EXPERIMENT STATION A\'ORK WITH INSECTICIDES. 251 



than when placed on one surface only, but when the oil was sprayed 

 on the underside of the leaves the etfect was about as harmful as 

 when both surfaces were covered. At the California Station the 

 injuries resuhin<2; from distillates wei-e appai-ently not due to im- 

 purities in the oils, but to the use of too heavy oils. A hi^jh-firade 

 eastern kerosene pive fjood results, whiU' cheap western kei'osenes 

 were unsatisfactory. It was also found jxjssibk^ to reduce the (kin<i;er 

 froni heavy oils by mixing them with kerosene. The burninij ell'ect 

 in small spots observed on oranges and leaves after spraying from oils 

 was apparently due to the fact that the oil when mixed with water 

 does not spray evenly over the surface of the leaf, but collects in 

 dro|)s of greater or less size, from which the injury results. If tlie 

 humidity of the air is very high at the time of spraying, the stonuita 

 of tlie leaves are o^hmi and may lead to considerable ])enetration of the 

 oil. It is not advisable, however, to spray when the leaves are in a 

 condition of extreme dryness. The best time for the use of oils 

 appears to be in weather during which the air is moist. Distillate 

 oils appear to have less injurious eli'ects when the temperature is 

 relatively high. In order to avoid as far as possible the injury from 

 distillates the California Station reconnnends that the oils be sprayed 

 as nearly as possible straight downward, in order not to cover the 

 under surfaces of the leaves. 



At the Connecticut State Station " it was found that spraying trees 

 just before the leaves appeared in the s})ring witli crude oil or with a 

 mechanical mixture of kerosene and water containing '20 per cent of 

 kerosene gave the best results in the control of the San Jose scale on 

 large orchard trees. The kerosene used at this station was claimed to 

 have a fire test of 150°, and the crude oil showed a specific gravity of 

 43° liaume. No harm was produced by the use of crude oil or kero- 

 sene and water containing 15 to 20 pei- cent of oil when applied to 

 dormant trees in early spring. Mechanical mixtures of refin(Hl or 

 crude oils containing 10 to 30 per cent of the oil were used on i)each 

 trees in foliage. It was found that the San Jose scale could be kept 

 in check by this method, and no harm was done to the peach trees as 

 long as the ([uantity of oil was not above 15 per cent. 



In Idaho '^ crude petroleum obtained from San Francisco was used 

 in experiments in the destruction of San Jose scale. The crude 

 petroleum was used in emulsions containing from 5 to 50 per cent. 

 No harm was done to pear trees from spraying with undiluted jietro- 

 leuni, while an ap|)le tree was killed. A 50 per cent enndsion of 

 crude petroleum did no damage to either pear or apple trees. \u 

 emulsion containing 33 per cent of crude oil was applied to apjjle 



« roimectiout State Sta. lUils. 1.35, 130. 

 6 I(lii!i(» Stii. liul. 20. 



