This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
Prof. W. Saunders, of the Province of Ontario, followed Mr. Zimmerman with a paper on other departments of the same general subject, which contained much information and many suggestions of great value to cultivators. He had found Paris green an efficient remedy for the bud-moth on pear and other trees. He also recommends Paris green for the grapevine flea beetle. Hellebore is much better for the pear slug than dusting with sand, as these slugs, as soon as their skin is spoiled by being sanded, cast it off and go on with their work of destruction as freely as ever, and this they repeat. He remarked that it is a common error that all insects are pests to the cultivator. There are many parasites, or useful ones, which prey on our insect enemies. Out of 7,000 described insects in this country, only about 50 have proved destructive to our crops. Parasites are much more numerous. Among lepidopterous insects (butterflies, etc.), there are very few noxious species; many active friends are found among the Hymenoptera (wasps, etc.), the ichneumon flies pre-eminently so; and in the order Hemiptera (bugs proper) are several that destroy our enemies. Hence the very common error that birds which destroy insects are beneficial to us, as they are more likely to destroy our insect friends than the fewer enemies. Those known as flycatchers may do neither harm nor good; so far as they eat the wheat-midge and Hessian fly they confer a positive benefit; in other instances they destroy both friends and enemies. Birds that are only partly insectivorous, and which eat grain and fruit, may need further inquiry. Prof. S. had examined the stomachs of many such birds, and particularly of the American robin, and the only curculio he ever found in any of these was a single one in a whole cherry which the bird had bolted entire. Robins had proved very destructive to his grapes, but had not assisted at all in protecting his cabbages growing alongside his fruit garden. These vegetables were nearly destroyed by the larvae of the cabbage fly, which would have afforded the birds many fine, rich meals. This comparatively feeble insect has been allowed by the throngs of birds to spread over the whole continent. A naturalist in one of the Western States had examined several species of the thrush, and found they had eaten mostly that class of insects known as our friends.
Prof. S. spoke of the remedies for root lice, among which were hot water and bisulphide of carbon. Hot water will get cold before it can reach the smaller roots, however efficient it may be showered on leaves. Bisulphide of carbon is very volatile, inflammable, and sometimes explosive, and must be handled with great care. It permeates the soil, and if in sufficient quantity may be effective in destroying the phylloxera; but its cost and dangerous character prevent it from being generally recommended.
Paris green is most generally useful for destroying insects. As sold to purchasers, it is of various grades of purity. The highest in price is commonly the purest, and really the cheapest. A difficulty with this variable quality is that it cannot be properly diluted with water, and those who buy and use a poor article and try its efficacy, will burn or kill their plants when they happen to use a stronger, purer, and more efficient one. Or, if the reverse is done, they may pronounce it a humbug from the resulting failure. One teaspoonful, if pure, is enough for a large pail of water; or if mixed with flour, there should be forty or fifty times as much. Water is best, as the operator will not inhale the dust. London purple is another form of the arsenic, and has very variable qualities of the poison, being merely refuse matter from manufactories. It is more soluble than Paris green, and hence more likely to scorch plants. On the whole, Paris green is much the best and most reliable for common use.
At the close of Prof. Saunders' remarks some objections were made by members present to the use of Paris green on fruit soon after blossoming, and Prof. S. sustained the objection, in that the knowledge that the fruit had been showered with it would deter purchasers from receiving it, even if no poison could remain on it from spring to autumn. A man had brought to him potatoes to analyze for arsenic, on which Paris green had been used, and although it was shown to him that the poison did not reach the roots beneath the soil, and if it did it was insoluble and could not enter them, he was not satisfied until a careful analysis was made and no arsenic at all found in them. A member said that in mixing with plaster there should be 100 or 150 pounds of plaster to one of the Paris green, and that a smaller quantity, by weight, of flour would answer, as that is a more bulky article for the same weight.