Changes in California Red Scale Populations Following Sprays of Oils With and Without Derris Resins

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Abstract
California red scale populations were studied after spraying with heavy medium, and light medium oils alone and with added derris resins. Contrary to expectations light medium oil did not have less residual action against crawlers and thus the anticipated build up of infestations did not follow. Confirming previous work, by these authors it is reported that the minimum conc. of rotenone in oil required for a satisfactory control is about 0.1% plus other extractives of derris root. In 5 groves treated with light, medium and heavy medium oils final infestation was more than twice as heavy in plots treated with oil alone as where proper concs. of derris resins were used. A medium light oil showed more residual action than an extra light oil. In general, the relative rate of population increase was. greater the smaller the number of insects surviving the sprays. Most benefits from the use of derris resins are obtained when conditions favor red scale increase.

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