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.
The subject of Mildew, proposed by Mr. Graasie, V. P., was then taken up, by the reading of the following Essay:
Mildew, whether on the Tine, the stems of wheat, the leaves of the chrysanthemum, gooseberry, pea, rose, or peach, is the result of parasitic fungi, the roots of which penetrate the epidermis, rob the plant of its juices, and interrupt its respiration. It is generally admitted that every species of plant has its own peculiar forms of vegetation and animal parasites. Although the same species may not unfrequently be found on different plants, in general they are found in greater abundance on the plants to which they appear to have some affinity. Thus we have the mildew on the peach, the Tine, pea, berberry, Ac.; named and known as such. This much is Admitted, but what we want to ascertain is the cause of its origin. Here we find a diversity of opinion, and, I may add, will likely continue to do so, as on all such subjects.
There are three or four opinions more prominent than the rest, and worthy of our practical investigation; it shall therefore be my object to present those news (as understood by me) to the members, and learn their experience with regard to them.
First, we may take the President's theory of it, in which some of the most practically ob-serring men in this country and Europe coincide. At a former meeting he gave us the result of his practical observation, that plants by nature or habit, natives of a moist climate, introduced into a dryer atmosphere, are victims to mildew; that dry air, as stated in the Theory of Horticulture, acting on the surface of tender vegetable tissue, was favorable to its development, mentioning the lilac and hawthorn as examples. It is a well-known fact, that in dry seasons we hare more mildew than in moist; and I have no doubt all of you who have bad experience with the peach-tree on walls, in Europe, have observed that those trees that got copious syringings were not troubled with mildew, in comparison with those that were left to themselves. We had two or three dry, warm daya this season, in April; with me, English gooseberries, where most exposed, were all mildewed; those in a more moist and shaded position partially escaping.
Again, in sowing peas for fall use, if they get good, copious waterings, they are never much affected with mildew, and all know that in a dry fall turnips are apt to mildew.
The Second Theory is quite the opposite of the first. It supposes mildew to be produced by too much moisture; that is, the leaves absorb an excess of moisture from the atmosphere; the soil is too dry for a comparison with the air; that if damp and cold weather succeed that which has been warm and bright, without a good fall of rain, we are sure to have mildew ; an injurious absorption of moisture by the leaves and stems of the plants takes place, the ascent of the true sap is retarded, a retrograde motion of the fluids is produced, and the plant becomes the food of fungi. I may add that this theory has been very generally accepted as the true one.
The Third Theory is, that fungi are communicated to the plants from the soil, and developed within the tissue, and that they afterwards make their way through the stomata; that every specimen emits annually myriads of minute seeds, (sporules,) and these are waited through the air. They may remain dormant until a convenient season, then vegetate and reproduce sporules; that they have likewise the power of spreading by throwing out offsets-from the roots, so that they are never absent from the soil, but at one period or other are to be found on the plants subject to their attacks.
The Fourth Theory is, that mildew is caused by the distempered juices of plants, and no one ever saw mildew upon the leaves of a healthy, vigorous plant; in short, is not so much in the atmosphere, either wet or dry, although it originates on the surface of plants, but that the tissue of the subject has always been, previous to being attacked, in a diseased state. I have never found mildew attack any grape-vines under my charge but once, some three years ago, and then slightly; it was on the variety called White Nice; the previous fall the wood had not been well ripened; the next spring it bled considerably; the wood produced was unhealthy, watery, and spongy, hence a fit subject for mildew. We have several cures, in the way of sulphur, nitre, common salt, the fumes of black sulphur, hydro-sulphate of lime, etc. But prevention is always preferable to curative operations, and I have no doubt that if vines are kept in due vigor, well drained, the border protected against excesses of either moisture or dryness, and the leaves protected from sudden atmospheric changes, they will never be visited by mildew.
For those who may require a cure, I may mention that I have never found it necessary to cover the bunch and leaves of the grape with sulphur; only simply spreading it about is generally effective. Hydro-sulphate of lime is made of equal parts of quick-lime and sulphur, one pound of each to five pints of water, boiled for ten minutes; to this add one hundred parts more water; let it clear, and syringe with it. Common salt for roses, peas, and similar out-door crops, two ounces to the gallon of water; of nitre, one ounce to the gallon; with this syringe the plants.
After the Essay had been read, quite a discursive debate took place, which we shall not attempt to give in detail. From the points elicited, it may be deduced, that quite a difference of opinion was maintained among the members present. Of the four theories set forth in the essay, it appears two only were held by the speakers. The essayist, while he did not adopt either of them, still appeared to agree with that which attributes mildew to a dry atmosphere.
William Saunders thought the principal object with us should be, not so much to discover the cause of the disease, as to point out a remedy by which its evils might be avoided. We have little to do with the scientific questions involved; our object should be to secure our crop of fruit What is it to us whether mildew does or does not exist in the leaf in an undeveloped state, if we save the crop 7 and this, I hold, can be done by care, and attention to ventilation, etc. It is also my opinion that mildew can not attack a leaf or plant till decomposition is first going on in the tissues of the plant. Much might be said and conjectured as to the causes; what we want is, facts. I place no importance on authorities quoted here.
James Eadie could not admit that mildew only attacked plants already partly decomposed; his observations had led him to different conclusions. He had detected mildew where there was no previous decomposition.