POWDERY MILDEW OR UNCINULA.

General Notes.

—This disease of the grapevine is caused by the growth of parasitic fungus known in Europe as Oidium Tuckeri, and in this country as Uncinula spiralis or powdery mildew. I am satisfied the two names signify the same fungus, only the European form has never been found as highly developed as the American one, which has on that account received a name of its own. If the two are identical, then the European Oidium, which for many years caused the destruction of the transatlantic vineyards, was imported to that country from this. The Uncinula spiralis is undoubtedly native on our indigenous vines.

Characteristics.

—The mildew appears in two different stages, one in the spring when the vines are in blossom, the other again later in the summer when the fruit is more advanced. The first stage of the mildew resembles a fine cobweb spun between the flowers of the bunch. If allowed unrestricted sway, the flowers will drop off, the fruit will never set, or set only imperfectly, and the crop will be a great loss or even a total failure. Generally the inexperienced vineyardist does not perceive the mildew until too late. A slight touch to the vine will then bring down all the young fruit or blossoms like a shower, and the stem of the bunch will be seen to be entirely bare, or with only a few scattered berries. This form of the Uncinula mildew has not been as scientifically investigated as would be desirable, and nothing is known as regards its development. It is possibly a primary generation and early stage of the later Uncinula. I believe this form of the mildew is identical with the disease which is called Colure by the French, and which is characterized by the dropping of the young, undeveloped grapes. The first appearance of this mildew is always accompanied by white, salty excrescences on the edges of the grape leaves. Whether they are directly or indirectly connected with the fungus is not known.

The later form, the powdery mildew, and the form which has given this mildew its name, appears later in the season, when the grapes are half grown or more. It then takes the shape of fine powder-like patches or blotches on the upper side of the leaves, stems or berries. These spots are of a dull gray or whitish gray color, and smell strongly of mold or mushrooms. If these mildew spots when young are rubbed smooth, especially on the green stems or berries, we see below them, in the epidermis of the vine, the mycelium or stem of the fungus spreading in all directions from a central point, like the roots of a tree or plant. This part of the mildew corresponds with the stem and root of a plant, while the upper, powdery part is the one which produces the spores or the seed, conidia and peritheca, all of which are reproductive organs. The grapes thus attacked gradually dry up or crack open. The leaves are eaten through and dry up, and the whole plant becomes badly diseased, and may even die.

History and Distribution.

—The powdery mildew or Oidium was observed for the first time in the year 1845 in hothouses in England. It immediately began to spread, and in a few years infested all the vine districts of the Old World. Before any remedy had been discovered, many vine districts were so injured that they have not since been able to recover. Thus in 1850 and 1851 France suffered greatly from this mildew, and the Island of Madeira, which for three hundred years had produced the finest wines, had its grapevines so injured that they up to this time have not again produced as good a quality of grapes as before the advent of the disease. The Grecian Islands as well as Morea were also visited by the powdery mildew, and though the latter is now kept in control, the general opinion is that the quality of the currants is not as high as it was before the mildew appeared. Now there is probably no place in the Old World where grapes are not attacked by this mildew, although some places are injured much more than others. Adjoining vineyards are often differently attacked, some being even entirely free, while others are visited yearly. Young vines are less attacked than old ones, and in favorable places the mildew seldom infests vines before they are two or three years old. Elevated places and localities exposed to winds and cold are generally attacked by the first stages of this oidium, while its second or last stage prefers low, damp places exposed to dew or fog.

The American form of the powdery mildew or Uncinula spiralis differs in some respects from the European Oidium, not as to its effects, but as to its microscopical characteristics. The Oidium occurs in Europe only with certain generative organs called gonidia, while the American Uncinula also develops so-called peritheca. It is more than probable that both fungi belong to the same species, but until these perithecal organs have been found on the European Oidium, the proper name for our mildew must be Uncinula, and not Oidium. It is also probable that the Uncinula fungus is a native of this continent, and that it from here has spread to Europe, where the natural conditions are such that only the gonidial form of the fungus has been able to develop. In general appearance and in their effects the Uncinula and Oidium are identical.

The Oidium appears sooner on poor soil and on exhausted vines, and vines in which the flow of the sap for some reason or other has been checked are more subject to the mildew than those which are yet in full growing vigor. Elevated vines on trellises which are much exposed, and vines which are so covered up that the air has little access, are the first ones to be attacked, and those which will suffer the most. The powdery mildew affects all varieties of grapes, but some kinds more than others. The Muscats are among those which suffer considerably, and if not sulphured would in severe cases neither set nor bear suitable grapes. The Malaga is less affected, and so is the Sultana. In new districts the Uncinula does not appear until the vines are older. Thus in the Fresno district the earliest vines did not suffer from mildew until they became five years old, but now the mildew would destroy the grapes every year, in case they were not treated with sulphur.

Remedies.

—The most common and perhaps the best remedy is powdered sulphur. The latter is applied either with the dust can or “dredger,” or with bellows. The dust can is used when the vines or vine shoots are yet small, and the bellows when the vines are larger. The first sulphuring should be done when the young shoots are six inches long, immediately before the bloom, and the second time when the berries are well set. Sulphuring as a regular vineyard operation will be more fully discussed further on.

DOWNY MILDEW OR PERONOSPORA.

General Notes.

—The downy mildew is a fungus known botanically as Peronospora viticola. Its native country is the United States, but its greatest damage is done in Europe. It appears as white, downy spots on the underside of the grape leaves, which are gradually destroyed, and later on attacks the berries, which shrivel and spoil. In California the downy mildew occurs frequently on wild native grapevines, but only very rarely on the cultivated Asiatic vines. Dr. H. W. Harkness, the eminent mycologist, found it only once on cultivated vines in the Sacramento river bottom. These vines were growing close to native vines, from which the fungus had spread. There is no fear that this fungus will ever spread and cause damage in our State as long as the vineyards are given plenty of air. In France the Peronospora has caused much damage, but is now being combated with bluestone and lime solutions, according to the following formula: Slake thirty pounds of lime in seven and a half gallons of water, also mix sixteen pounds of bluestone (copper sulphate) in twenty-five gallons of water. Mix the two together, and either sprinkle the foliage with it, or dilute it further with say five hundred gallons of water and spray the vine leaves on both the upper and lower sides. According to Dr. Harkness the efficiency of this spray cannot always be relied on. So far no other fungi have appeared in the raisin districts of this State, nor have we reason to fear that any will attack the vines.

THE VINE PLAGUE.

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.

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 IXL 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.

RED SPIDER.

Characteristics.

—Red or yellow mites are quite frequently injurious to grapevines. These mites are small, almost microscopical, and appear in enormous quantities on both sides of the leaves, especially, however, on their under side. They cover the leaves, and even the ground of the vineyard, with a thick cobweb, in which they live and hatch. Dry air and heat promote the wellbeing of the mites, and hasten the injury they do to the vine leaves, which soon dry up and check the growth of the vines. On the contrary, dew and moisture destroy the red mites in a short time, and in places near the coast they are seldom very injurious.

Remedies.

—Sprays of various kinds, such as whale-oil soap, resin sprays, etc., have been used. Frequent spraying with pure water will destroy the mites, but they will multiply again if the climate is favorable. The best success is had with a spray of a compound known as the IXL compound, which is used in the proportion of five pounds of the compound to thirty gallons of water. One good spray will destroy both the mites and their eggs.

CATERPILLARS.

Characteristics.

—The caterpillars which trouble the raisin grapes are confined to three or four kinds. The most common and also the most destructive are the very large larvÆ of the sphinx moth. The common grapevine sphinx (Philampelus achÆmon) is a large larva, incorrectly called a worm, which is, when full grown, over three inches long. The color varies from bluish green to brown, with several lighter stripes on each side. The head is truncate, and the tail is furnished with a curved horn. The pupa hibernates in the soil below the vines, and is about half the size of the full-grown caterpillar. The full-grown moth is about two inches long by two and one-half inches between the outstretched wings. The eggs are laid by the moths on the leaves of the vines. Two broods of caterpillars appear yearly under favorable conditions, or else only one brood, which generally appears in the end of July. The caterpillars grow with great rapidity, and attain their full size in a few weeks. The pupÆ hibernate in the soil and hatch the following summer.

Another large grapevine caterpillar is the Deilephila striata, which is about the same size as the AchÆmon. The moth has more pointed wings, with narrow stripes, and the larva is brighter colored, often yellowish green, with several colored stripes on the sides. The eggs are not laid on the vines, but on the weeds on the vacant lands outside the vineyard, especially on species of Epilobium, but also on other weeds, and they hatch and feed on them. The caterpillars feed in ordinary years only on the weeds on which they are bred, but in other years which are especially favorable to their enormous increase they migrate to the vineyards and feed on the vines at the most alarming rate. The caterpillars of both the above large moths vary in color from green to brown or violet brown, but as a rule the Deilephila is more brightly colored than the AchÆmon. The former is more active and often travels in enormous numbers, when it is called the army-worm. The AchÆmon is more blunt at both extremities, the head being almost truncate.

Vineyard Scene, Rosedale Colony, Kern County, July, 1890.—Three Months After Planting.