Grape anthracnose, or bird's-eye Rot, is widely distributed east of the Rocky Mountains, where at times it is of considerable importance. It was first discovered in central Illinois about 1881 and later was found in many other parts of that state. By 1885 the disease had been noted generally over the eastern and middle - western states. The disease originated in Europe, where it has occurred to a serious extent for many years. The anthracnose fungus was doubtless imported from Europe at some time prior to 1881.
Fortunately the disease does not appreciably affect the Concord, the most extensively-grown of American grape-varieties. Many other favorite varieties, however, are very susceptible to the trouble, especially the Moore's Diamond, Catawba, Salem, Niagara, Diogenes, Brighton, Missouri Reisling, Clinton, Vergennes, Pocklington, Norton, Champion, Thompson's Seedless, Malaga, Tokay and Black Hamburg. On these varieties anthracnose is of considerable economic importance, due in part perhaps to the fact that the disease is not readily controlled. In serious outbreaks the fruit may be almost wholly destroyed, and the vines seriously damaged. The growing of certain desirable varieties in some localities is unprofitable on account of the unusual damage done by anthracnose. It ranks fourth in importance among fungous diseases of the grape east of the Rocky Mountains, Black Rot, Downy Mildew and Powdery Mildew being more troublesome in the order listed.
All green parts of the vine are subject to anthracnose throughout the growing - season. It is most common, however, on the shoots (Fig. 64) and berries (Fig. 65).
On the shoots and tendrils small cankers are produced (Fig. 64). The lesion is brown, slightly depressed in the center, but raised at the border. The spot enlarges, becoming elongate in the direction of the main axis of the shoot. In later stages the center becomes more depressed, and the color turns grayish.
Fig. 64. - Grape anthracnose on Lindley canes.
The bark is finally destroyed, and in severe cases the underlying wood appears burned. Canes are not often girdled, although affected stems bearing clusters suffer in this manner.
On the berries the well-known bird's-eye spots are produced (Fig. 65). The lesions first appear as small, dark-brown areas; later the color is grayish in the center wherever the cuticle is ruptured, but the border remains dark. The spots increase in size, but instead of elongating as they do on the canes, they remain somewhat circular. Between the gray center and the dark border is a well-defined band of bright red. The appearance thus resulting has given rise to the name bird's-eye Rot. Finally the berries wither and dry up, leaving a mummy. Anthrac-nose mummies are not. as extensively wrinkled as Black Rot mummies, and in the former the outline of the originally affected area may still be seen.
Fig. 65. - Grape anthracnose on berries.
In the event that half - grown berries are attacked they become irregular in shape.
The leaves and other parts of the vine when affected by anthracnose show lesions similar to those already described on the shoots. Spots on the foliage are pale-gray with dark - red borders. Cankers are produced on the petioles and veins.
The lesions described above are due to the fungus Glaeo-sporium ampelophagum (= Sphaceloma ampelinum). In America only one spore-stage is known; in France, plant pathologists claim to have discovered a winter sexual spore-stage. Accordingly, the name Manginia ampelinum has been substituted. The similarity of the grape anthracnose fungus to the blackberry and raspberry anthracnose fungus has resulted in one case, at least, in the suggestion of the possible identity of the two organisms.
The mycelium of the fungus grows within the affected tissue. Certain threads come to the surface and form fruiting bodies called acervuli. These structures burst through the skin of berries and canes, sending out many erect conidiophores on which conidia are produced. These spores ooze out in a gelatinous mass held together by their sticky coatings. The sticky substance dissolves in water and the spores are thus liberated. They are disseminated by rain and dew, the process occurring from the time the berry clusters are yet in the bud until the close of the season. Spores falling on green parts of the vine germinate, and after about a week signs of the anthracnose disease begin to appear. The germ - tubes penetrate the healthy, unbroken epidermis. With the advent of the dormant season the fungus apparently ceases activities. It is not definitely known how the fungus passes the winter, but the supposition is that it hibernates as mycelium in lesions on the canes and mummied grapes. In the spring spores from acervuli in the old lesions bring about the first infections.
Moisture and the proper temperature are essential to the development of the pathogene. It is said that a poorly - drained soil also favors the fungus.
Until recently little has been done in American vineyards to prevent anthracnose, although its control is well understood in Europe. Recommendations based on the results of careful experimentation follow: (1) prune out and burn all diseased wood; (2) spray dormant vines with lime sulfur, diluted one to nine; (3) spray the vines with bordeaux mixture, as for Black Rot of grapes as follows: (a) when the shoots are eight to twelve inches in length; (b) just before the flower-buds open; (c) just after the blossoms fall; (d) ten to fourteen days later; (e) and again in ten to fourteen days. The addition of two pounds of resin-fish - oil soap to fifty gallons of the spray mixture in the last two applications is advisable on account of the increased adhesiveness of the fungicide which results.
For the dormant spraying lime sulfur may be replaced by a fungicide of the following formula:
Iron - sulfate, 13 3/4 lb., or 6 7/8 lb.
Sulfuric - acid (commercial) 7 oz., or 3 1/2 oz.
Hot water, 3i gal.
This mixture of iron-sulfate and sulfuric-acid has been successfully applied in Europe. It is objectionable, however, for it is unpleasant to prepare and to use because of the corrosive action of the sulfuric-acid. A four per cent solution of sulfuric - acid has also been used as a substitute for other dormant fungicides.
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