Dec. 1, 1899,] THE TROPICAL AGRICULTURIST, 
375 
REMEDIAL MEASURES AND 
INSECTICIDES. 
• By E. E. Green, Government Entomologist. 
{Coi eluded from page 800.) 
Kerosene Emulsion. — Soap is often combined with 
other ingredients. Of these kerosene emulsion is the 
best known and most widely used. As its efficicy 
and its effect upon plant life very greatly depend 
upon the preparation of the mixture, great care 
should be taken to accurately follow the directions. 
The formula in general use is :— 
Soap I lb. 
Kerosene 2 gals. 
Soft water.. .. .. .. 1 gal. 
' Dissolve the soap in the water heated to boiling, 
then add the kerosene (to the hot mixture), and 
churn it until a creamy fluid results, which thickens 
on cooling, and adheres to glass «ithout separating 
into oily particles.' 
Whale-oil soaps are preferable, but any kind may 
be used. I have personally made a very successful 
emulsion, employing the common country soap, which 
seems to be particularly well adapted to retaining 
the oil in an intimate mixture, and which, in this 
combination, loses its own objectionable properties- 
The most important part of the process is the 
churning. This must be most thoroug;hly carried 
out. It can be satisfactorily managed by repeatedly 
drawing up and expelling the mixture through an 
ordinary garden syringe or a force-pump. A more 
lengthy method is to stir the mixture vigorously 
•with a whisk of twigs. The liquid should be boiling 
hot during emulsification, and then, if kept in a cool 
place, it is said to last for a year or more without 
separating. If insufficiently churned, the mixture 
will afterwards become separated, and tlie oil collect 
at the top. A properly compounded emulsion will 
mix with water in any proportions. 
For use against scale insects a strength of one 
part emulsion to ten of water is found to be effective. 
As in all preparations of which petroleum is an 
ingredient, it can be more safely used on cloudy 
days. When used in hot sunshine, it is liable to 
burn the foliage and injure the tender shoots of the 
plant, but the danger of injuring is much less with 
a properly prepared emulsion than with mechanical 
mixtures of kerosene and water. Mr. Marlatt, in 
some 'Notes on lusectides,'* gives the following 
particulars of experiments which show that kerosene 
emulsion can be used of considerable strength 
without causing appreciable injury to the plants. 
But it cannot be recommended for general use at a 
greater strength than mentioned above. Mr. 
Marlatt writes: 'About the 1st i^ay, when the 
foliage was in the vigour of its early growth, a 
number of plants — peach, Japan quince, elm, pine, 
and strawberry — were treated with the following 
strengths of kerosene and whale-oil soap emulsions, 
made after the standard formula: Diluted (1) with 
2 parts of water, (2) 4 parts of water, (3) 9 parts of 
water, and (4) 14 parts of water, or the emulsion 
at J, 1-5, 1-10, and 1-15 strength. The application 
was very thorough, and the limbs and twigs were 
thoroughly wetted by immersion in the insecticide. 
The treatment was made on a very bright, warm 
day, in the early afternoon. No rain occurred for 
four days, after which there were heavy rains. No 
injury whatever developed in the case of the pine, 
strawberry, and elm with any of the strengths used. 
With peach the injury was trifling, a very small 
percentage, perhaps one or two per cent, of the 
leaves turned yellow and fell to the ground, but I 
am inclined to believe that this was merely the 
jiormal 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 apear on the leaves, and later, 
^. .* Insect Life, vol. vii. p. 116. 
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 healthy and green, had evidently been 
injured more than their surface appearance indicated. 
With No. 2 this peculiarity was almost uunoticeable, 
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 
plans 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. Oare 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 emnlsion a very 
valuable remedy against scale and other insect pests. 
Milk may be substituted for the soap in the manu- 
facture of kerosene 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 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 statements as to the comparative effect- 
iveness of the milk and soap emulsions. 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 aa 
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 undoubtedly effective aa 
an insecticide. 
But in to many cases it is equally fatal to plant 
life. Reports are very 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 of oil at the 
base of the tree, the roots being apparently much 
more sensitive to injury than the exposed parts. As 
a precaution, earth should be banked up round the 
base of the tree, and only sufficient oil should be 
used to moisten the surface of the foliage and 
bark without any surplus to run down the stem. 
Mixtures of kerosene and water have been largely 
mployed in America, and elaborate machines devised 
for ensuring the proper mixture of the two ingred- 
ients. But under any circumstances theireffectivenesa 
does not compare favourably with a properly com- 
pounded emulsion. 
Referring again to one of Mr. Marlatt's reports,* 
I find it stated that 'kerosene mixed with waicr is 
not nearly so powerful an insecticide as the keiostue 
soap emnlsion. It does not remain nearly so long 
on the plant, and is not nearly so effective an 
insecticide at the same strength of oil. The heavier 
soap or milk emulsions kill more effectively, which 
is, perhaps, explained by the heavier liquid actually 
* Bulletin, No. 9 (New Series), U.S. Department 
of Agriculture (Division o£ EntomQlogy). 
