696 EXPERIMENT STATION EECORD. 



fjil^_ ,:). — Dislilliitfs iiK-lu(U' all oilsdcrivcil from crude oil l)y distillation. They vary 

 con.'-idenihly in tlu'ir speoiiif ^iravity and their physical ])roi)erties. Emulsions made 

 from California oils have as a rule been less satisfactory than those made from east- 

 ern kerosene, and mechanical mixtures are considered much superior to emulsions. 



The distillates are considered from the standpoint of their insec^ticide value and 

 also with regard to the injury caused by them to leaves and fruits. The vegetable 

 tissues are injured by the penetration of oil into the interior of the plant substance, 

 and this penetration varies in extent and rapidity according to the nund)er of sto- 

 mata and other anatomical structures of the leaves. The chief toxic effects of the oils 

 in the plants are due to diffusion. A drop of oil upon an orange leaf spreads more 

 rapidly and also evaporates more readily than upon an apricot leaf; it therefore 

 causes less injury upon the former than upon the latter. The heavier oils cause more 

 injury than lighter oils, on account of their slow evaporation. Older leaves, on 

 account of their roughness, prevent the drops of oil from spreading and thus become 

 injured to a great extent. Very young leaves may become entirely covered with the 

 film or oil, and thus be killed. The injury from distillates is in the author's opinion 

 not due to any impurities in the oils, but to the oils themselves. 



Notes are given on the effects of mixed oils, general and local injury of these oils, 

 methods of application, and the influences of weather conditions, temperature, etc. 

 The more force used in the application of the oils the greater the amount of penetra- 

 tion. A pronounced humidity of the atmosphere has the effect of opening the sto- 

 mata in the leaves and thus allowing greater penetration of the oil. The injury to 

 plants from oils is due to the prevention of transpiration, exclusion of the air, and to 

 chemical toxic effects. The latter effects are manifested within 00 hours in an atmos- 

 phere containing gasoline, by a general bleaching process. 



The practical bearing of these investigations is discussed by the author. It appears 

 that many species of insects and mites escape the most careful spraj'ing with distil- 

 lates; in fact black scale and other insects survive the severest treatment which trees 

 will stand, in sufficient numbers to reinfest the plant within a short time. An exten- 

 sive reappearance of young scales was noted within from 2 to 3 weeks after spraying. 

 According to the author no applications of distillates can be made without more or 

 less injury to trees and fruit. Both leaves and fruit become spotted and drop. Two 

 applications are all that can be economically applied in 1 year, since experience 

 has shown that if 3 or 4 applications are required, spraying will not be less expen- 

 sive than fumigation. 



Sulphur sprays for red spiders, W. H. Volck {California Sta. Bid. 154, pp- H, 

 figs. 4)- — This bulletin is occupied with an account of experiments in the destruction 

 of a species of Bryobia on almond and other deciduous trees, and a species of Tetrany- 

 ch us on orange. Mites were inclosed in small cells and subjected to the action of 

 sublimed sulphur. All mites thus treated died within a short time, or if they laid 

 eggs the eggs did not hatch. Mite-infested branches were dusted with sublimed sul- 

 phur and inclosed in paper bags without being removed from the tree. The mites 

 were nearly all destroyed within a period of a month. 



During these experiments it was found that the use of ground or sublimed sulphur 

 was effective in destroying mites. The trees may be dusted when wet with dew, but 

 results from the use of the dry method are not always satisfactory. Spraying with 

 a finely divided sulphur mixed with water is recommended. In order to cause the 

 sulphur to adhere for as long a period as possil)le on the leaves experiments were 

 made in mixing flour paste, lime, and other adhesive materials with the spray. The 

 best results were obtained from the admixture of flour paste. Good results were also 

 obtained when adding sulphate of potash to the sulphur spray. During the winter 

 of 1902 about 100 orange trees were sprayed with sulphur and the results were quite 

 satisfactory. The trees and fruit were not injured. Almost equally good results 

 were obtained with sublimed and ground suljihur, but it is recommended that the 

 sulphur should be in a finely divided condition. 



