of injury to the trees. 



Solutions of tobacco extract were very promising, and when used 

 at sufficient strengths killed all the thrips actually reached, but they 

 lacked sufficient penetrating quahty to enter the swelling buds, a con- 

 dition absolutely necessary, especially on pears, as most of the injury 

 is done inside the cluster buds. Mechanical mixtures of various 

 mineral oils and animal-oil soaps were tried and abandoned because 

 of the difficulty of keeping them thoroughly mixed and the resulting 

 injury to the trees caused by free oil separating out. Fish-oil soap 

 emulsions \\dth these various oils gave better results, the raw distil- 

 lates running from 30° to 40° Baume being decidedly preferable over 

 either the kerosenes or the heavy crude oils. 



A distillate-oil emulsion made according to directions (see pages 



8-10) gave better penetration into the swelling pear buds than any other 



material which has been tried. There was one drawback, however; 



when this emulsion was used in sufficient strengths to kill all the 



67859°— Cir. 131—11 2 



