3. Ashes. Powdered, or mixed with lime, salt, soot, &c. Of no value whatever (Hubbard; Personal experiment).
4. Carbolic acid. Of no avail, either as spray or brushed on, unless used in such strength as to seriously damage the tree (Hubbard; Riley; Comstock).
5. Castor-oil. Has been found efficacious in cleaning hawthorn-trees at the Agricultural College, Lincoln (T. Kirk). It was mixed with soot for some unexplained reason. The time of the year when it was applied is not stated; but the author's experiments seem to show that castor-oil does not effectually kill the eggs. Still, it is doubtless a valuable remedy if applied repeatedly, so as to kill larvæ and adults, supposing it to be sufficiently cheap.
6. Cole's Insect-exterminator. Apparently a mixture of about 2 parts of "green soap" with 100 parts of strong alcohol. It is "effectual as an insecticide, and harmless to growing plants;" but "the cost is too great, except on a small scale, as in conservatories" (Comstock).
7. Gasoline. Seems to have been used in California on pear-trees: result, doubtful (New Zealand Parliamentary Papers: Codlin Moth Committee Report, 1885, page 8).
8. Gishurst compound. Very favourably spoken of in many quarters. In New South Wales it has been found efficacious on orange-trees against Aspidiotus coccineus (Alderton); in Nelson it is said to be used beneficially against Icerya purchasi. It does not, however, kill the eggs with certainty (Personal experiment). Applied warm, and properly diluted, it may be recommended as a good remedy; but applications of it should be repeated.
9. Kerosene. Seemingly the most valuable of all remedies, when properly applied. "Almost the only substance which will certainly kill the eggs without at the same time destroying the plant" (Hubbard).
But the application of this remedy must be carefully performed. Some trees may endure it without injury, even undiluted or unmixed; but this is scarcely to be expected, and the oil should therefore be applied in some mixed form. Also, it is important to remember that a hot sun increases the injurious effect of kerosene; consequently winter, or cloudy weather, should be chosen for its employment.
(a.) Pure kerosene. As just stated, it is probably not advisable to use this. Still, "a young shoot of orange, not more than fourteen days old, was uninjured by an application of pure kerosene which thoroughly wet every leaf;" (Comstock); and Lecanium hesperidum on ivy, similarly treated, was destroyed, without injury to the plant (ibid.).
(b.) Kerosene and milk. An excellent mixture, if milk can be obtained cheap (Riley; Hubbard; Comstock). It must be applied in the form of an "emulsion," sprayed over the tree or brushed on the bark. Hubbard gives the following directions for use: Heat the milk nearly to boiling-point and mix with double the quantity of kerosene; churn violently from ten minutes to half an hour, according to temperature, until a creamy thick fluid is obtained; dilute this with nine or ten times the quantity of water. The mixture is of course purely a mechanical one, as far at least as the water is concerned, and it must be kept constantly stirred, to prevent the substances from separating from the water. For evergreen trees impel the mixture on leaves and branches in the finest possible spray. Sour milk is as useful as fresh.
The object of the milk is not only to lessen the injurious qualities of the kerosene, but also to induce it to mix more freely with the water; but it is the oil alone which destroys the insects and their eggs.
(c.) Kerosene and soap. When milk is not obtainable, or too dear, nothing is so excellent as this mixture. Soap itself (see below) is a useful insecticide, and in combination with kerosene includes the good qualities of both substances. The cheapest possible qualities of soap will do. The mixture, which is, even more than the last, purely mechanical, must be made first of all an "emulsion." The American experiments result in the following recipe and method of using:—
| Formula: | |
| Common soap | ½lb. |
| Kerosene | 2 galls. |
| Soft water | 1 gall. |
Dissolve the soap in the water heated to boiling, then add the kerosene, and churn the mixture until a creamy fluid results which thickens on cooling. Dilute with nine or ten times the quantity of water: the quantities given above will make about thirty gallons of liquid. Whale-oil soap, soft-soap, or any other kind will do. As with the milk emulsion, apply in the form of the finest spray for evergreens (Riley; Hubbard; Personal experiment).
(d.) Kerosene and oil. Castor-oil, linseed-oil, whale-oil, may be used. A mixture of this kind, in the proportion of 1 part kerosene to 3 or 4 of oil, has been found very efficacious for apple- and other fruit-trees attacked by the common apple-scale (Myt. pomorum). But, as observed above, the mixture must not be laid on too thick. Thinly brushed all over trunk and branches, at dead of winter, it has been found quite successful in destroying both insects and eggs, without injury to the trees (Personal experiment). It would probably not answer for evergreens, on account of expense.
On the whole, it may be said that, as far as certainty can be attained in the matter, there is no substance better for destroying Coccids and their eggs than kerosene in the form of milk or soap emulsion, diluted with water for evergreens or for trees with insects on the leaves as well as on the bark. Probably, for deciduous fruit-trees the kerosene-and-oil mixture is the best.
The great point in favour of this substance is that it destroys the eggs; this, few if any of the others will accomplish.