This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Winter Moth (Cheimatobia brumata), Mottled Umber Moth (Hybernia defoliaria), Early Moth (H. rupicapraria), March Moth (Anisopteryx wscularia), Figure-of-8 Moth (Diloba cairuleocephala), Goat Moth (Cossus ligniperda), Wood Leopard (Zeuzera pyrina), Vapourer Moth (Orgyia antiqua), Plum Tortrix (Penthina pruniana), Allied Bud Moth (P. variegana), Codlin Moth (Garpocapsa pomonella), Red - legged and Clay-coloured Weevils (Otiorhynchus tencbricosus and 0. picipes), Leaf Weevils (Phyllobius sp.), Plum-leaf Sawfly (Cladius padi), Slug-worm (Eriocampa limacina), Social Pear Sawfly (Pamphilus fiaviventris), Hop Damson Aphis (Phorodon humuli, var. malaheb), Oyster-shell Bark Louse (Aspidiotus ostrewformis), Mussel Scale (Lepidosapthaes ulmi), Brown Scale (Lecanium caprew), Leaf Hoppers (Typhlocybidce), Plum-leaf Gall Mites (Eriophyes padi, &c), Red Spider (Tetranychius telarius).
[f. v. t.]
Silver Leaf, - The Plum has diseases peculiar to itself, as well as sharing in others common to the Apple and the Pear. The worst of all is what is called " Silver Leaf", from the peculiar sheen on the foliage which is the first evidence to the eye that the tree is smitten. The disease, which seems to have been first mentioned in Mr. J. Weathers' Practical Guide to Garden Plants, published in 1901, attacks Apples sometimes, but not Pears; in Plums it has become so serious as to threaten with extinction the cultivation of the " Victoria" in some parts. So far, no authoritative statement has been made as to what is a remedy for it, although it has been proved to be due to a fungus called Stereum purpureum.
In The Fruit Garden the disease is not even mentioned, and yet it is responsible for the death of thousands of Plum trees every year. In one mixed plantation in Middlesex, out of a quarter containing 8 ac. of Victoria Plums and Apples, over 300 trees were thrown up in the winter of 1909-10. These trees were fifteen years old, and therefore just in their prime. The disease is not confined to any one part of the country, and a drive in any district where Plums are cultivated will show the patches of silvered foliage which tell that the tree is doomed, and each year it extends its ravages. Some varieties of Plums seem more susceptible than others; the "Victoria" and "Prince of Wales" appear to be the worst, but none are immune.
Cultivation seems to make little difference; it can be seen where the work is done properly, the trees watched and attended to, and the land kept clean, as well as where nothing is done to the trees, and the weeds are allowed to cheat the labourer of his hire. In fruit gardens and grass orchards it is all the same. Rumours are sometimes current that someone has found a remedy, but up to now it has failed to crystallize. Once it was the insertion of sulphate of iron to the trunk and branches of the tree by boring holes 1 1/4 in. diameter and plugging them with Portland cement, which had cured all the diseased trees on one plantation; next, it was the application of 3 lb. sulphate of iron to the roots by forking it in, repeated each winter for three years, that had worked the cure. Probably we shall hear more of the effect of the above and other methods of treatment, for many are trying them. It seems to be generally agreed that the application of lime and sulphate of iron is in the track of a remedy. But how much of each, and how to apply them? Does the composition of the soil make any difference to the amount or proportion of each required, and are other ingredients likely to be needed in some soils? All these and many other questions can only be answered by careful and exhaustive experiments, scientifically arranged and managed and carried over a series of years. Who is to do it? Where is the Government experimental farm, or, better still, where is the agriculturists' joint experimental farm? The market grower, whatever scientific training he may have, however much he may desire to obtain accurate data, is ill qualified to carry out such experiments. His business is to obtain by the cultivation of the soil a profit upon his outlay and an earning for his labour of brain and muscle which shall afford him the means of a livelihood. In this pursuit there come things that must be done at a certain time, and at the same time some investigation in connection with the experiment must be made or some data noted, and it is the latter that has to go, so the detachment and continual attention necessary to obtain reliable data from the experiment cannot be given.
If the Board of Agriculture ever were desirous of doing something in this line, a plan more effective and immensely less expensive than the establishment of one experimental farm might be adopted. That is, stations for experiment might be established on farms in different counties by arrangement with the cultivators, who would do the work, as directed, for agreed payment, and the data noted by scientists who would pay regular visits for that purpose. The advantages gained would be that the experiments, being spread over several counties instead of being confined to one spot (the experience gained at which could never be held to apply to the whole kingdom), would be brought under the eyes of growers, who would take more interest in them and learn more from them than they would from what is done at an experimental farm which many of them would never be able to visit, and the literature of which they might never read; finally, the saving of expense.
As things are, the grower must make what experiments he can. He will find, as has been said, the use of lime, sulphate of-iron, and also sulphate of potash useful. The disease is said to be highly contagious, able to transfer itself from tree to tree by means of spores carried on the wind when liberated from the decaying wood it has killed. To make sure, all wood cut from affected trees should be quickly burned, and the saw or knife, after cutting on an affected tree, should be dipped in some antiseptic fluid before being used on another tree. When a tree is badly diseased the only thing known at present to do is to root it up. Before planting another, the hole should be broken up deeply and 3 lb. of sulphate of iron sown over it, and a day or so after 15 lb. freshly slaked lime. [w. g. l.]
This disease, Silver Leaf, is much in evidence at the present day, both at home and in countries as far distant as New Zealand. The symptoms are a change from the normal green colour of the leaves to a dull lead or silvery tint. During the first season of attack usually only a few branches here and there show the disease; the second year, as a rule, all the leaves on the tree are attacked, and very frequently during the third year the tree dies outright. It is believed by some that this disease is caused by a fungus called Stereum purpureum, and the evidence in support of this belief appears to be so convincing that it has to be admitted that the fungus can cause Silver Leaf. On the other hand, it is more than doubtful as to whether the enormous increase of the disease during recent years in many parts of the world is all due to Stereum purpureum, a very common fungus in this country. Why has this fungus only recently attacked Plum trees?
Apart from this question, however, it is important to remember that when a tree is once attacked, as a rule it does not recover, and should be replaced at once by another tree, which does not become diseased through occupying the place of the diseased tree. Not more than a dozen cases are on record where a diseased tree has recovered out of the thousands that have been attacked.
No cure is known. As a preventive measure all Stereum purpureum, a fungus forming purplish or lilac crusts on dead branches, should be removed and burned. When old, the fungus becomes bleached and almost white.
Gumming", See p. 52. [g. m.]