[Ill.u.s.tration: 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 pupae 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 mola.s.ses and a.r.s.enate of lead, using mola.s.ses at the rate of two gallons to a hundred gallons of water and the a.r.s.enate 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 a.r.s.enate of lead.

This second spray serves to repel migrating beetles from the vines.

The mola.s.ses 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 a.r.s.enate are used instead of mola.s.ses and a.r.s.enate 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 pupae. 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 larvae have pupated, and then be leveled with a horse-hoe and later with a harrow. The horse-hoe and harrow crush many of the pupae 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._

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.

[Ill.u.s.tration: FIG. 40. Eggs of grape-vine flea-beetle.]

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, ill.u.s.trated 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 larvae 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 a.r.s.enate of lead in fifty gallons of water when the larvae 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 larvae, since the larvae of this summer produce the beetles that will destroy the buds next spring. When the adults migrate from wild vines, or the larvae 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 larvae 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 larvae feed on the roots of gra.s.ses, having particular liking for the roots of foxtail, timothy and blue-gra.s.s.

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 larvae feed during the remainder of the summer on roots of gra.s.ses. 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 pupae 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 larvae; cultivation to kill the pupae; and spraying to kill the beetles. Since the larvae feed on the roots of gra.s.ses in sandy soils, it is easy to locate the feeding ground of the pest and plant it to cultivated crops which destroy the gra.s.ses and therefore the larvae. The second method of destruction is similar, consisting of cultivation to kill the pupae.

This is accomplished by thorough cultivation during the pupating stage to break the cells and crush the pupae, thus preventing the emergence of the beetles. The third method, however, is the most effective and consists of spraying the vineyard with a sweetened a.r.s.enical spray.

The spraying should be done as soon as the beetles appear, using a.r.s.enate of lead six pounds, mola.s.ses 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._

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 cla.s.s 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.

[Ill.u.s.tration: FIG. 41. First four stages of the grape leaf-hopper.

(Enlarged.)]

[Ill.u.s.tration: 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, pa.s.sing the winter in the adult stage under fallen leaves, in dead gra.s.s 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 gra.s.ses 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 cl.u.s.ters 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 cl.u.s.ters 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 pupae to survive.

[Ill.u.s.tration: FIG. 43. A bunch of grapes despoiled by the grape-berry moth.]

The moth pa.s.ses the winter in the pupal state on leaves underneath the vine, emerging about the time grapes are blossoming. The s.e.xes then mate and the eggs are laid on the stems, blossom cl.u.s.ters 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 larvae leave the berries about the time the fruit is ripe, form coc.o.o.ns 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 a.r.s.enate 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 a.r.s.enical 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 larvae. The larvae 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 a.r.s.enical 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 larvae of which occasionally do serious damage to small areas of vines.

These larvae 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 larvae 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 larvae are easily killed with a.r.s.enical 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 (_c.r.a.ponius inaequalis_), 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 a.r.s.enical 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 spa.r.s.e covering of short, stiff hairs. These larvae 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 coc.o.o.ns 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.

[Ill.u.s.tration: PLATE XVII.--Empire State (2/3).]

_Black-rot._

[Ill.u.s.tration: FIG. 44. Work of black-rot of the grape.]

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 pa.s.ses 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.

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.