WHY AND WHEN WINTER KILLS GRAPES.* Necessity for F. H. HALL. "For every evil under the sun, The winter killing of fruits is an evil for which a remedy would be heartily welcomed; but effective control of winter's rigors or prevention of their investigation. dire consequences has seemed to many investigators so "impossible" as hardly to be worth study. Recent experiments with Vinifera grapes at the Station have shown, however, that winter injury, one of the great obstacles to success with these grapes in early attempts to grow them, can be easily controlled. Can like effective, practicable methods of preventing the occasional disastrous freezing of fruit buds or fruiting canes of American grapes be developed? As experience has often shown, the best "striving" for a remedy for any evil is a thoro investigation of the conditions under which it develops and of the causes which produce it. The occurrence of three years of marked shortage of crops in the "Grape Belt," due to winter injury, has given opportunity for such study of the factors influencing winter killing; and the results of these investigations are presented in detail in the bulletin of which this "Popular Edition" is a condensation. Years of grape shortage. The grape crop of 1910 in the section about Fredonia, particularly in the Station vineyard there, showed that more than half of the fruit buds were killed during the previous winter; again in 1913, the yield dropped to about half what it was in 1912 or 1914; and in 1916 the tonnage was the lowest known for many years. While each of these low-yield crops was preceded by notably cold weather during the preceding winter, it was not low temperatures alone that determined the injury, nor was the extent of injury in the three seasons measured by the fall of the mercury. The half crop of 1910 followed a winter when the lowest reading of the thermometer was -10° (in February); yet the crop of 1912 was practically uninjured by the winter altho Low temperature alone not responsible. p. 586. * Reprint of Popular Edition of Bulletin No. 433, April, 1917; for Bulletin see [Plates LV and LVI illustrated this text ] the mercury dropped to -19° on February 10th of that year. Similarly, the crops of 1914, preceded by a thermometer reading of -15° in February, was twice as large as that of 1913, when the lowest temperature recorded for the winter was only 0° or slightly below. The abnormally low temperature of -16° in mid-March of 1916 would indoubtedly have caused a poor crop in the fall of that year, but other factors were necessary to bring the yield down to one-third of what the vineyard had produced. Lack of maturity leads to dead buds. Undoubtedly the most important factor in winter injury to grapes is immaturity of tissues in the fall. Preceding the severe injury in the winter of 1909-10 was a marked shortening of the season of growth, so that fruiting wood and buds went into the dormant condition soft and moist. On October 12 and 13, toward the close of the harvest of 1909 and while many grapes were still on the vines, a freeze stopped growth so that the tissues had no further opportunity to ripen and harden. Of course, the drop to 27° at this time did not actually kill buds or wood on which the next season's crop depended; but their immaturity allowed them to succumb easily at one or more of three critical times during the winter. These were a long-continued period of cold weather in December with 5° as a minimum, a sudden drop to -10° in late February, and a freeze in late April (27°) following an abnormally warm period when buds probably started growth. In 1912 very heavy rainfall in September with temperatures far above the normal promoted succulent growth and again led to immature wood and improperly ripened buds. In pruning during this fall it was impossible to find enough well-matured canes on twoyear wood to provide for a full setting of fruit, and it was necessary to use some canes coming from older wood. Only three-fourths as much wood was pruned away this fall as in the previous year, owing to the light weight of the withered, immature canes, yet fewer buds were left for fruiting than in that year. Altho no remarkably low temperatures were recorded for the winter of 1912-13 the poorlymatured canes and buds again suffered, so that the crop was only a little larger than that of 1910. In the late summer of 1915 low temperatures and cloudy weather made growth of fruit and wood slow; and again a warm, rainy September and a cool, dark October left wood soft and succulent, so that it was in no condition to resist the low temperatures of February (-13°) and March (—16°) that followed. Frequently light crops follow heavy ones in vineSome yards, the common assumption being that the heavy winter killing crop exhausts the vine's supply of food, which it overlooked. must have an "off year" to replenish. This is undoubtedly true to some extent, but winter killing of part of the buds also enters here as a factor. The energies of the vine are probably devoted mainly to ripening the fruit as long as this remains immature on the plant, leaving the final maturing of buds and canes to the comparatively short period which comes between the grape harvest and stoppage of growth by cold. With a large crop, too little strength remains in the vine to mature the buds properly, and many of them are killed or changed in character by winter without general death of the canes. The bud of the grape is compound, consisting freGrape buds quently of three buds enclosed within the same bud compound. scales: The first, or primary, to produce fruit; a secondary which ordinarily produces wood only, but may sometimes bear fruit; and a tertiary, which ordinarily remains undeveloped, but expands as a shoot in case the others are destroyed. The unnoticed winter killing may cause the primary bud to fail, when the secondary, or even the tertiary bud, puts forth a shoot; and the owner of the vineyard thinks the vine did not produce a fruit bud at all, because of food exhaustion. Many instances of this character have been observed in the studies at Fredonia; and, on the contrary, it has also been noted that two full crops may succeed each other, like those of 1911 and 1912, when winter killing did not harm the second crop because conditions allowed proper maturity of both fruit and wood in 1911. Varieties differ in resistance to cold. The winter killing of the season of 1915-16 showed that varieties differ greatly in their resistance to winter injury. The destruction of buds in the Station vineyard at Fredonia varied from 10 per ct. to 100 per ct., or complete killing. This vineyard contained about 150 varieties or representatives of species; and of these twenty lost more than 80 per ct. of their buds, and fifteen of them lost less than 20 per ct. These varietal differences indicate, to some extent, that hardiness to winter injury is a species characteristic, though species are so thoroughly intermingled in many varieties that very definite conclusions are not warranted. Labrusca influence definitely lessens the tendency to such harm; while varieties with Vinifera blood, any combination, usually show a high percentage of winter injury. Aestivalis varieties appear slightly less affected, and Riparia still less but more than the relatively hardy Labrusca crosses. in This specific difference in groups of varieties may be associated with greater or less hardness of wood, since grapes are known to differ considerably in this respect, but studies have not been carried far enough to establish this correlation. Index to maturity. In nearly all the cases studied, immaturity of wood and buds for the season was indicated by immaturity of the fruit, as shown by high acidity and low content of solids, especially sugar. The poor crop of 1910 followed that of 1909 with less than 16 per ct. of sugar, that of 1913 was prophesied by a sugar content of only 14 1/6 per ct. in the crop of 1912, and that of 1916 by 1915's sour fruit with only 14 per ct. of sugar. The good yields of 1911, 1912, 1914 and 1915 were preceded by crops with sugar approaching 17 or 18 per ct. This index cannot be taken as infallible, however, since many other factors than maturity of wood and bud may influence the degree of winter killing. Most perfect maturity may be followed by winter injury, if warm and cold periods alternate too violently or too frequently; but such maturity undoubtedly serves as a protection in ordinary winter weather. Other factors considered. Since immaturity predisposes to winter injury, those factors which tend to produce slow growth or to prolong unduly the season of growth are accessories before the fact" of winter killing. Among the factors found to exert such an influence, improper drainage was perhaps most injurious. In some instances, severe pruning after damage by late frosts in the spring induced rank growth of wood, which did not properly mature and therefore suffered during the following winter. Excellent opportunity was given to test the effect of fertilizer elements on maturity, since the Station vineyard contains duplicate plats fertilized with these elements alone and in combination with each other and with lime. None of the elements nitrogen, phosphorus and potash influenced maturity; so none of them can be considered as having any relation to winter injury of grapes. Winter injury in very unfavorable seasons cannot be Conclusions. prevented, of course; but the evidence indicates that something can be done to lessen the amount of damage in such years and to reduce it to a minimum in other years. First, vineyards should not be located on land that cannot be readily drained; and drainage systems should be installed or improved, where possible, in vineyards already established. Second, the time of discontinuance of vineyard cultivation in mid-summer or later should be governed by the weather, allowing cover crops or weeds to grow longer if soil is full of moisture, so that the transpiration of these plants may lessen water in soil and check undue luxuriance of the grape vines. Wide-leaved covercrops, or green-manuring crops, like rape and cowhorn turnips, may shade the ground so much, however, that the check of evaporation from the soil surface is more detrimental than the transpiration from the plants is helpful. Thin seeding is the remedy where such conditions are anticipated. Narrow-leaved plants like the grains, or sparse-foliaged crops like buckwheat, exert comparatively little shading effect. Slowly available forms of nitrogen, such as raw bone, leather scrap, hair, etc., should be avoided unless used very early, so that their stimulus to growth may not come so late that the wood is left immature. POOR VENTILATION INJURES STORED POTATOES.* F. H. HALL. A few years ago a diseased or abnormal condition Blackheart of shipped potatoes was found to be due to overnot always heating during a delay in transit. The centers due to of the potatoes became deep brown or black, so overheating. the name "blackheart" was applied to the trouble. Bartholomew, the investigator of this condition, found that, to avoid danger of frost when the shipped potatoes were delayed, the car had been heated excessively; and he was subsequently able to reproduce the blackening of the potato flesh by subjecting the tubers to temperatures from 100° to 113° F. He gave, as a secondary cause that might produce or intensify the trouble, lack of oxygen from insufficient ventilation. It was accidentally found at this Station that potatoes allowed to receive only small quantities of air showed the same appearance, tho exposed only to temperatures far below those mentioned by Bartholomew. Extensive and long continued series of experiments begun by the Station botanists in consequence of this discovery have proved that poor ventilation, even when temperature conditions are normal, may lead to serious injury from blackheart. This fact has a very important bearing on the problem of proper storage for potatoes. In the earlier Station experiments jars were used. Experiments Weighed quantities of clean, dry tubers were placed. with tubers in the jars with known proportions of air and .in jars. the jars hermetically sealed. Different lots of these were kept for varied periods of time at temperatures within and above the range of those occurring in storage, extending to 70° F. These tests proved conclusively that potatoes can not long stand close confinement with limited quantities of air. The lower the * Reprint of Popular Edition of Bulletin No. 436, July, 1917; for Bulletin see p. 277.] [Plates X, XI, XVII and XVIII illustrated this text.] |