This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
We desire to introduce this subject as surreptitiously as possible. It is one which is supposed to have the same effect upon an editor as a red rag has upon a bull. It is a well known fact that last year the editorial sanctums were infested with the Botrytis infestans in a desperately aggravated form; and we heard of one editor "who was, by his own confession, positively "sick of the disease;" and who resorted to disinfecting measures of the most rigorous description for stamping it out. His plan was by fire. Every missive supposed to contain "spores," either "resting" or "active," was carefully reconnoitred and then transferred to the flame. It is needless to say that the plan was completely effectual.
We have an impression that scientists carry themselves rather loftily in the disease matter. They know what it is, and how it comes; they have traced the destroyer to his very lair, but they have not caught him. "Whenever the disease is worse than usual, the "practicals" are down directly with a host of facts and suggestions, which our philosopher treats in a half patronising, half supercilious manner. These things are not new to him! 0 dear, no! There is no mystery about the potato disease, none whatever. Mr Fungophobia has long ago pointed out the cause, and no measures for its prevention which are not based upon Fungophobia's theory, can possibly be attended with success. They feel it their duty to impress this upon the public, as they have often done before, and they reproduce Fungophobia's statements, and trot out his procession of queer-looking objects, having a strong resemblance to tadpoles, and which the potato-grower is told he must catch, drown, suffocate, or do away with in some way or other, before his emancipation comes; all of which appears to the practical common-sense farmer like a proposal to bottle up the wind, and quite as feasible.
For anything he knows, he may be carrying thousands of "resting spores" among the hairs of his head, and setting a colony sufficient to infest a whole district at liberty every time he takes his hat off in the field, unless disinfecting measures begin upon his own person.
But seriously, is it possible that a disease which affects other plants beside the potato, which is so subtle in its development, and which spreads with a rapidity entirely beyond our comprehension, is likely to be stamped out or even abated by any measures of a merely disinfecting kind, supposing the fungus theory to be correct, which is disputed by not a few thinkers? It is certain that the potato disease was almost unknown before 1845, but the Botrytis infestans was familiar enough to fungologists before that time. What then caused it to attack the potato with such virulence all at once? This has never yet been explained, and the fact has led many to believe that the fungus is but the consequence not the cause of the disease. There is no doubt about the presence of the parasite in every diseased potato, but it is just as likely as not that it came there because the conditions for its development were favourable, in the same way that mildew can be produced upon the Vine by certain treatment, and made to disappear when that treatment is altered.
I confess to having little or no hope that we shall ever be able to eradicate the disease altogether, though we may check it; but who can say that such a mysterious disease may not disappear eventually in the same mysterious manner that it came.
It is certainly not a little humbling to think that the painstaking investigations and discoveries which have been made on the subject should have led as yet to no practical results.
The disease was at first attributed to the cold and wet by every cultivator of the potato; and although that may be only the indirect cause, it has always appeared to practical minds as the evil against which all preventive measures must be directed; and no discoveries which have been made, though they have made us more familiar with the characteristics of the disease, have altered this view of the case. If the rainfall is above the average at a certain time of the year, the farmer knows by sad experience that all hopes of a sound crop are at an end, and vice versa, if the summer is warm and dry. We never knew of an instance in which protection from the wet was afforded, either accidentally or otherwise, but the crop was good. The first instance of this kind which came under our notice was remarkable, as showing that dryness of the soil, whether that is secured by drainage or otherwise, is a preventive. In a quarter of potatoes which I had to do with, there grew a tree - an ash, if I recollect aright. It was a round headed tree, with a stem about 8 or 9 feet high, so that the ground could be cropped very nearly up to the stem. "When the potatoes were taken up, they were very badly diseased, except those under the tree; and they, though smaller, were nearly every one sound.
What with the shelter afforded by the branches, and the absorption of the moisture from the ground by the tree-roots, which were massed near the surface so thickly that a fork could scarcely be used, the soil was as dry and mealy as possible. Now there was no shelter here to speak of from anything but the wet, for owing to the height of the stem, the potatoes under the tree were exposed fully to the blast from the south, east, and west. I attributed the dryness of the soil chiefly to the roots of the tree. It is well known how surface-rooting trees rob the soil of its moisture. Since then, many instances of the same kind have come under our observation, as they must that of others. Last year, a farmer in this neighbourhood planted a quantity of Irish Rocks in a field where the soil was thin and dry. In October they turned out a sound and excellent crop. Part of the same lot was planted on the same formation, but in the hollow, where the soil was deeper and wetter, and they turned out an utter failure. We went over a rather badly diseased field of potatoes last autumn, poking out the tubers we could see protruding above the surface of the soil; only one of these we found diseased, and not badly.
Were it needful we could give many more instances, and also experiments, all proving that the wet is the enemy we have to contend against, and nothing else. Farmers and gardeners must of course crop the land they hold, but they should select the driest, and plant shallow. Would it not be worth while also, for farmers in those districts where the soil is poor and thin, to plant potatoes more extensively - turn potato-farmers, in fact ? In such districts thicker planting could be practised to make up for shorter but sounder crops. We have seen a poor gravelly brae turn out a comparatively sound crop many a time when the rich meadow was a complete failure.
A good deal has been said at different times about the advantages of a change of ground. A gardener would not think of cropping the same quarter with potatoes two years in succession if he could help it; but how do the cottagers get on 1 I know many plots and allotments that have been cropped with potatoes year after year for more than ten years, and yet the crops, to my knowledge, are always first-rate, to say the least of them, where the ground has got an occasional liming and a moderate dressing of manure annually. As fine a patch of " Sutton's Flour Ball" as I have seen anywhere this season is in a garden which has been cropped with potatoes for nearly fourteen years. The soil is not a good spade deep, for it never was trenched.