CHAPTER XII
GRAPE PESTS AND THEIR CONTROL
In common with other cultivated fruits, grapes are at the mercy of numerous insect and fungous pests unless man intervenes with remedial or preventive treatment. Happily for viticulture, knowledge of the pests of the vine has made such advancement in recent years that practically all are now controlled by remedial or preventive measures. Possibly no field of agriculture has had greater need, or received greater aid from science in the study and control of insects and diseases than grape-growing. A separate treatise would be required to treat the pathological troubles of the grape fully; only such details of the life histories of the several pests to be discussed as are essential to a proper understanding of the control of the parasites can be given here.
Insect Pests
Insects troubling the grapes are numerous, at least 200 having been described in America, most of which have their habitat on the wild prototypes of the cultivated vines of this continent. For this reason, with a few exceptions, the insect pests of the grape in America are widely distributed, abundant, and, therefore, often very destructive to vineyards unless vigorously combated. The many pestiferous species vary greatly in importance, depending on locality, weather and the variety. Phylloxera, however, the country over, is most common and deserves first attention.
Phylloxera.
This minute sucking insect (Phylloxera vastatrix), injures the grape by feeding on its roots. Decay usually follows its work on the roots and is often more injurious than the harm done directly by the parasite. This decay is always much more serious on European vines than on those of our native species. The phylloxera is a native of the United States east of the Rocky Mountains, from whence it was introduced into France and from France into California, where it causes much greater damage than elsewhere in the United States. Wherever the pest is found, it is more injurious in heavy than in sandy soils. In fact, in very sandy soils the vines are often sufficiently resistant to be practically immune.
Fig. 36. Leaf-galls of the phylloxera.
The life history of the phylloxera is very complex where the different forms of the insect appear and need not be entered into in detail here. East of the Rockies, the most evident indication of the presence of the pest is great numbers of leaf-galls on the under side of the leaves of the grape as shown in [Fig. 36]. These galls, however, are seldom to be seen in California and are not present on Concords and some other varieties in the East. The winter egg may be taken as the beginning of the life cycle of the phylloxera. From a single winter egg a colony may arise, the first insect after hatching making its way to the leaves where it becomes a gall-maker and gives rise to a new generation of egg-laying root-feeders. On varieties and in regions where the gall form is not found, the insect probably goes directly from the winter egg to the roots. Once the pest is established on the roots, generation follows generation throughout the growing period of the vines, as many as seven or eight occurring in one season.
From midsummer until the close of the growing season, some of the eggs deposited by the root-feeders develop into nymphs which acquire wings and emerge from the soil to form new colonies from eggs deposited on the under side of the leaf. An individual insect deposits from three to six eggs of two sizes, from the larger of which come the females and these, after fertilization, move to the rough bark of the vine and deposit the winter egg for the renewal of the cycle.
Several methods of control have been employed in Europe and California, as treatment by carbon bisulfide injected in the soil; flooding in vineyards that can be irrigated; confining the vines to sandy soils; and, most important, planting vines grafted on resistant stocks, there being great variation in immunity of species of American grapes to phylloxera. The subject of stocks resistant to this pest has been discussed in [Chapter IV] and need not be taken up again. East of the Rockies, treatment is not necessary with American grapes.
The grape root-worm.
Fig. 37. The grape root-worm.
The grape root-worm is the most harmful of the insect pests of grapes in the grape-belt along the shores of Lake Erie in Ohio, Pennsylvania and New York. This root-worm ([Fig. 37]) is the larva of a grayish-brown beetle (Fidia viticida), shown in [Fig. 38]. The worms feed at first on the rootlets and later on the bark of the larger roots of the vines so that the injured plants show roots devoid of rootlets and bark channeled by the pest. So plain is the work of the root-worm that the grower never need be at a loss as to the cause of vines injured by this pest. The worms feed during the latter part of the growing season, reaching full growth at this time. The next June they transform into pupæ and in late June or early July emerge as adult beetles.
Fig. 38. Root-worm beetle.
The presence of the adult beetles is more easily detected on the foliage than is that of the larvæ on the roots, for the feeding beetles ravenously devour the upper sides of the leaves, leaving chain-like markings, shown in [Fig. 39], their destructiveness decreasing somewhat after a few days from their first appearance. A fortnight after the beetles begin their attack on the foliage the female begins laying her eggs, to the number of 200, placing them under the rough bark of trunk and cane. These hatch in late July or August and the young grubs at once seek the roots.
Fig. 39. Injuries caused by beetles of the grape root-worm.
Two methods of control have been devised: destruction of the beetles before they lay their eggs; and destruction of the pupæ while in the ground. When the beetles are present in large numbers, many of them may be destroyed by spraying with a mixture of cheap molasses and arsenate of lead, using molasses at the rate of two gallons to a hundred gallons of water and the arsenate of lead at the rate of six pounds. This should be followed by a second spraying a week later, using bordeaux mixture (4–4–50) and three pounds of arsenate of lead. This second spray serves to repel migrating beetles from the vines. The molasses spray is ineffective unless several days of fair weather follow the spraying, as rain washes the material from the foliage. Bordeaux mixture is not easily affected by rain. In moderately infested vineyards, bordeaux mixture and arsenate are used instead of molasses and arsenate of lead, followed in about ten days with a second application of the same material.
An effective method of reducing the number of beetles is the destruction of the pupæ. This is best done by leaving a low ridge of earth under the vines at the last seasonal cultivation to remain until most of the larvæ have pupated, and then be leveled with a horse-hoe and later with a harrow. The horse-hoe and harrow crush many of the pupæ and break the cells of others to the great destruction of the pest. This latter method of control is not adequate in itself and in bad infestations both should be used. When the infestation is only moderate, this latter method is not advised, owing to the lateness of the time of horse-hoeing. It is good horticultural practice to horse-hoe the latter part of May or early June. To wait for the pupal stage of the root-worm delays the work until numerous small roots start which would be destroyed by the horse-hoe. Spraying will control a moderate infestation.
The grape-vine flea-beetle.
Fig. 40. Eggs of grape-vine flea-beetle.
In the warm days of May and June when the buds of grapes are swelling, a shining steel-blue beetle may often be found in the vineyards of eastern America feeding on the tender buds of the grape. From its color the insect is often called the steely-beetle, and from its activity and habit of jumping it is known as the flea-beetle (Haltica chalybea). The vine is seldom seriously injured by this pest but many buds are destroyed, causing the loss of the fruit that should have developed from the buds. It is true that new buds often develop after the injury, but these, as a rule, produce only foliage.
The life history of the flea-beetle is such that the pest is not hard to control, the chief steps in its development being as follows: The beetles deposit small orange-colored eggs, cylindrical in form, illustrated in [Fig. 40], about the buds and in crevices of the bark of the canes in May or June. Most of these eggs are hatched by the middle of June. The larvæ feed upon the foliage until about July first and then crawl to the ground in which they form cells and pupate. The latter part of July the adults emerge and seek wild vines upon which they feed, entering hibernation rather early in the fall. The beetles hibernate under leaves, in rubbish and in the shelter of the bark of trees and vines, but emerge in the warm days the following spring to seek vineyards.
Two methods of control have been developed to keep this pest under. The vines should be sprayed with three pounds of arsenate of lead in fifty gallons of water when the larvæ are feeding on the foliage; or the beetles when feeding may be knocked into a pan containing a shallow layer of kerosene. The former is the cheaper and more effective method provided the grape-grower has the foresight to discover the larvæ, since the larvæ of this summer produce the beetles that will destroy the buds next spring. When the adults migrate from wild vines, or the larvæ were not destroyed in the vineyard, collecting the adults is the only practical method. The destruction of wild vines near a vineyard helps to give immunity from this pest.
The rose-chafer.
The rose-chafer (Macrodactylus subspinosus), a long-legged beetle of a yellowish-brown color, about a third of an inch in length, often appears in vineyards in vast swarms toward the middle of June in northern states and about two weeks earlier in southern states east of the Rocky Mountains. Often they overrun gardens, orchards, vineyards and nurseries, and usually, after having done a vast amount of damage in the month of their devastating presence, the beetles disappear as suddenly as they came. Vineyards on or near sandy soils are most often infested, the larvæ of the beetle seeming to live in considerable numbers only in these light soils. The chief damage to the grape is done to the blossom; in fact the insects, after feeding on the blossoms during the blossoming period, usually migrate to blossoms of any one of several shrubs. The larvæ feed on the roots of grasses, having particular liking for the roots of foxtail, timothy and blue-grass.
Some knowledge of the life history of these beetles is essential to effective control. The beetles emerge as adults in June and after feeding a short time begin to mate, although egg-laying does not take place until the insects have been out for a fortnight or more. The females burrow into the soil and deposit their eggs, seldom more than twenty-five in number, which begin to hatch in about ten days. The young larvæ feed during the remainder of the summer on roots of grasses. They are seldom found deeper than six inches while feeding, but as cold weather approaches they burrow deeper to avoid sudden changes of temperature. The following spring they again come near the surface to feed. The grubs form cells from which the pupæ emerge, as we have seen, about the middle of June, timing their appearance very closely to the blossoming of Concord grapes.
The methods of control are three, namely: destruction of the larvæ; cultivation to kill the pupæ; and spraying to kill the beetles. Since the larvæ feed on the roots of grasses in sandy soils, it is easy to locate the feeding ground of the pest and plant it to cultivated crops which destroy the grasses and therefore the larvæ. The second method of destruction is similar, consisting of cultivation to kill the pupæ. This is accomplished by thorough cultivation during the pupating stage to break the cells and crush the pupæ, thus preventing the emergence of the beetles. The third method, however, is the most effective and consists of spraying the vineyard with a sweetened arsenical spray. The spraying should be done as soon as the beetles appear, using arsenate of lead six pounds, molasses one gallon and water one hundred gallons. It is often necessary to make a second application a week later. If rain occurs within thirty-six hours after spraying, the application should be repeated as soon as the weather clears.
The grape leaf-hopper.
Fig. 41. First four stages of the grape leaf-hopper. (Enlarged.)
From Canada to the Gulf and from the Atlantic to the Pacific, wherever the grape is grown, the small leaf-hopper (Typhlocyba comes) infests the grape in greater or less numbers, feeding on the lower surface of the leaf. Grape-growers commonly call these insects "thrips," a name, however, which really belongs to a very different class of insects. The injury done by this pest varies greatly with the season and the locality, in some regions it being comparatively harmless and in others exceedingly destructive in seasons when it occurs in abundance. There is great variation also in individual vineyards, those near favorable hibernating places and early spring food plants often being injured seriously season after season in succession. These leaf-hoppers obtain their food by piercing the epidermis on the under side of the leaf surface and sucking the sap, and add further injury by inserting their eggs underneath the skin of the leaf. The punctures greatly decrease the starch-producing area of the leaf with the result that the vigor of the plant is lowered, and the quality of the fruit decreased.
Fig. 42. The fifth and the mature stages of the grape leaf-hopper. (Enlarged.)
The life history of the leaf-hopper is very well known. The eggs are deposited in June or early July, and hatch from June 15 to July 10 in New York, the season being earlier or later as one goes south or north. The young leaf-hoppers are wingless, the nymph stage, but reach the adult stage in late July and August, at which time many of them mate, and eggs are laid from which a second brood may develop, although usually only one full brood is produced in a season in the northern states. Figures [41] and [42] show the several life stages of the leaf-hopper. Insects which become adults in the latter part of July feed on the foliage until autumn and then seek winter quarters, passing the winter in the adult stage under fallen leaves, in dead grass or other similar protection. The hibernating place must be dry and for this reason sandy knolls are most favored by the insects. The adults emerge in the warm days of spring and then seek food first on the strawberry, then migrate to red and black raspberries or blackberries, if raspberries are not present. They remain upon these hosts until the grape leaves expand and then migrate to these to feed, lay their eggs and die.
Three methods of control are in use to prevent the ravages of the leaf-hopper: avoiding the planting of raspberries near grapes; spraying with contact insecticides; and the destruction of hibernating places. Since the leaf-hoppers feed especially on the raspberry before the leaves of the grape have expanded in the spring, avoiding planting these two plants near each other is a very effective method of control. The contact spray must touch the body of the insect and must, therefore, be applied before the nymphs develop wings. The best spray is a half pint of Black Leaf 40 to a hundred gallons of water or bordeaux mixture. It is applied to the under side of the foliage by a trailing hose or by an automatic grape leaf-hopper spray devised by F. Z. Hartzell and described in bulletin 344 of the New York Experiment Station. The destruction of hibernating places is almost as effective a method of control as spraying. All weeds and strong-stalked grasses which die in the fall and all rubbish in the vineyard should be destroyed. It is quite worth while, also, to burn leaves and rubbish in fence rows and waste places near infested vineyards in the autumn or early winter. Cover-crops which remain green during the winter do not harbor the leaf-hoppers.
The grape-berry moth.
This pest is widely distributed, attacking the grape wherever grown in North America. The insect feeds on all varieties but is especially destructive to grapes with tender skins and such as grow in compact bunches. Its work is detected usually in compact grape clusters where a number of berries are injured by a "worm." The "worm" is a dark-colored caterpillar, the larva of the grape-berry moth (Polychrosis viteana.) There are two broods of this caterpillar, the first of which feeds on the stems and external portions of the young berries, while the second attacks the berries. The loss to the fruit-grower is of two kinds, the loss of the fruit and the marring of clusters which entails the cost of picking out worthless berries. [Figure 43] shows the work of the grape-berry moth. The damage is usually greatest near woodlands since the trees cause more snow to lodge in the adjoining vineyards, this protection permitting a greater percentage of pupæ to survive.
Fig. 43. A bunch of grapes despoiled by the grape-berry moth.
The moth passes the winter in the pupal state on leaves underneath the vine, emerging about the time grapes are blossoming. The sexes then mate and the eggs are laid on the stems, blossom clusters and newly set fruit. After reaching full growth, the caterpillars cut out a portion of the leaf from which they make a pupal case by means of silken threads, and here pupate for the second brood which emerges in late July and August. Eggs are laid at once and from these come the caterpillars which live entirely in the berry. The larvæ leave the berries about the time the fruit is ripe, form cocoons on the leaves and hibernate. The moths are small, brown in color, mottled with gray and so much the color of the grape cane that they can hardly be detected when resting on the wood.
The grape-berry moth is difficult to control but much can be done to curtail its ravages. Spraying after the fruit sets is the most effective preventive. Bordeaux mixture should be used (4–4–50) to which has been added one and one-half pounds of resin-fish-oil soap and three pounds arsenate of lead. A second application of the same spray is advisable in early August. In a small vineyard or with a slight infestation, it often pays to pick and destroy the berries infested by the spring brood. Plowing infested vineyards in late fall or early spring to bury all leaves prevents the emergence of many of the moths. To be effective, this practice must cover the leaves deeply directly under the vines and this earth must remain until after the time for the adults to emerge. Plowing under leaves is not as effective on sandy as on heavy soils, since sandy soils do not become sufficiently compact to prevent the escape of moths.
Insect pests of minor importance.
Of the 200 species of insects that feed more or less on the grape, entomologists mention several others than those described that in occasional years or localities become abundant and cause serious injury. Thus, there are several species of cut-worms which sometimes feed on the expanding buds of the young leaves of grapes. The damage of these cut-worms to the grape is greater in California than in other parts of the United States, but nevertheless they occasionally feed on the vines in eastern regions to the detriment of the crop. The most satisfactory control measure for cut-worms is the application of poisoned bait placed on the ground at the base of the vines.
In California there is a grape root-worm (Adoxus obscurus) quite distinct from the grape root-worm of eastern America which injures both the roots and the parts of the vine above ground. As in the eastern species, the best evidence of infestation of this pest is the narrow chain-like strips eaten out of the leaves, though the insect also gouges out part of the petioles, pedicels, berries and shoots and works under ground, eating the rootlets and bark of the larger roots. Infested vines show a stunted condition, the canes fail to attain a normal growth and often the vines are killed outright. As in the case of the eastern species, this root-worm is the larva of a beetle, the life history of the insect not being greatly different from that of the eastern beetle. Two methods of control are fairly effective: the adult beetles may be jarred from the vine and captured on a screen when the infestation is restricted to small areas; or the beetles may be poisoned with the arsenical spray recommended for the eastern species. Both jarring and spraying often have to be repeated as new infestations appear.
The grape leaf-folder (Desmia funeralis) is another insect pest of vineyards in California, and occasionally in the East, which works, however, only in restricted localities and in occasional years. In California, the insects are detected in a vineyard by the characteristic rolling of the leaves in which a tube rather less than the diameter of a lead pencil is formed for the home of the larvæ. The larvæ feed on the free edge of the leaf in the interior of the roll and are thus protected by the outer layers. In the East the caterpillar merely folds the edges of the leaves together. This leaf-folder hibernates as a chrysalis, coming forth in early spring to lay eggs on the vine shortly after the foliage has appeared. There are two broods in California and the northern states and three broods in the southern states. The leaf-folder is easily disposed of by spraying with an arsenical spray just after the eggs hatch and before the larva is protected by its roll of leaves.
Still another pest found throughout the United States and especially destructive in California is the hawk-moth (Pholus achemon), the larvæ of which occasionally do serious damage to small areas of vines. These larvæ are very similar to the large worms, familiar to all, which attack the tomato and tobacco. The insect hibernates in the pupal state in the ground where it may be distinguished as a large cylindrical object of dark brown color. The moths emerge about the middle of May and deposit their eggs on the leaves of the grape, upon which the larvæ when hatched immediately begin to feed. There are several species of these hawk-moths, all of which have essentially the same life history. It is not a difficult pest to control since the larvæ are easily killed with arsenical sprays; or if there are but occasional specimens they may be picked by hand. There are several species of the hawk-moth which attack the grape but this is the common one.
In eastern grape-growing regions, there are two other destructive grape insects widely distributed, but each noteworthy as pests only in the Appalachian region of West Virginia and neighboring states. One is the grape-curculio (Craponius inæqualis), not essentially different from the familiar curculio of the plum and cherry. This snout-beetle feeds freely on the upper surface of the leaves and the bark of fruit stems, and the female in laying eggs devours the tissues of the grapes in excavating her egg chamber. The grape-curculio is effectively destroyed by spraying with an arsenical spray in the spring as the beetles appear on the vines and before egg-laying begins.
Another insect pest of this region is the grape-vine root-borer (Memythrus polistiformis) closely allied to the peach-borer, known by all fruit-growers and the squash-vine borer known to the growers of vegetables. This borer is the larva of a moth and is a whitish grub with a brown head which, when fully grown, is about one and three-quarters inches in length. The body is slender, distinctly segmented and has a sparse covering of short, stiff hairs. These larvæ burrow into the grape-root, at first confining themselves to the softer portions of the bark, often encircling the root several times, but later bore with the grain of the wood and by the end of the season so destroy the roots as to leave only the thin membrane of the outer bark intact. This pest is difficult to deal with. The borers cannot be removed by "worming" as in the peach, and neither can the roots be protected by sprays or washes. No one variety of the grape seems more immune than another. Thorough cultivation in the months of June and July to destroy the insects while in their cocoons at the surface of the ground seems to be the only method of stopping their ravages, and this is not always effective.
Fungous Diseases of the Grape
The grape is ravaged by four or five fungous diseases in America, unless the utmost vigilance is exercised to keep the parasites in check. Happily for commercial viticulture, there are regions, as we have seen in the description of grape regions in [Chapter I], so fortunate in their freedom from fungous diseases that there is little uncertainty in grape-growing and but small expense in controlling diseases. Also modern science has discovered the life history of all the important diseases and devised fairly effective means of combating them.
All of the fungous parasites of the grape in America are indigenous, having long subsisted on wild vines. They are, therefore, all widely distributed, and as cultivation has presented to them great numbers of grape plants in continuous areas, the diseases have increased rapidly in intensity, at times have swept like wildfire through grape regions devastating and utterly ruining great areas of vines. Means, however, are now at hand in remedial and preventive treatment, which, while because of cost may not permit the grapes to be grown profitably in all parts of America, do permit their culture for home use in practically all agricultural districts in the country.
Plate XVII.—Empire State (×2/3).
Black-rot.
This is the most widely distributed and the most destructive fungous disease of the grape in the region east of the Rocky Mountains. Fortunately, it is unknown on the Pacific coast. The disease is caused by a parasitic fungus (Guignardia Bidwellii) which gains entrance to the grape plant by means of minute spores distributed chiefly by wind and rain. Black-rot passes the winter in mummied grapes, on dead tendrils or on small, dead areas on the canes. In the spring, the fungus spreads from these spots to the leaves and forms brown leaf spots about a fourth of an inch in diameter, or oblong, black spots on the shoots, leaves, petioles and tendrils. Later the disease spreads to the fruits, not usually attracting attention until the berries are at least half grown. Soon after the ravages of the fungus become apparent on the berries, the fruits turn black, shrivel and become covered with minute black pustules which contain the summer-spores. [Figure 44] shows the work of black-rot. In the winter and spring, another form called the winter- or resting-spore is produced upon these old, shriveled, mummied berries, and these carry the disease over from one season to another.
Fig. 44. Work of black-rot of the grape.
Since the disease is carried through the winter in mummied fruits and diseased wood, the desirability of destroying these mummied grapes and the leaves and prunings of infected vines as soon as possible is apparent. This treatment, however, is not sufficient, and the disease can be effectually controlled only by thorough spraying with bordeaux mixture (4–4–50). The first application should be made just before the grape blossoms; the second, shortly after blossoming. The amount of material applied matters less than evenness in distribution and fineness of the spray as applied. In rainy seasons, perhaps a third or a fourth application should be made in regions where the disease is serious; the third is made when the berries are the size of a pea; the fourth, as the berries become large enough to touch each other.
Downy-mildew.
Downy-mildew (Plasmopara viticola) rivals black-rot for first place among fungous diseases of the grape. It is found in all grape regions east of the Rocky Mountains but does most harm in northern localities. Like black-rot, downy-mildew attacks all the tender growing parts of the vine, but is chiefly found on the foliage and is usually less destructive than black-rot. As first seen on the foliage, the work of the fungus appears as greenish-yellow, irregular spots upon the upper surface which later become reddish-brown. At the same time on the under surface of the leaf, a thin, white downy growth puts forth. The spores of the fungus are produced on this downy growth, and under favorable conditions are distributed by wind and water to all tender parts of the vine, where they germinate and begin their work of destruction. The fruit is attacked when partly grown, as shown in [Fig. 45], becoming covered with the gray down of the fungus, the "gray-rot" of the grape-grower. If the berries escape the disease until half grown, the fungus causes a brownish-purple spot that soon covers the whole grape, giving the disease at this stage the name of "brown-rot." Besides the summer-spores, another form of reproductive bodies is produced in the winter to carry the fungus through the resting period.
Fig. 45. Grapes attacked by downy-mildew.
Downy-mildew, like black-rot, spreads most rapidly and does most injury in hot, wet weather. As with practically all diseases of the grape, much can be accomplished in the way of control of the disease by destroying infested leaves, shoots and berries which contain the winter spores, but these sanitary measures are not sufficiently effective and vineyards must be sprayed as recommended for black-rot, except that the first application should be made before the blossom-buds appear.
Powdery-mildew.
Less troublesome than downy-mildew in the East, powdery-mildew (Uncinula necator), unless checked, is capable of destroying the entire crop of European grapes on the Pacific slope. In the East it sometimes causes great loss on the several varieties known as "Rogers hybrids" and, curiously enough, is often a rather serious disease of the Concord. The disease is caused by a superficial fungus which passes the winter on fallen leaves and also on the canes. The spores begin to germinate a few weeks after the grape blossoms, but the disease is not often found until the grapes are nearly half grown. The fine white filaments of the fungus, which constitute the vegetative portion of the parasite, then attack the leaves, shoots and fruit, sending up short irregular branches on which great numbers of spores are borne. These give the upper surface of the leaf a gray, powdery appearance, hence the name. Eventually the diseased leaves become light brown and if the disease is severe, soon fall. Infected berries take on a gray, scurfy appearance, speckled with brown, are checked in growth and often burst on one side, exposing the seeds. The berries, however, do not become soft and shrunken as when attacked by the downy-mildew. The disease passes the winter in resting-spores produced late in the growing season. Powdery-mildew differs from other fungous diseases of the grape in being more prevalent in hot, dry seasons than in cold, wet ones.
In eastern America powdery-mildew is controlled by the treatment recommended for black-rot. When black-rot is not prevalent, two sprays with bordeaux mixture are recommended; the first in early July and the second about two weeks later. On the Pacific coast, however, powdery-mildew or "oïdium" as it is often called there, the name coming from Europe, is more cheaply and more successfully combated by dusting with flowers of sulfur. Dusting is often done by hand or with perforated cans but this is wasteful and uncertain, and any one of several sulfur-sprayers may be used which does the work better.
Anthracnose.
Another widespread disease is anthracnose (Sphaceloma ampelinum), called "birds-eye-rot" because of the peculiar spots produced on the affected fruits, which attacks leaves, shoots and fruits of the vine. It first appears on the leaves in small, irregular, dark brown sunken spots with a dark margin. Later it appears on the fruits, having much the same appearance though the spots are usually larger and more sunken, the disease being most characteristic on the fruit, however. Frequently two or more spots unite and so cover the greater part of the berry. The fruits become hard, more or less wrinkled, and the diseased area often ruptures, exposing the seed, much as with powdery-mildew. The spores of the fungus are produced in great numbers on diseased areas during the growing season and are borne on thread-like filaments which live throughout the winter in the tissues of the vine and are ready for new growth in the spring. Winter-spores have not yet been discovered.
Anthracnose is widely distributed in eastern America but seldom causes great or general loss, most of the commercial grapes being relatively immune to the disease. A few sorts rather commonly grown in home vineyards, as Diamond, Brighton and Agawam, suffer most from anthracnose. Spraying with bordeaux mixture, as recommended for black-rot, is usually sufficient to keep the disease in check.
Dead-arm disease.
A troublesome disease of recent appearance is now doing considerable damage in the Chautauqua grape-belt along the shores of Lake Erie, being most common on the Concord. From the fact that it is usually found on one arm of the vine it is called "dead-arm disease" (Cryptosporella viticola.) The disease is caused by a fungus which passes the winter in small, black fruiting bodies in the dead parts of the vine. Early in the spring the fungus spreads by means of spores to the young shoots and later in the season attacks mature berries, producing small, black, oblong spots of black-rot. Sooner or later, if the diseased shoot is not cut off, the fungus spreads to the arms or trunk of the vine, producing a slow, dry rot which eventually kills the affected part. Fortunately, the presence of the disease is quickly detected by small yellowish leaves, much crimped about the margin.
The fungus is easily controlled by marking the diseased arms when the first symptoms appear and cutting these off at pruning time. If the vine is much mutilated by such pruning, usually suckers can be brought up from beneath the surface of the ground to renew the vine. The applications of bordeaux mixture recommended for black-rot are valuable in preventing the dead-arm disease. The disease is largely prevented by renewing the old wood of the vine as soon as the trunk begins to show a gnarled appearance.
Shelling.
In eastern America, especially in the Chautauqua grape-belt, grape-growers not infrequently lose a large part of the crop by the premature falling of the grapes from the stems. The trouble is an ancient one and is designated as "shelling" or "rattling." This premature dropping usually begins at the end of a cluster, and clusters farthest from the trunk are earliest affected. When vineyards suffer badly from this shelling, the vines often take on a sickly appearance, the foliage falling off in color and the outer margins of the leaves drying up more or less. The fallen fruit has an insipid taste and is, of course, worthless even if it could be harvested.
The cause of the trouble is not known. Grapes may "rattle" on high land or low land, on poor soil or rich soil, on heavy or light soil. A vineyard may be affected one year and not the next. Grape-growers usually attribute the trouble to faulty nutrition, but applications of fertilizers have not proved a preventive. Old and well-established vineyards seem freer from the trouble than new and poorly established plantings. The most reasonable theory as to the cause of shelling is that it comes from faulty nutrition of the vine, but the conditions so affecting the nutrition are not yet satisfactorily determined.
Diseases of minor importance.
Ripe-rot or bitter-rot (Glomerella rufomaculans) is a disease due to the same fungus causing the bitter-rot of the apple. As the name indicates, the disease usually appears on the fruit at ripening time and under favorable conditions continues after the grapes are picked. It may also attack the leaves and stems. The first indication of the fungus is the appearance of reddish-brown spots which spread and eventually cover the whole fruit. The berries do not shrivel, but the rotted surface becomes dotted with pustules in which the spores are borne. It is hard to tell how much damage this disease does, but it is not usually great and the late applications of bordeaux mixture for black-rot or powdery-mildew are very effective in controlling it.
Crown-gall, now known to be a bacterial disease which causes knots or galls on the roots of various wild and cultivated plants, sometimes attacks grape roots or even the vines above ground. Occasionally, the disease is rather serious, but it is not often to be reckoned with in the vineyard regions of America. Fungicides are useless in combating the disease and all that can be done is to exercise great care in planting infected stock. It is doubtful whether crown-gall ever seriously injures vines in northern regions, although it may occasionally do so in the South.
In California there is a somewhat mysterious disease known as "Anaheim disease," because of its having first made its appearance in the vicinity of Anaheim. As near as can be learned, the disease first appeared in 1884 and then spread rapidly from forty to fifty miles from the point where it began its ravages, causing direct and indirect loss of many millions of dollars, and leading to the abandonment of grape-growing in some parts of southern California. Fortunately, in recent years the Anaheim disease is less aggressive but still does more or less damage. The nature and the treatment of this disease are not as yet fully determined, although several experimenters are studying the trouble. Californians whose vineyards suffer from this disease should apply to the experiment station at Berkeley for the latest information in regard to it.
Coulure is another trouble of the vine in California of which little is yet known, either as to cause or treatment. The term signifies the failure of the fruit to set or to remain on the clusters. The trouble occurs in varying degrees from the loss of a few berries to the complete shelling of the fruit from the stem. It is worse in some localities than others and in some varieties than others. Various causes have been assigned to the disease, chief of which, and most probable, are unfavorable climatic conditions.
Control of Insects and Diseases
From the number of insects and diseases found on the grape, it would seem that, literally, "pestilence walketh in darkness and destruction wasteth at noonday" in the vineyards of the country. But not many of the ills that grape-flesh is heir to are ever found in one region, and the vineyard is seldom attacked by many diseases or insects in a single season. There was a time, as we have said before, when grape-growers were so beset by pests which they could not control, that viticulture was one of the most uncertain fields in agriculture. But one brilliant discovery after another has brought the pests of the grape under the hand of man until now there are but few that need cause much expense in treatment or worry as to the outcome.
Plants cannot be attacked by diseases unless infection is permitted. It follows that by proper sanitation most of the insect pests of the vine can be kept out of the vineyard.
Vineyard sanitation.
By changing or modifying environment, immunity can be secured from many of the pests of the grape and damage may be reduced with most if not all. Cultivation, as has been noted under several insect pests and one or two of the diseases of the grape, is an effective method of eliminating grape pests. In the case of insects, it destroys the insects themselves and the hibernating places as well. The vineyard should never be kept in sod, but always under thorough and frequent cultivation. Vineyard sanitation is greatly improved, also, if cover-crops which remain green during the winter are planted after the last cultivation. Cultivation should usually be preceded by deep plowing in the fall or spring to turn under fallen leaves and weeds or grass in which hibernating insects may pass the winter.
The surroundings of the vineyard should be looked after. Fence-rows and waste lands which cannot be cultivated may often be burned over to destroy the hibernating places of grape insects. As a rule, it is unwise to plant the bramble berries or even strawberries in vineyards, or adjoining vineyards, since these plants afford hibernating places and food plants for some of the grape insects, especially the destructive leaf-hopper. Lastly, precaution should be taken by destroying all wild grape-vines near vineyards, as these frequently harbor insects and diseases, the flea-beetle finding the wild grape-vine almost a necessity to its existence.
Spraying.
Definite rules cannot be laid down for spraying vineyards the country over. The literature on this subject is plentiful in any state in which grapes are largely grown, within the reach of the grape-grower, and is not difficult to understand once it is in hand. Every grape-grower should secure and study the publications of the state experiment stations having to do with the control of insects and diseases.
The number of applications and the sprays to be used vary greatly in different parts of America. On the Pacific slope the only application yearly required in most vineyard regions is dusting with flowers of sulfur for powdery-mildew. Several other pests may, however, from year to year, or in one locality or another, require special treatment. In the grape regions of New York, many grape-growers do not spray at all, but these are usually slovens or procrastinators whose profits are small and uncertain. In the grape regions of the northeastern states, orderly vineyardists spray at least once with bordeaux mixture (4–4–50) in which is put three pounds of arsenate of lead, no matter how few insects and fungi are present. This treatment is given soon after the blossoms fall. In more southern regions it may be necessary to make a similar treatment soon after the first leaves appear, again after the blossoms fall and every two weeks thereafter until the grapes begin to turn in color, making as many as four, five or even six applications in all. To these regular applications of bordeaux mixture and arsenate of lead, contact insecticides, as some of the nicotine preparations, may have to be added; or, for special purposes as specified in discussing the several pests, cheap molasses is added. It is doubtful, however, whether the grape can be grown with commercial success where insects and fungi prevail and are so pestiferous as to require annually more than two or three applications of spraying mixtures.
Plate XVIII.—Herbert (×2/3).