This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
I now send a Peach branch, surrounded by insects that belong to the history of the Peach-tree, as they so largely contribute to that fatal disease, the Yellows; that disease about which so much has been written, and over which so dark a cloud appears to rest, as it has hitherto baffled the skill of the most practical fruit-growers, yielding to no remedy, and in some cases giving the infection to all the trees in the neighborhood.
After years of close attention to the culture of the Peach-tree, I have come to the conclusion, that as soon as the Yellows makes its appearance, the best thing to be done is to cut the tree down and burn it, for all endeavors to restore its health will be lost labor.
I have arrived at this conclusion for the following reasons: The Yellows arises from various causes: first, from soil exhausted of those chemical agents that are necessary for the nourishment of both tree and fruit - agents that have been so abundantly found in the virgin soil of our Middle and Southern States, but which appear to be exhausted by the over-culture of the Peach in the old plantations, but which are as lavishly produced in a new clearing, where Peaches have never been raised: there may be seen Peach-trees, growing in all their pride and glory, and crowned with their rich foliage and most luscious fruit, if they can be protected from late frosts, and their deadly enemies, the insects. A late frost, if severe enough to freeze the sap in the tender and delicate sap-vessels, will be fatal to the tree: though it may linger through the spring and early summer, the effect of impeded circulation will show itself in the exhausting heats of July and August, and the spurious yellow growth will tell the tale that death is inevitable.
The tree had better then be cut down, for it is only a cumberer of the ground.
The next deadly enemy is the well-known peach-borer, the AEgeria exi-tosa of Say. This wasp-like insect may be seen hovering around the roots and lower parts of the trunks of the trees, in the bright noondays of June and July, seeking a tender spot where she may thrust her eggs into the sap-vessels of the inner bark, where the young grubs find their food. If undisturbed by the guardian spirit of the orchard and forest, the woodpecker, or by the pruning-knife of the gardener, the little grub feeds in secret on the vital principle of the tree, gnaws its tortuous path around the trunk, and, as winter approaches, seeks shelter under ground among the roots, feeding on them until the following spring, when it gradually gnaws its way to the lower part of the trunk; it then leaves the tree, and a little beneath the surface of the ground, among the gum and castings that have exuded from the wounded bark, it forms the follicle No. 3 around itself, and, simulating death, awaits its change.
In the early mornings of June the perfect fly may be seen bursting the upper end of the follicle, and gradually emerging from its tomb. At first its delicate wings are wet, and closely rolled about its body. When it has painfully struggled out of the pupa case, No. 4, it clings to the follicle for a few minutes to rest; then it crawls to the trunk of the tree, takes firm hold with its claws of the rough bark, and, with its head upwards, gradually unrolls and expands its wings; the juices from its swollen body rush like rills through the veins of the pendent wings, and in half an hour they will have stretched to their full size and beauty. The upper wings and body of the female, No. 1, are opaque, and of a fine steel blue metallic color, while the under wings are transparent, and glisten with the irised hues of the rainbow; the middle of the body is adorned with an orange-red band, which adds brilliancy to its light and delicate form. The male, No. 2, is smaller than its mate, its body and legs are steel blue, and all four of the wings clear and beautifully iridescent; all the wings are edged with a dark blue fringe, and the upper pair have a dark wedge-shaped band near the outer extremity.
If the grubs are carefully searched for, and taken from the roots in the months of August and September, the trees may be saved; but if they are allowed to feed unmolested, and girdle the trunk and roots, which is their habit, the yellow and exhausted branches tell the tale that death is inevitable; therefore, cut the tree down and burn it, for it cumbereth the ground.
No. 6 is a magnified drawing of No. 5 - the Tomicus liminaris. This minute beetle is believed to be the cause of the infectious Yellows. The Tomicus is strictly a bark-beetle, as both larva and beetle feed on the sap-vessels of the inner bark of the Peach-tree; they may be found in the grub state in the months of July and August, and if numerous will destroy the tree in which they feed, producing an irritation analogus to the itch in the human species. I have seen them in such numbers that one of these minute grubs was found in every pore of the bark, from the top branch to the root; a swelling of the sap-vessels ensued, and spurious yellow shoots were thrown out from every bud; entire exhaustion and death of the tree soon followed; the grubs became pupa, and changed to beetles in the dying tree, and then took wing and made their home in the nearest tree, which they soon killed in like manner. Thus the infection spread from tree to tree, until ten trees were destroyed before the cause of their death was discovered.
In this case it was evident that no care could save the infected trees or protect • the healthy ones, but cutting the sickly trees down and burning them, thus destroying this minute but powerful enemy.
In this sad picture there is one bright gleam, showing the beautiful order of the great Creator, who formed these grubs to restrain the undue growth and increase of the fruit-tree, and now provides a check on them, and sends the Ichneumon, our watchful friend and protector. Ever on the wing, or with a quick, light step and jerking motion, it glances from place to place, inces-r santly tapping the spot on which it alights with its long and delicate feel-Zers, seeking a home for its young, which it finds in the bodies of living grubs and caterpillars. The moment the Ichneumon discovers the spot where a grub is concealed, it pierces the bark with its sword-like ovapositor, and with unerring instinct darts the egg into the fatty part of the grub, which the young Ichneumon feeds on, never approaching the vital parts, as the continued life of the grub is necessary to its own existence; thus they both feed on until the time of change approaches: then the exhausted grub spins a feeble follicle, in which it dies, while the Ichneumon passes through its deathlike sleep in safety, and at the appointed time comes forth a perfect fly, to carry on the work of destruction as its parent had done.
The Peach-trees may be protected from the AEgeria by covering the lower part of the trunk and exposed portions of the root with a plaster of rosin and grease, thick enough to prevent the fly from depositing her eggs in the bark.
Miss Morris has proved, to my satisfaction at least, that the theory of the cause of the yellows, promulgated by her in vol. 4th, p. 502, of your journal, is the correct one. Peach cultivators are under great obligations to her for the careful researches by which she has arrived at her conclusions, and the lucid descriptions by which she makes known their results. Not having the good fortune to inhabit a peach-growing district, my acquaintance with the disease is chiefly theoretical, but I have never seen an explanation of its cause which appeared so conclusively true upon its face, as the one in question. Were cultivators to dig up and burn without remorse all affected trees, I am convinced that the disease would soon be eradicated.