137 



normal spring shedding of the leaves, which is seen in nearly all plants. 

 In the case of the Japan quince, however, with the two stronger mixtures, 

 namely, those with one-third and one-fifth kerosene emulsion, a few 

 yellow spots appeared on the leaves, and later, upon handling the limbs 

 treated with the strongest mixture, about one-fourth of the leaves were 

 found to fall off readily. These leaves, while looking comparatively 

 healthly and green, had evidently been injured more than their surface 

 appearance indicated. With No. 2 this peculiarity was almost unno- 

 ticeable, and with Nos. 3 and 4 no injury whatever was shown, nor did 

 any further injury manifest itself throughout the season in the case of 

 any of the plants treated. These experiments would indicate that the 

 kerosene emulsion can be applied in much stronger dilution to tender 

 foliage of growing plants than has hitherto been supposed.' 



On the other hand, there are well-authenticated reports of plants 

 seriously injured, or even killed, by the use of too strong a mixture, 

 and the application during sunny weather is attended with danger. In 

 my own experience I have found the tender shoots on a recently pruned 

 tea bush to be completely killed back by a comparatively weak mixture 

 applied during sunny weather. 



When the foliage of a plant is attacked, the applications should be 

 made by means of a spraying machine. In the case of pruned trees, 

 when the pest affects the bark only, the liquid can be applied with a 

 brush or a piece of rag to the stems and branches. Care must be taken 

 that the liquid is not used in sufficient quantities to run down and 

 saturate the roots of the plant, or grave injury may result. When 

 employed with proper precautions, there is no doubt that we have in 

 kerosene emulsion a very valuable remedy against scale and other insect, 

 pests. 



Milk may be substituted for the soap in the manufacture of kero- 

 sene emulsion. The formula given by Hubbard is : — ' One part milk 

 (sour milk is said to be as suitable as fresh for the purpose), to two 

 parts kerosene. Heat the milk nearly to boiling point and mix with 

 the kerosene. Churn the mixture violently until a thick creamy fluid 

 is obtained. For use against scale insects dilute with nine or ten times 

 the quantity of water.' I have been unable to find any definite state- 

 ments as to the comparative effectiveness of the milk and soap emul- 

 sions. It is possibly a question of cost. In some countries a gallon of 

 milk may be cheaper than half a pound of soap ; but in most places it is 

 probable that the balance of advantage will be on the other side. The 

 active insecticidal properties of soap itself must surely be an additional 

 advantage. 



Kerosene. — Much diversity of opinion exists as to the use of pure 

 kerosene or a mechanical mixture of kerosene and water. It is un- 

 doubtedly effective as an insecticide. 



But in too many cases it is equally fatal to plant life. Reports are 

 yery conflicting. In some cases spraying with the undiluted oil has 

 been unattended by any injury to the tree, while particularly successful 

 in killing the scale. In other cases even large trees have succumbed 

 under the treatment. One cause of injury is said to be the collection 

 offoil at the base of the tree, the roots being apparently much more 



