10. Lime. Of no avail whatever.
11. Lye. Concentrated lye is very frequently recommended. In the New Zealand Parliamentary Papers (Codlin Moth Committee Report, 1885, page 7) several statements will be found apparently most favourable to it; yet in places we find admissions that "it cannot reach all the eggs." In America generally, it has not been found satisfactory: "inferior to kerosene in killing-power, and far more injurious to trees when used in solutions strong enough to be effective as insecticides."
It is quite possible that the action of lye on the fungus accompanying the scale-insects (see Chap. III.) may have led "practical" gardeners to imagine that it cleaned their trees of scale. Comstock says, "I saw most excellent results from the following mixture: 1lb. concentrated lye, one pint gasoline or benzine, half pint oil, five gallons water." Probably the good results here were due, not to the lye, but to the gasoline and oil.
12. Pyrethrum. Useless against Coccids (Comstock).
13. Salt. Useless (Comstock).
14. Soap. Undoubtedly a valuable remedy, and perhaps, in some cases, as efficient as kerosene; but it does not destroy the eggs. A solution of 3/4lb. of soap to a gallon of water, applied hot, was entirely successful in California: three months after its application no living scale-insect could be found (Comstock). The time of the year is not stated. In another case the solution was applied cold: "four days after no living insect could be found;" but, again, the time of the year is not stated, and no mention is made of the eggs. Still, a strong solution of soap may be said to be one of the best remedies against the larvæ and adult insects—proportions from 1/4lb. to 1/3lb. soap to one gallon of water (Comstock; Hubbard; Personal experiment).
15. Soda, caustic. Strongly recommended by many persons. It injures the tree, and does not kill the eggs—two things which are decidedly against its use. Gardeners may have been led to employ it from finding that in some instances it clears away the black fungus-growths (Chap. III.), and imagining this to be a clearance also of the scales.
16. Soda, silicate. Kills some insects, but no eggs, and injures the tree (Hubbard).