CHAPTER IV
STOCKS AND RESISTANT VINES
Phylloxera, a tiny root-louse, made its appearance in France in 1861 and began multiplying with a fury unparalleled in the insect world. By 1874, the pest had become so widespread in Europe that it threatened the very existence of the great vineyard industry of that continent. All attempts to bring the pest under control failed, although the French government offered a reward of 300,000 francs for a satisfactory remedy. Numerous methods of treating the soil to check the ravages of the insect were tried, also, but none was efficacious. Finally, it dawned on European vineyardists that phylloxera is not a scourge in America, its habitat, and that European vineyards might be saved by grafting Vinifera vines on the roots of immune American grapes. At once the reconstruction of vineyards in Europe was begun by grafting the grapes on phylloxera-resistant roots. Meanwhile, consternation spread to California when it was discovered that phylloxera was running riot in some of the vineyards of the Pacific slope; however, with the knowledge derived from viticulturists in Europe, they too began reconstructing vineyards on immune roots, without the same success as the Europeans, it is true, but with such measure of success that it soon became the approved method of growing grapes in this great region.
Through the use of resistant stocks, phylloxera is now defied in Vinifera regions. Millions of American stocks are annually struck at home, in Europe and wherever Vinifera grapes are grown, to be top-worked with varieties susceptible to phylloxera. Seldom has mastery over a pest been so complete; but, to triumph over the tiny insect, the industry has had to be revolutionized. Resistant stocks, in their turn, brought innumerable new problems, many of which are still unsolved. Investigations and experiences in rehabilitating vineyards have been carried on for forty years, the results set forth in books and bulletins and yet there are many problems to be solved. The grape-grower in regions infested with phylloxera is always under the necessity of taking advantage of the latest demonstration of practices in the use of resistant stocks. These practices are best studied in the experiments of state experiment stations and the United States Department of Agriculture, and in the vineyards of leading grape-growers, since even those most needing elucidation can be but briefly discussed in the following paragraphs.
The wild vines of a species are always seedlings and are hence exceedingly variable. The first vineyards of resistant stocks were vines grafted on stocks of wild vines, and the results were very unsatisfactory; for, naturally, there was divergence in many characters and especially in the vigor of the vines. Also, there was difficulty in grafting, since some wild vines are stout and others slender; some bear grafts well, while others do not. It soon became apparent that to succeed, varieties must be selected from the different species for vineyard work. The great task of the experimenter and grape-grower, therefore, has been to select varieties of the several species sufficiently resistant, vigorous and otherwise possessed of characters fitting them to become good stocks. Out of vast numbers tested, a few are now generally recognized as best for the several groups of Vinifera grapes and the several distinct regions in which these grapes are grown.
Resistant species and varieties.
The reconstruction of phylloxera-ridden vineyards by the use of resistant stocks is possible only because some species and varieties are, as has been said, more resistant to the root-louse than others. All degrees of resistance exist, as would be suspected, from immunity to great susceptibility. It is obvious that the foundation of the art of growing resistant vineyards is exact knowledge of the immunities and susceptibilities of the many varieties and species of grapes. From the first use of resistant vines, experimenters everywhere have set themselves at work to determine not only what the most resistant vines are, but what the causes and conditions of immunity. In spite of a wealth of empirical discoveries as to what grapes can best resist the root-louse, causes and most of the conditions of immunity are still little understood. Definite, useful knowledge, so far, goes little further than the establishment of lists of species and varieties, the latter subject to change, that are most useful in setting resistant vineyards.
Phylloxera does little damage to species of Vitis native to the same general region in which the pest has its habitat, but nevertheless there are some differences in resistance in American grapes. Munson, one of the best American authorities on the resistance of species to phylloxera, says:[7] "Rotundifolia is entirely immune, then Rupestris, Vulpina, Cinerea, Berlandieri, Champini, Candicans, Doaniana, Æstivalis and Lincecumii are so high in resistance as to be practically uninjured, though they may be attacked, while Labrusca is low in resistance and is much weakened in clay soils, if infested, and Vinifera is entirely non-resistant." Some of these species are hard to propagate and difficult to suit in soil and climate so that but two of them are much used for resistant stocks. The two most used are Rupestris and Vulpina (Riparia), of both of which there are varieties which give satisfaction. Bioletti, a leading authority on resistant stocks in California, says:[8]
"Varieties of resistant stocks which will in all probability be used in California are Rupestris St. George (du Lot), Riparia × Rupestris 3306, Riparia × Rupestris 3309, Riparia Solonis 1616, Mourvèdre × Rupestris 1202, Aramon × Rupestris 2, Riparia gloire, and Riparia grande glabre. These are all varieties which have given excellent varieties for years in Europe, and have all been tested successfully in California. Among them are varieties suitable for nearly all the vineyard soils of California, with perhaps the exception of some of the heavier clays.
"The only one of these varieties which has been planted extensively in California is the Rupestris St. George. There can be little doubt, however, that it will fail to give satisfaction in many soils, and though we may not find something better for all our soils it is probable that we will repeat the experience of Southern France and find that in most soils there is some other variety that gives better results. Without attempting to describe these varieties, but to give some idea of their merits and defects and of the soils most suited to each, the following indications are given, based principally on the opinions of L. Ravaz and Prosper Gervais, and on a still limited experience in California:
"The Rupestris St. George is remarkably vigorous and grows very large, supporting the graft well even without stakes. It roots easily and makes excellent unions with most vinifera varieties. It is well suited to deep soils where its roots can penetrate. Its defects are that it is very subject to root-rot, especially in moist soils; it suckers badly and it suffers from drought in shallow soils. Its great vigor produces coulure with some varieties and often necessitates long pruning.
"In moist or wet soils 1616 or 3306 had given better results in France and gives indications of doing equally well here. In drier soils 3309 will probably be found preferable.
"Aramon Rupestris No. 2 is suited to the same soils as Rupestris St. George, and does particularly well in extremely gravelly soils. It has some of the defects of the St. George and is moreover more difficult to graft, and its only advantage in California is that it is rather less susceptible to root-rot.
"There are no better resistant stocks than Riparia gloire and Riparia grande glabre, wherever they are put in soils that suit them. They do well, however, only in deep, rich, alluvial soils which are neither too wet nor too dry. Their grafts are the most productive of all, and ripen their grapes from one to two weeks earlier than the grafts on St. George. Their principal defect is that they are very particular as to the soil, and they never grow quite as large as the cion. The gloire is the most vigorous, and the difference of diameter is less with this variety than with any other Riparia.
"The Mourvèdre × Rupestris 1202 is extremely vigorous, roots and grafts easily, and is well adapted to rich, sandy and moist soils. In drier and poorer soils its resistance is perhaps not sufficient.
"The most promising varieties for general use at present seem to be the two hybrids of Riparia and Rupestris, 3306 and 3309. They have great resistance to the phylloxera, root and graft almost as easily as St. George, and are quite sufficiently vigorous to support any variety of vinifera. The former is more suited to the moister soils and wherever there is danger of root-rot, and the latter to the drier soils. In general, they are suited to a larger variety of soils and condition than perhaps any other varieties.
"Riparia gloire should be planted only on rich, deep alluvial soil containing an abundance of plant food and humus, what would be called good garden land, such as river bank soil not liable to overflow.
"In most other soils Riparia × Rupestris 3306 is to be recommended, except those that are rather dry, where 3309 is to be preferred, or those which are very wet, where Solonis × Riparia 1616 is surer to give good results."
The value of a species or variety for a resistant stock may be judged somewhat by the visible effect of the phylloxera on the roots of the vines. On susceptible species, the punctures of the insects rapidly produce swellings which vary in size and number in accordance with resistance of the species. Technically, the first swelling on the young tender rootlets of the vine is called a nodosity. The presence of a few nodosities on the root system does not indicate that a vine is not a valuable resistant stock. When the nodosity begins to decay and becomes of a cancerous nature, it is called a tuberosity. These tuberosities decay more or less rapidly and deeply, and when they rot deeply cause enfeeblement or death to the vine. Thus, on Vinifera varieties the tuberosities are several times larger and decay sets in much more quickly than on American species which show these tuberosities. Ratings as to resistance of species are usually made from the size and number of the tuberosities, though when these are found producing a scab-like wound which scales off, there may be high resisting power.
In order to convey with some degree of definiteness the power of resistance to phylloxera, an arbitrary scale has been agreed on by viticulturists. In this scale, maximum resistance is indicated by 20 and minimum by 0. Thus, the resisting power of a good Vulpina is put as 19.5 and that of a poor Vinifera variety as 0.
Adaptations of Resistant Stocks to Soils and Climates
Resistance, of course, counts for naught in a stock which comes from a species unsuited to the soil and climate or other circumstances of the locality in which the vineyard is to be planted. The several species used for stocks differ widely in the requirements affecting growth so that the grower must make certain that the resistant stock he selects will find congenial surroundings. Stocks in congenial circumstances are frequently more resistant than others inherently more resistant, but which are not otherwise adapted to the particular conditions of the vineyard. Species of grapes vary greatly in their root systems, some having thick, others slender roots; the roots of some are soft, of others hard; some have roots going down deeply, others are almost at the surface of the ground. Manifestly these various root-forms are but adaptations to loose and heavy, dry and moist, deep and shallow soils, or to some circumstance of climate. A vine bruised by adversity is in no condition to withstand phylloxera. Therefore, since the adaptability of a variety to a soil or climate may be changed by the stock, the adaptations of stocks to soils and climates must have attention.
Affinity of stock and cion.
Different varieties of grapes do not behave alike on the same stocks, and different stocks may affect varieties differently. Even when the kinship is close, some grapes resist all the appliances of art to make a successful union; while, on the other hand, quite distinct species often seem foreordained to be joined. For example, Rotundifolia, which has the highest resistance to phylloxera of any species, is useless as a stock because it is impossible to graft any other grape on it, while Vulpina and Rupestris unite readily with varieties of Vinifera, the slight decrease in the vigor of the grafted vines serving oftentimes to increase fruitfulness. Something more is necessary, then, than botanical kinship. Just what is necessary, no one knows, beyond: that there must be conformity in habit between stock and cion; that the two must start in growth at approximately the same time; and that the tissues must be sufficiently alike that there be proper contact in the union. Yet these facts do not sufficiently explain all of the affinities and antipathies which species and varieties of grapes show to each other. Unfortunately, the grape-grower has had but little to guide him in selecting stocks and has had to learn by making repeated trials.
Proper Planting of Grafted Vines
Europeans and Californians long ago learned that failures with grafted vines often came from setting the vines too deep in the soil, the result being that the cions struck root and became independent, whereupon the stock dies or becomes so moribund that the beneficial effects are lost. There are grape-growers who argue that it is beneficial to the vine to have roots from both stock and cion, but experience and experiments very generally teach the contrary, it being found that in most grafts the cion roots grow more vigorously than stock roots and eventually starve out the latter. The disastrous effects of cion-rooting are often to be found, also, when grafting has been done on old vines in the vineyard; and, again, when the graft is too close to the root system.
Another cause of failure is that different stocks require that the vineyard soil be treated differently, especially at planting time. Vulpina stocks require that the soil be much more deeply plowed than for Viniferas on their own roots, since Vulpinas are deep-rooted and are exacting in the depth of root-run required. Those who have had most experience with resistant stocks maintain that all American grapes require rather deeper plowing than European grapes on their own roots.
Influence of the Stocks on the Cion
Up to the present, the growing of grafted grapes has been carried on with little thought of the mutual influence of stock and cion; grapes have been grafted only to secure vines resistant to phylloxera. Yet there can be no doubt that stock and cion react on one another, and that any variety of grapes is influenced for better or worse in characters of vine and fruit by the stock upon which it is grafted. A plant is a delicate mechanism, easily thrown out of gear, and all plants, the grape not the least, are more or less changed in the adjustments of stock and cion. One could fill a large volume on the supposed reciprocal influence of stock and cion in fruits. Space suffices, here, however, to mention only those proved and those having to do with the influence of the stock on the cion when the grape is grafted.
Influence of stocks on European grapes summarized.
Common experience in Europe and California indicates that varieties of Vinifera grapes grafted on resistant stocks which are perfectly adapted to soil and climate produce not only larger crops but sweeter or sourer grapes; that the crop ripens earlier or later; that the vine is often more vigorous; and that there are some minor differences depending on the stock used. Wine-makers assert that the character of their product may be affected for better or worse by the stock. Often vines are so improved by grafting that the extra expense of the operation and of the stock is paid for; although, to be sure, about as often the effects are deleterious. The successes and failures of vineyards on resistant stocks make plain that the vine-grower must study the many problems which stocks present and exercise utmost intelligence in the selection of the proper stock.
Influence of stocks on American grapes.
No doubt American species of grapes may be as profoundly modified by stocks as the European species, but there is but little evidence on this phase of grape-growing to be drawn from the experience of vineyardists. One rather conclusive experiment, however, shows that American grapes may be improved by growing them on stocks which give them better adaptations to their environment. The experiment was tried in the Chautauqua grape-belt in western New York by the New York Agricultural Experiment Station. The test was carried on for eleven years, during which time many interesting possibilities in grafting grapes in this region came to light. It was proved that the stock materially affects the vigor and productiveness of the vine and the quality of the grapes. The following brief account is taken from Bulletin No. 355 of the New York Station:
In this experiment a number of varieties were grafted on St. George, Riparia Gloire and Clevener stocks, and a fourth group on their own roots. The varieties grafted were: Agawam, Barry, Brighton, Brilliant, Campbell Early, Catawba, Concord, Delaware, Goff, Herbert, Iona, Jefferson, Lindley, Mills, Niagara, Regal, Vergennes, Winchell and Worden. The planting plan and all of the vineyard operations were those common in commercial vineyards.
Yearly accounts of the vineyard show that the vines passed through many vicissitudes. The experiment was started in 1902 when St. George and Riparia Gloire stocks from California were set and grafted in the field. Many of these died the first year. The winter of 1903–04 was unusually severe, and many more vines were either killed or so severely injured that they died during the next two years. The vines on St. George, a very deep-rooting grape, withstood the cold best. Fidia, the grape root-worm, was found in the vineyards early in the life of the vines and did much damage in some years. In the years of 1907 and 1909 the crops were ruined by hail.
But despite these serious setbacks it was evident throughout the experiment that the grafted grapes made better vines and were more productive than those on their own roots. As an example of the differences in yield, a summary of the data for 1911 may be given. In this year, an average of all the varieties on own roots yielded at the rate of 4.39 tons to the acre; on St. George, 5.36 tons; on Gloire, 5.32 tons; on Clevener, 5.62 tons. The crops on the grafted vines were increased through the setting of more bunches and the development of larger bunches and berries.
The grapes on the vines grafted on Gloire and Clevener ripened a few days earlier than those on their own roots, while with St. George a few varieties were retarded in ripening. Changing the time of maturity may be very important in grape regions where there is danger of early frost to late-ripening sorts, and where it is often desirable to retard the harvest time of early grapes.
In the behavior of the vines, the results correspond closely with those given for yields. In the growth ratings of varieties on different stocks, the varieties on their own roots were rated in vigor at 40; on St. George, at 63.2; on Gloire, at 65.2; on Clevener, at 67.9. There is no way of deciding how much the thrift of the vines depends on adaptability to soil, and how much on other factors. Since all of the varieties were more productive and vigorous on grafted vines than on their own roots it may be said that a high degree of congeniality exists between the stocks and varieties under test.
The experiment suggests that it would be profitable to grow fancy grapes of American species on grafted vines, and that it is well within the bounds of possibility that main-crop grapes can be grafted profitably. In the general tuning-up of agriculture now in progress, it may be expected that soon American as well as European varieties of grapes will be grown under some conditions and for some purposes on roots other than their own.
Direct Producers
Attempts innumerable have been and are still being made to secure, by hybridizing V. vinifera and American species of grapes, varieties that will resist phylloxera, the mildew and black-rot. The grapes of this continent are relatively immune to all of these troubles, and if hybrids could be obtained to produce directly, without grafting, grapes with the good qualities of the Viniferas—in short, European grapes on American vines—the cultivated grape flora of the whole world might be changed. So far, a "direct producer" that is wholly satisfactory in either Europe or California has not been found for the wine or raisin industries, although a number of varieties are rated as very good table grapes, and a few are used in wine-making. The best of the direct producers are Lenoir, Taylor, Noah, Norton's Virginia, Autuchon, Othello, Catawba, and Delaware.
Plate V.—Vinifera grapes grown out of doors in New York. Top, Malvasia; bottom, Chasselas Golden.