_Characteristics._--The first, or at least the most characteristic signs
of this disease appear especially after a summer rain, or after the
first fall rain. The leaves then become spotted with yellow. The
following season these yellow spots appear as if fused together, and
many leaves become entirely yellow, except the veins, which stand out
bright green. Some leaves are invaded by the yellow from the edges,
while the veins as before remain green. These yellow spots soon turn
brown, the leaves dry up and curl slightly backwards and finally fall
off, leaving the canes bare. During the very first appearance of the
vine plague, many leaves turn brown and dry up in certain spots in the
vineyard without the previous appearance of any yellow spots. The drying
of the leaves proceeds either from the center of the spots, or from the
margin of the leaves, destroying both the leaves and their veins. Later
on in the fall a new crop of leaves appear, but these leaves are small
or very small, bright green and sickly, and do not continue to develop
after they have reached a certain size, different in different vines. In
red varieties of grapes, the yellow spots in the leaves gradually turn
red or claret colored, often resembling the most beautiful autumn
leaves. In districts where the disease is common, these leaves are
generally known as calico leaves on account of their peculiar markings.
The canes do not attain their regular growth, and fail to mature in the
fall, or mature only in spots, the balance of the wood remaining dull
green. The inner parts of the canes are, as a rule, more mature than the
tips. Very often only one or two joints nearest the stem mature, and in
bad cases no part of the canes mature, but at the advent of the rain
turn black and die. Late in the fall the tips of the green canes turn
black, dry up and snap off like glass when touched. The pith turns in
the older canes dark brown, dries up prematurely and dies, while in very
young canes the pith remains watery like a semi-transparent jelly.
Many vines have no mature wood when the leaves have fallen in the
autumn, while others again have some. While the spotted leaves may
appear all over the vineyard, the diseased canes appear on vines in
spots, these spots in the vineyard growing larger year after year. A
dead vine may be seen in the midst of healthy ones, while a healthy
vine, on the other hand, may remain in the midst of dead ones. It takes
generally several years to kill the vines, and some varieties are
hardier than others. Some Muscats may succumb in one year, while some
will last for three years or more. The roots remain alive and healthy
longer than any other part, and, when the top of the vine has already
died, it is common to see the root send up a healthy sucker, which,
however, in its turn, will become diseased and die. It is likely that
the vines in some districts will suffer more than in others, and in
places the vines may not become seriously injured by the disease.
The berries on badly diseased vines do not develop, but shrivel up or
remain sour, and in some cases dry up entirely. In others, again, they
acquire a mawkish taste, lose flavor and sweetness, and make only
inferior or bad raisins. These many different characteristics of the
plague depend evidently on the stage of infection. They do not follow
each other in any certain succession, nor do they all appear on the same
vine. Some vines show one face of the disease, other vines show another,
and the observer must have been previously acquainted with the disease
before he can readily recognize it.
_Nature and Cause._--The cause of the vine plague is not known. No
deadly fungus has so far been found on the vine, nor has any other
deadly parasite been found on the diseased vines. In California the vine
plague has been studied by N. B. Pierce, of the Agricultural Department
at Washington. He suggested once that the disease was of bacterial
nature, but has not proved his theory, his investigations not yet being
finished. Mr. E. Dowlen has also been investigating this disease, and at
one time thought it caused by a fungus, which, however, was proved later
by Dr. H. W. Harkness to belong to the non-injurious kind. No insects of
any kind prey on the vines in sufficient numbers to cause the serious
symptoms of the vine plague.[7] Whatever may be the true cause of the
vine plague, certain it is that it resembles in its advent and spreading
such diseases in men as cholera, yellow fever or the Oriental plague.
The vine plague appears to be especially promoted by warm, moist air and
rain, but it is not confined to damp places, nor has it as yet been
ascertained in what relation it stands to locality and climate.
[7] The most interesting and correct account of the vine plague yet
published is found in an essay on “The Mysterious Vine Disease,” by
Newton B. Pierce, read before the State Horticultural Convention, at
Los Angeles, March, 1890, and published in CALIFORNIA--A JOURNAL OF
RURAL INDUSTRY, May 10, 1890; Vol. 3, No. 18.
In California it first made its general appearance in Anaheim in Orange
county, in the month of August, 1884, when vineyards of old Mission
vines suddenly stopped growing, and the grapes failed to color and
ripen, while many of the vines died the same year. The plague attacks in
preference vines growing on poor, sandy or alkaline soil, or in
vineyards underlaid with hardpan. The weak vines succumb the first of
any. This is the reason why so many vineyardists doubt the existence of
any particular disease, contributing the poor condition of the vineyard
to anything else than the true cause.
N. B. Pierce, who has now spent a year in studying the vine plague, has
found many similarities between it and the _mal nero_ of Italy; but the
descriptions of the foreign investigators are both contradictory and
insufficient, and, without a personal investigation of the Italian or
French vines, the identity of our vine plague with any foreign disease
cannot be established. It is to be hoped that the United States Congress
will make such investigations possible. At present we do not even know
whether the vine plague is original in this country or whether it was
imported from foreign countries. The general opinion in the first
attacked district is that the disease was imported there with grapevines
brought from Europe. So far I have not been able to ascertain when and
by whom such vines were imported, but I am satisfied that in the course
of time it will be found that foreign grapevines were imported to the
vineyards where shortly afterwards this disease first appeared.
_Damages._--The damages caused by the vine plague may be summed up as
follows: The leaves turn spotted and yellow, finally dry up and fall
off. The canes fail to mature, or mature only in spots. Later in the
fall, they die from the tips, which turn black and become brittle. The
berries either dry up or shrivel up, and fail to mature, or at any rate
become mawkish or bitter. The yield becomes less and less every year,
although, the first year that the vines are touched by the disease, the
yield is often unusually large. In severe cases the vine dies in from
one to three years, but a few may linger longer.
_Remedies._--The vine plague has existed in this State for six or eight
years, but as yet few, if any, efforts have been made to extinguish it,
and only during the last year have any experiments been carried on. The
solutions of bluestone and lime which many expected would prove
beneficial to the vines attacked by the plague have, in my opinion, done
little or no good. Spraying the vines when in full foliage with the
I X L compound greatly benefits the vines, and proves a powerful
stimulant and the best remedy yet employed.
LEAF-HOPPER (_Erythroneura comes_).
_Characteristics._--This pernicious little pest is a bug which
multiplies in enormous quantities and sucks the sap out of the vine
leaves. Many use the name of thrips to denote this insect, but this is
incorrect, as the thrips is an entirely different, much smaller, insect,
which so far has never been injurious to the vines of this coast. In
size the leaf-hopper is, at maturity, about one-tenth of an inch. In
color it is yellowish white, with a few red spots. When the insect
approaches maturity, it jumps, but the undeveloped insect or larva only
crawls, principally on the underside of the vine leaves, where their
cast-off skins can be seen in all stages and sizes. The eggs are laid in
the veins of the leaves. The glossy globules which are always seen on
leaves where the leaf-hopper is found are not the eggs, as has been
supposed by many, but is only the vomit which, when irritated, the
hopper throws out either as a defense, or because it desires to rid
itself of an unnecessary burden. The leaf-hopper hatches at least two
times, or possibly three times, during the summer. Many of the insects
remain over during winter time. They feed on almost anything, such as
_alfilerilla_ (_Erodium_), etc., but are especially fond of the
grapevines, and even in the early spring flock onto the young vine
shoots, leaving the less desirable weeds. In some localities this insect
is known variously as the white fly, the vine-hopper, or incorrectly as
the thrips.
_Damages._--The hopper punctures the leaves and causes them to dry up
and fall, thus exposing the grapes to the hot sun. The excrement of the
hoppers also covers the grapes largely, and spoils their appearance and
keeping quality, at least as table grapes. It is principally the table
grapes and wine grapes which are injured by this insect; the former are
made unfit for shipment, and the latter do not color well when deprived
of their leaves. If the grapevines are kept growing, the grapes are less
injured, and some growers even contend that the hopper is advantageous,
as it causes the leaves to fall and the grapes to mature.
_Distribution._--It is not known whether the leaf-hopper is a native of
California, and I hardly believe it is. It does not exist in Southern
California, but in Northern California and in the San Joaquin valley it
is common. In the grape districts of Southern California there is found
another variety of leaf-hopper almost twice the size and of a brilliant
green color, which only once appeared in such quantity as to do any
damage at all. Generally it is quite rare. The _Erythroneura comes_,
however, occurs in countless numbers, and often rises in clouds when the
vines are approached. In some years it is less common than in others,
and after having been plentiful for several years gradually diminishes
in quantity, but never disappears entirely.
_Remedies._--Pasturing the vineyards with sheep as soon as the grapes
are picked is very beneficial. The sheep destroy both hoppers and
leaves, and the following season always finds the hoppers greatly
diminished in numbers. The sheep do no injury to low-pruned vines, and
in Fresno many vineyardists pasture their vines regularly every year in
October and November, or as soon as the grapes are picked and the
vineyards are made accessible.
The gauze bell consists of a bell-shaped cover made of wire netting,
large enough to cover the vine. The inside of the bell is sprayed with
petroleum, and then turned over the vine. A shake is then given the
vine, when many leaf-hoppers will fly up and stick in the petroleum. It
will only pay to use this remedy on table grapes; for raisin grapes it
is too expensive.