INSECTICIDES 45 



churn with a force pump by pumping back and forth for five to 

 ten minutes until the oil is thoroughly emulsified, forming a 

 creamy mass with no drops of free oil visible. This stock solution 

 is now diluted so that the resulting mixture will contain the de- 

 sired per cent of kerosene. Thus for aphids one part of the stock 

 solution should be diluted with from 10 to 15 parts of water, giving 

 from 4 to 6 per cent of kerosene in the spray, while for a winter 

 wash for San Jos scale, it should be diluted only three or four 

 times, giving from 16 to 22 per cent kerosene. The emulsion must 

 be thoroughly churned and should be applied with a nozzle throw- 

 ing a fine spray. Apply only enough to wet the insects. Equally 

 effective emulsions may be made from crude petroleum, the pro- 

 portion of the soap and crude oil in the stock emulsion varying 

 with the quality of the oil. Emulsions made with some of the 

 crude oils seem to be much less injurious to foliage of some plants 

 than when made with kerosene. Such an emulsion is made in 

 California from distillate oils and is known as distillate emulsion. 

 We have used crude Texas oils with equal success. 



2. Kerosene. Pure kerosene should never be used on foliage, for 

 though occasionally someone will report using it successfully 

 without injury, in practically all cases serious burning ot the foliage 

 results. It was formerly recommended against the San Jose' 

 scale on fruit trees, but such serious injury resulted that it has been 

 almost entirely discarded, though it may be used on apple and pear 

 trees if applied with a nozzle which throws a fine spray, on a bright 

 sunny day, and only a very thin film applied to the tree while it is 

 dormant, but even these trees are often injured if the application 

 is not made with the greatest care. 



3. Crude Petroleum. Crude petroleum is used in the same man- 

 ner as kerosene against scale insects, but seems to be less injurious 

 to the tree, and has been extensively used in New Jersey against 

 the scale on peaches, where but little injury has resulted where it 

 has been carefully applied. It contains more heavy oils and con- 

 sequently does not penetrate the bark so readily, and the light oils 

 evaporating leave the heavy oils on the bark for some months, 

 which aids in preventing young scales from getting a foothold. 

 Crude oil for use as an insecticide should have a specific gravity of 

 from 43 to 45 Beaume scale, and is sold by certain Eastern com- 

 panies as " insecticide oil." 



