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.
[Illustration: 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._
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 pupae and in late June or early July emerge as adult
beetles.
[Illustration: FIG. 37. The grape root-worm.]
[Illustration: FIG. 38. Root-worm beetle.]
The presence of the adult beetles is more easily detected on the
foliage than is that of the larvae 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.
[Illustration: 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 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 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.
[Illustration: 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,
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 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 arsenate 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 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 larvae 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 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 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 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 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._
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.
[Illustration: FIG. 41. First four stages of the grape leaf-hopper.
(Enlarged.)]
[Illustration: 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 pupae to survive.
[Illustration: 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 larvae 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 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 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
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 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 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 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
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 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.
[Illustration: PLATE XVII.--Empire State (x2/3).]
_Black-rot._
[Illustration: 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 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.
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.
[Illustration: 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 "oidium" 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.
[Illustration: PLATE XVIII.--Herbert (x2/3).]