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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.



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.




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.


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.



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.


(Enlarged.)]


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.


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.





Next: Fungous Diseases Of The Grape

Previous: Grape Pests And Their Control



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