UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CIRCULAR 353 November, 1942 PIERCE'S DISEASE OF GRAPEVINES WM. B. HEWITT/ NORMAN W. FRAZIER,-' h. E. JAC0B,=' AND J. H. FREITAG* Pierce's disease of grapevines, now present in most of the vineyard districts of California, is killing large numbers of vines in these areas. The disease is characterized by delayed foliation and dwarfing of the vine; mottling; and, later in the summer, burning and drying of the leaves ; wilting and drying of the fruit ; failure of the canes to mature evenly in the fall ; and ultimately the death of the vine. This very destructive disease was first reported in California vine- yards some fifty-eight years ago. It was known then as the Anaheim disease, or California vine disease, and when observed for the first time in a new locality it was often given such names as vine plague. Emperor disease, and mysterious vine disease. In southern California the disease was observed near Anaheim and Pomona during the year 1884. Its distribution apparently extended throughout the entire Santa Ana Valley, thence northwesterly through Los Angeles and eastward into San Gabriel Valley through Azusa, and south from Anaheim into San Diego County. The disease also occurred north of Los Angeles throughout the San Fernando Valley and even into the Antelope Valley. By 1895 it was responsible for the destruction of 30,000 to 35,000 acres of thrifty productive vineyards. During 1887 and 1889 the same disease was reported in vineyards of Napa Valley and northern Sacramento Valley, but apparently did not become epi- demic in these northern valleys. ^ Assistant Professor of Plant Pathology and Assistant Plant Pathologist in the Experiment Station. -' Graduate Assistant in Entomology. ^ Associate in Viticulture and Associate in the Experiment Station. * Instructor in Entomology and Assistant Entomologist in the Experiment Station. [1] 2 University of California — Experiment Station Early studies of the disease were made by Newton B. Pierce, of the United States Department of Agriculture, who published in 1892 an elaborate account of his studies/' Many quotations might be extracted from Pierce's bulletin which parallel very closely the present symptoms, spread, and development of the malady, and death of vines as it now occurs in this state. E. Dowlen, under the auspices of the Board of State Viticultural Commissioners of California, worked experimentally with the vine disease in southern California. Some of his studies were pub- lished in the annual reports of the Board.*' ^ In addition to the studies reported by these two men, there were others who made observations and some who conducted experimental work on the nature of this disease. Both Pierce and Dowlen came to similar conclusions : that the disease which caused the death of the vines in southern California was due to some very obscure disease-producing agent that in their opinion was not either bacterial or fungus but was, nevertheless, contagious and spread through the vineyards. They fur- ther concluded from their studies that the disease was not associated wdth any soil types or cultural and irrigation practices. Losses in vineyards of southern California began to decline about 1895, and by this time young plantings near the margins of the diseased areas were developing with the loss of only a few vines each season. After 1900 the disease became obscure or passed unnoticed and very little is known of its occurrence until the recent outbreak of Pierce's disease in the San Joaquin Valley, except that vines of vinifera grape varieties have been notoriously very short-lived in many of the southern California districts. No records have been found which indicate that the old Anaheim, or California, vine disease occurred in the San Joaquin Valley during this early epidemic in southern California. In fact. Pierce suggested that the San Joaquin Valley was a good place to obtain disease-free cuttings.** The earliest record found which indicates the presence of the disease in the Valley describes a mysterious death of vines in Tulare County in the spring of 1920." Other unpublished accounts indicate that the disease was present in some vineyards near Exeter in Tulare County in •"•Pierce, Newton B. The California vine disease. U. S. Dept. Agr. Div. Veg. Path. Bui. 2:1-221. 1892. ^ Dowlen, E. Report of Ethelbert Dowlen. Annual report of the Board of State Viticultural Commissioners of California 1889-90:57-63. Sacramento, 1890. ^ Bichowsky, E. C. The vineyards of southern California. Eeport of the Board of State Viticultural Commissioners of California. 47 p. Sacramento, 1893. (See specifi- cally report of E. Dowlen, p. 9-11.) '^ Pierce, Newton B. Grape diseases on the Pacific Coast. U. S. Dept. Agr. Farmers' Bui. 30:1-14. 1895. •*Dieback of Emperor grapes. California Plant Pathologist 1(2): 12-20. March, 1921. ^1^-3^2] Pierce's Disease OF Grapevines 3 1927. Since that time the disease has been found in nearly all of the vineyard districts of the state. The total losses due to Pierce's disease are difficult to estimate, but they have become increasingly greater during the last few years, varying from a few vines in some vineyards to nearly complete destruction of other plantings. The disease has been observed to increase in some vine- yards from 5 per cent diseased vines to over 30 per cent diseased vines during a single season, while in others the spread of disease has been slower. The future course of Pierce's disease is unpredictable, but its destruction of the southern California vineyards prior to 1900 demon- strates its possibilities. TRANSMISSION OF PIERCE'S-DISEASE VIRUS Experimental work with Pierce's disease since 1936 has shown that it is caused by a virus,^" a disease-producing agent, which exists and multiplies in the tissues of the grapevine. This was proved by the fact that the virus has been transferred, in experiments, from diseased vines to healthy vines by grafting a piece of the diseased vine upon a healthy one. Such grafting experiments, using both root and cane pieces from diseased vines, conducted during 1936 and 1937 and many times since, have clearly demonstrated the disease to be transmissible in this way. VIRUS IN NURSERY STOCK AND CUTTINGS Pierce's disease may also be spread in nursery stock. Experimental plantings of cuttings from diseased vines have shown that Pierce's disease is carried in a high percentage of the cuttings. The majority of the cuttings taken from diseased vines died during the first year in the nursery row, though some diseased cuttings lived through the second year and a few remained healthy. Pierce also found this to be true."^^ He states, "Studies of this malady have revealed the fact that cuttings from diseased vines are themselves diseased, and that the degree or amount of disease in the cuttings is proportionate to the degree or stage of disease in the parent vine." Pierce's disease has not been experimentally spread from diseased vines to healthy vines by pruning or cultivation tools. Field observations and greenhouse plantings show that the disease is not carried in the soil, nor spread by irrigation water, facts which are also in agreement with the observations of the earlier workers. ^"Hewitt, Wm. B. A transmissible disease of grapevines. Abstracted in: Phyto- pathology 29:10. 1939. ^^ See citation in footnote 5, page 2. 4 University of California — Experiment Station DISTRIBUTION OF THE DISEASE IN VINEYARDS Field observations sliovs^ that Pierce's disease may develop in vines ol* any part of the vineyard. The first few diseased vines are often found irregularly scattered through the vineyard or along one side. In many vineyards observed, most of the spread has been in irregular localized areas around the original centers of infection, v^hile in others the spread has been more general. The disease has also been observed to develop more rapidly in vigorously growing vines than in weak vines. It has spread very rapidly in and near wet spots, along roadsides, irrigation canals, ditch banks, and borders of vineyards where grasses and weeds have been allowed to grow. Leafhopper vectors have been found most abundantly in these areas and are probably responsible for the adjacent disease spread. Pierce's disease has spread rapidly in vine^^ards near certain alfalfa fields and in some districts where alfalfa is extensively planted. SPREAD BY LEAFHOPPERS There are at least three widely distributed species of leafhoppers that are able to transmit or spread the virus from^ diseased to healthy vines; they are the green sharpshooter, Draeculacephala mimerva Ball;"' the redheaded sharpshooter, Carneocephala fidgida Nott. ;'' and the blue- green sharpshooter, Cicadella circellata (Baker). Recent evidence indicates that additional species of sharpshooters may also be vectors. The results of many tests indicate that the grape leaf- hopper, Erythroneura comes (Say), does not spread the virus. Over 50 other species of insects commonlj^ found in vineyards have been tested and failed to transmit the virus. The green sharpshooter (plate 1, A,B,C,D) is a relatively large leaf- hopper with a sharply pointed head. The females are slightly over y^ inch in length and are a pale color underneath. The males differ from the females in being smaller in size and black underneath. Throughout the greater portion of California where this species occurs, adults are typi- cally bright grass green during the entire year, but in some parts of the San Joaquin and Sacramento valleys most of them are dark green to brown in color during late fall, winter, and early spring, appearing bright green again during late spring, summer, and early fall. The redheaded sharpshooter (plate 1, E, F) is paler green in color and '^ Hewitt, Wm. B., N. W. Frazier, and Byron E. Houston. Transmission of Pierce's disease of grapevines with a leafhopper. Abstracted in: Phytopathology 32:8.1942. ^^ Determinations of the species of leafhoppers were made by Dr. P. W. Oman, Entomologist, United States Bureau of Entomology and Plant Quarantine, Wash- ington, D, C. CiR. 353] Pierce's Disease of Grapevines 5 can be distinguished from the green sharpshooter by its slightly smaller size and by its brownish to reddish head, which is rounder in shape. The males are smaller than the females and have smoky wing tips. The blue-green sharpshooter (plate 1, G, H) is intermediate in size between the green and the redheaded sharpshooter and is less robust than either. In northern California it is green or bluish green with an ivory to yellowish rounded head, which bears several characteristic black marks. It is yellow underneath and has yellow legs. In southern Cali- fornia it is often bright blue. The green sharpshooter occurs in all the principal grape-growing areas of California ; it has been found more widely distributed over the state than the redheaded sharpshooter. It is commonly found in moist situa- tions, as in marshes and bogs, along streams and ditches, and in wet areas created by irrigation practices. Well-irrigated alfalfa fields which have a thinning stand of plants contain certain grasses that provide favorable situations for large numbers of this leafhopper. Populations of this leafhopper have also been observed in young grain fields, in orchard covercrops, in uncultivated areas around buildings, on lawns, along roadsides, railroad rights-of-way, irrigation ditches, and canals, and in permanent pastures. The redheaded sharpshooter has in general been found under the same conditions but favoring open or exposed soils which support low, sparsely growing grasses and weeds. Grasses afford preferred food and breeding plants for both the green and the redheaded leafhopper, Bermuda grass being especially favored. They are also commonly found on puncture vine and cocklebur. The blue-green sharpshooter occurs throughout most of the grape- growing areas of California. It is very common and often abundant especially in canyons and along streams in valleys in the coastal fog belt. In the San Joaquin Valley it is sometimes found in large numbers but usually fairly closely confined to stream banks and rarely on cultivated grapes in near-by vineyards. This sharpshooter is found on many hosts, but prefers vines, shrubs, trees, and perennial herbs ; grasses and weeds are less commonly infested. Wild grape, wild blackberry, elderberry, and willow are especially common hosts. In coastal areas the blue-green sharpshooter is often very abundant in vineyards, where it may be present on the vines from the time of early spring growth until growth has ceased in the fall, during which time continual reproduction may take place with several hundred nymphs and adults occurring on one vigorous vine. This leafhopper appears to be more important in the spread of Piercers disease in the north coastal vineyards than either of the other two leafhopper vectors. 6 University of California — Experiment Station TYPICAL SYMPTOMS OF PIERCE'S DISEASE The symptoms of Pierce's disease" are found to vary with the grape variety, and to some extent with the same variety grown in different localities under different climatic conditions. The variation due to local- ity is generally in the degree and rapidity with which the symptoms show and not necessarily a difference in the type of symptoms in the leaves, canes, fruit, and general growth habits of diseased vines. There are several characteristics of the disease which are common to many varieties such as delayed growth, leaf mottling, dwarfing, leaf burning and scald- ing, wilting of fruit, and uneven maturity of canes ; these are described in the paragraphs to follow, and compared with the symptoms of little- leaf and black measles in table 1. Belayed Growth. — In the spring diseased vines or parts of diseased vines usually start growth from a few days to as much as 2 weeks later than healthy vines (fig. 5, 5) . Other troubles such as bud mites, freezing injury, arsenic spray injury, lack of complete dormancy, and overcrop- ping will also cause entire vines or parts of vines to start growth late; these, however, generally appear 'in rather large numbers of vines or in definite areas, and the vines usually recover. On the other hand, vines with Pierce's disease do not recover. In early stages of disease spread in the vineyard, the affected vines are usually irregularly scattered among normal vines. In advanced stages of disease spread throughout a vine- yard, diseased vines often are grouped in irregular areas. Vines that start growth late are suspects and may be marked and observed later for other symptoms. Leaf Mottling. — In most varieties the first few leaves developing on young shoots of diseased vines are characteristically mottled (figs. 1, 2, 3). However, some varieties apparently seldom or never show this symptom, and others do so only occasionally. References to the variations in specific varieties are made later in this paper. The mottled leaves that develop with the new spring growth are usually most abundant on shoots or canes which start growth late, but may develop on shoots which appear otherwise vigorous and normal. The mottling is characterized by the formation of a lighter-green color (chlorosis) in the leaf tissue between the small veins (fig. 1). In the early stages these light-green areas or spots are usually well defined and limited by the small veins (plates 2 and 3) . Often this mottling appears more as an interveinal chlorosis or as though the veins were bordered by dark-green tissue (vein banding, as in figure 4 and plate 4) . The tissue ^* Hewitt, Wm. B. Pierce's disease of grapevines. The Blue Anchor 18(3) : 16-21, 36. August, 1941. CiR. 353] Pierce's Disease of Grapevines between the veins often appears stretched, or tightly drawn, and smooth and shiny on the upper surface (fig. 1, 5). As the leaves become older, the mottled areas in some may enlarge to include the small veins until Fig. 1. — Leaves of grape showing symptoms of Pierce's disease: A, leaf of the Emperor variety v^^ith mottling characterized by a dispersed interveinal chlorosis; B, Emperor leaf illustrating severe form of mottling in which the light-colored tissue appears tightly stretched ; C, leaf of Muscat variety show- ing typical interveinal chlorosis mottling (compare with Muscat leaf spot, fig. 6) ; D, Emperor leaf in late stages of disease. This leaf had previously shown the vein-banding type of mottling ; the green color has faded to yellow, except around the large veins, and the margins are drying up. green tissue remains only around the larger veins (fig. 1, D). The mot- tling is usually distributed over most of the leaf surface, though in some leaves it may be found irregularly scattered or only in localized areas (figs. 1, A, and 2). The mottling is usually visible on both surfaces of the leaf, but is more easily seen on the upper. 8 University of California — Experiment Station Mottling generally shows in the first few leaves formed on the cane. It is usually more intense in the first leaves and becomes less intense with each new leaf formed as the cane grows (fig. 2). Thus, shoots have Fig. 2. — A shoot from a Malaga vine with Pierce's disease. The leaves at the base of the shoot are severely mottled while the tip leaf does not show this condition. The mottling in some leaves has devel- oped into typical vein banding. The leaf at the upper left next to the tip shows faint dispersed mottling on the left side, distortion and vein banding on the right side. mottled leaves at their base and apparently normal leaves farther out toward the tips. This condition may create the impression that the vine is recovering, but it is a normal symptom of Pierce's disease and the vines will show more intense symptoms later in the season. CiR. 353] Pierce's Disease of Grapevines In many varieties the mottled leaves are v^rinkled or puckered along the large veins, and irregular, cupped, one-sided, or othervv^ise misshapen (figs.l,B,and2). Fig. 3. — Symptoms of Pierce's disease : A, shoot of the Palomino variety showing leaf burning and scalding and basal defoliation with leaf stems (petioles) remaining attached to the shoot; B, early stage of leaf scorching advancing inward from the margins of the leaf; C, leaf of Tokay variety showing slight dispersed mottling and yellow leaf spots which turn red with age. The degree of leaf mottling, wrinkling, and deformity varies with individual leaves, vines, varieties, and the stage to which the disease has progressed in the vine. As the season advances, the chlorotic areas in many leaves, particularly those on vines having advanced stages of disease, become yellow in the varieties with white or light-colored fruit 10 University of California — Experiment Station and pink to dark red in the varieties with red-colored fruit (plate 4). In varieties with red or black fruit a yellow color often precedes the formation of red color in the leaves. Dwarfing of Vines. — Entire vines or parts of diseased vines, particu- larly those which start growth late, are usually dwarfed. The degree of dwarfing varies with the stage of disease in the vine ; the dwarfing shows - m^ ^ ^^^m r g % b ^ ^ISR k' Fig. 4. — A shoot from a Malaga vine in an advanced stage of Pierce's disease. The basal leaves show clearing between the large veins which often follows more typical leaf mottling and also mar- ginal burn. The tip leaves show typical vein banding. as shorter growth in shoot length and internode, and also smaller leaves (fig. 5). The size of leaves is often proportionate to the length of shoot growth. Dwarfing usually shows first in the second season of disease and becomes more pronounced each season until the vine dies. In early stages of disease, the dwarfing may show in the shoots of but one spur or arm which may soon be covered up by other shoots. This dwarfed grov/th is usually very striking in contrast to the growth of healthy shoots and also to the previous season's cane growth ; the latter is indicated by the diameter of the spur or fruiting canes, which is usually large in contrast to the small size of the dwarfed shoot. CiR. 353] Pierce's Disease of Grapevines 11 Leaf Burning and Scalding. — From mid-June on into fall, leaves of disease^ vines may dry or burn. Mottled leaves usually burn first about the margins and then between the large veins, though in some varieties mottled areas in the leaf blade dry up (fig. 4 and plate 4). The burned r Fig. 5. — A, Ribier vine in the second season with Pierce's disease; the vine produced only short growth on a few spurs and was dead by midsummer; B, Thompson Seedless vine with Pierce's disease ; the shoots from the fruiting canes are badly dwarfed. The leaves showed characteristic mottling which is not very clear in the photograph. The renewal spurs have produced fairly long shoots up the center of the vine. tissues often turn yellov^, then dry and turn brown to red, according to the variety. Nonmottled leaves of diseased vines may also burn, in these the burned areas usually start at one or two points in the leaf margin and increase in size toward the center of the leaf (fig. 3, A and B), and are often bordered by a band of yellow tissue. 12 University of California — Experiment Station Leaf scalding is characterized by a sudden drying of the leaf tissue while still green and is often the first symptom of disease in a .vine. A portion of the leaf, usually about the margins, will dry up while still green, and later these areas of dried tissue enlarge progressively leaving definite lines of dark tissue bordering each successive zone of dried leaf tissue (fig. 3, B, and plate 2). Leaf burning and scalding may develop on a single shoot, or in many leaves scattered over the diseased vine. The degree to which leaf burning and scalding develop will vary a great deal with the individual vine, locality, and season. Burning is usually more pronounced and develops earlier in the interior valleys than in the coastal areas. When leaf burning becomes severe, the leaves often drop from the canes, usually leaving the leaf stem (petiole) attached to the cane. These leaf petioles dry up and fall later. Other vine troubles, particularly alkali injury and severe cases of black measles (Spanish measles), will cause leaves to burn and drop in a similar manner, so care should be exercised in using this type of leaf fall as a symptom solely characteristic of Pierce's disease. Vines which drop their leaves because of black measles often leaf out again, while those which drop their leaves because of Pierce's disease very seldom leaf out the same season unless severely pruned. The symptoms of black measles are discussed later. Wilting and Drying of Fruits. — The effect of the disease upon the fruit varies a great deal with the variety and locality. Diseased vines of many varieties often fail to set any fruit after the first season of disease while others set fair crops. The blossoms fall from the clusters during bloom or just after bloom, then the entire cluster stem will drop. Much of the fruit which does set develops but is usually small in comparison to the fruit on healthy vines. At any time after early July until fall, the fruit may soften and dry up on the vine. Fruit of colored varieties will develop color prematurely, then soften and dry up. The fruit may be found in varying stages of wilting and withering (waterberry) to com- pletely dry on diseased vines after midsummer. Other factors such as black measles, overcropping, and sunburn may also produce wilting and drying of the fruit. Symptoms on Shoots and Canes. — The shoots developing on diseased vines grow to varying lengths, according to the variety, their general vigor, and the stage of disease in the vine. From midsummer until fall some shoots will die back from the tips, along with severe leaf burning. Many of the shoots develop a yellow sunburned appearance of the bark. In the fall as the wood matures, the bark on the canes of healthy vines matures to a tan or brown color. On diseased vines many of the canes CiR. 353] Pierce's Disease of Grapevines 13 will mature unevenly ; there will be irregular green patches in the bark along the portions of the canes which should be fully mature (plate 2). After the first frosts in the fall, these green areas in the canes turn black, dry out, and become sunken and cracked. When pruned these canes are usually brittle and snap off instead of being firm and solid. The canes and other woody parts of diseased vines are, in general, dryer than those of healthy vines and do not bleed so freely or fail to bleed at all from pruning wounds made in the spring. Effect on Roots. — The death of the root system of diseased vines usually follows the death of the top. The roots in the first season of disease are usually in good condition while in the second season many of the roots die back. Some diseased vines produce groups of small roots near the crown, and occasionally suckers arise from about the same place. New Cases of Disease. — The first symptoms which show in new cases of Pierce's disease may begin to develop at any time from mid- June until fall, and the degree to which they develop that season depends to some extent upon the time the first symptoms begin to show. The affected shoots stop terminal growth while those on healthy vines about them continue growth. A few leaves on one or more shoots develop scalding as previously described under leaf burning and scalding. After the scorching of these first few leaves, other leaves over the vine may develop scald in a similar manner. Many of the leaves turn slightly yellow, giving the vine a yellow cast or pale-green color. Often the basal leaves of the canes continue to turn yellow while others develop varying degrees of yellowing, scalding, burning, and drying up. The leaves of some vines have been observed to just wilt and dry while still green. This has been particularly true with the variety Ribier. Effect on Young Vines. — Young vigorously growing diseased vines of many varieties wilt rather suddenly. On these vines many leaves or parts of leaves dry up while still green as if scalded. These symptoms may show in only a portion or over most of the young vine. They may either develop suddenly or progressively over considerable time. If these af- fected portions of young vines are pruned off to short spurs, the vine will often start new growth. The leaves of the new growth show mottling typical of the disease. Such vines may die during the summer, but those affected late in the season often live through the winter and are usually dwarfed and produce mottled leaves the following spring. Effect on Old Vines. — All varieties studied of the vinifera, or Euro- pean, varieties of grapes affected with Pierce's disease die. Vines of some varieties die during the first season that the disease is apparent, while vines of other varieties may live from one year to four or more. Many 14 University of California — Experiment Station American varieties will live much longer with the disease. Pierce de- scribed the progress of the disease in several of the southern California vineyards during the epidemic of this vine disease between 1884 and 1900.'' He observed considerable variation in the time required for the death of vines and complete destruction of the vineyards, stating, "In some cases certain vines live for five years, or even more ; in other cases they appear to die in one season. In some cases entire vineyards will seemingly succumb in a single season. . . . the death of a vineyard once badly diseased is only a question of time. The time generally re- quired to kill the majority of vines in a vineyard is from two to five years, according to variety, age, " Vines of some varieties may appear almost normal in the fall but fail to leaf out in the spring, though the wood still seems to be alive. When the tops of diseased vines fail to leaf out, they may sucker from the base. These suckers may develop into vigorous canes. Generally the leaves of these suckers show mottling, though sometimes they do not. The death of most diseased vines usually occurs between midsummer and fall after they have shown varying amounts of shoot growth, leaf mottling and burning, wilting and drying up of fruit, and dying-back of canes. The season when death occurs depends upon the variety, age of the vine, and locality. VARIETIES SHOWING TYPICAL SYMPTOMS The varieties listed below produce, in general, the foregoing typical symptoms of Pierce's disease ; that is, dwarfing and mottling in the basal leaves of the shoots, leaf burning and scalding, and immature patches in the bark of the canes. The symptom variations of these varieties are not considered sufficient to discuss in detail. The length of time these varie- ties may live after becoming diseased varies from two to four or more years. Herbert Hunisa Inzolia bianea Khalili Malaga (White Malaga) Molinera (Eed Malaga) Mondeuse Moreto Muscadelle Muscat Hamburg Niagara Noah Almeria (Ohanez) Angulata Beclan Burger Cabernet Sauvignon Carignane Danugue Delaware Emperor Golden Muscat Green Hungarian Gros Colman Olivette Blanche Palomino (Napa Golden Chasselas) Pearl of Csaba Rambola Saint Emilion (Trebbiano) Sauvignon vert Semillon Sylvaner Thompson Seedless (Sultanina) Zinfandel 1^ See citation in footnote 5, page 2. CiR. 353] Pierce's Disease OF Grapevines 15 VARIETIES SHOWING DIFFERENT SYMPTOMS Some varieties have been found to vary considerably from the typical symptoms listed above. The follow^ing paragraphs discuss the symptom variations of some of these varieties. Bihier (Alphonse LavalUe) and Fehrer Szagos. — Mottled leaves have very seldom been observed on diseased vines of these varieties, though some mottled leaves have been found on suckers arising from the trunks and bases of diseased vines which have been sawed off. Often the diseased vine dies suddenly during the summer; it first stops growing and gen- erally appears to be darker green than adjacent vines ; then the leaves and fruit wilt and the vine dries up, much as if it had been cut off at the base. Other vines which appear healthy and to be growing vigorously may wilt and dry up within a few days. Some diseased vines stop gro^\- ing and gradually dry up in a period of 2 to 4 weeks. The fruit on a portion or on most of the vine is often smaller than that on healthy vines, and as the vine declines the fruit usually withers and dries up. Vines which become diseased late in the season often live over the winter and leaf out late the following spring ; they produce weak feeble growth and then die by summer. Alicante Bouschet, Mataro, Petite Sir ah, and Troiissean. — Although varying somewhat, these varieties exhibit the following symptoms : delay in leafing out in the spring, very marked dwarfing of the canes after a year of vigorous growth, immaturity of the canes, leaf burning, and suckering from the crown. Occasionally these varieties have been ob- served to produce mottled leaves at the base of the canes during the second season of disease. When leaf mottling does occur, it is like that previously described. Burning and drying of the leaves are the most prominent symptoms of vines in early stages of disease. The fruit will often be small and during the summer may wilt and dry up on the vine, though this will vary a great deal on individual vines and varieties. Flame Tokay (Tokay). — Leaves at the base of the shoots of Tokay develop characteristic mottling like that described above. However, at any time during the season the leaves farther out on the canes may develop dark-red spots (fig. 3 (7), usually irrespective of leaf mottling. These leaf spots resemble those produced by black measles, and in the absence of mottled leaves at the base of the shoot it is difficult to differen- tiate Pierce's disease from black measles. Vines with black measles, how- ever, often have spotted fruit. Mission. — Vines of this variety usually show leaf scorching and burn- ing during the season they become diseased, and the grapes wilt and 16 University of California — Experiment Station dry up. Even large vigorous vines have been observed to wilt suddenly and dry up. Mission vines which live into the second or third season are dwarfed and the leaves characteristically mottled. The chlorotic areas between the leaf veins and also the margins of the leaves usually turn very red during the summer. Thompson Seedless (Sultanina) and Sultana. — These varieties are very much alike in their reactions to Pierce's disease. Leaf mottling, scorching, burning, shoot dwarfing, and fruit withering in these varieties Fig. 6.— Muscat leaves showing the Muscat leaf spot typical on the leaves of normal vines of this variety from midseason on into fall. These spots originate at the small veins and gradually increase in size in a manner similar to the leaf spot of black measles. are like the typical symptoms previously described. The diseased vines usually start growth late, the shoots arising from the fruiting canes are dwarfed, and the leaves at the base of the shoots may or may not be mottled. However, mottled leaves are nearly always formed on some of these shoots. In the early stages of disease the shoots from renewal spurs and suckers often grow rapidly and cover the dwarfed shoots on fruit- ing canes, so it is easier to find the leaf mottling before these shoots have grown very long. The fruit developing on dwarfed shoots is usually small and frequently withers and dries up before harvest. The old vines often live three or four years after they become diseased but seldom produce marketable fruit after the first year. Each year these vines become progressively weaker until they die. Little-leaf (discussed later in the circular under its own heading, and in table 7) is often confused with Pierce's disease in these varieties. -m r Plate 1. — Leaf hopper vectors of Pierce's disease of grapevines: A, male, and B, female, green sharpshooter, Draeculacephala minerva; C, male, and D, female, brown form of the green sharpshooter occurring in certain locali- ties; E, male, and F, female, redheaded sharpshooter, Carneocephala fulgida ; G, male, and H, female, blue-green sharpshooter, Cicadella circellata. (All X 10.9.) (After Henry H. P. Severin.) Plate 2. — Pierce's disease of grapevines: A, Leaf of Emperor variety with typical mottling (chlorotic between the veins). B, Leaves showing scalding, which is usually marginal and may involve large areas ; the upper leaf shows a band of dark tissue bordering the scalded area. C, Canes showing immature green patches in the bark ; the cane on the left is from a healthy vine, the other three canes from a diseased vine. bO en o . JB " 3 rt c S '> O) bJO o 2 .S -(^ t: CD "w C fig" o) > 52 02 «^ S ^ 5^ o 00 o c # 11 1 1 L. ^■,:^, ^ %,. :« ^^^MB ma *^^ ^ K^' ' .^hi^ m^^ \:-'m Fig. 8. — A three-year-old layer from an adjacent vine replacing a missing vine in a cordon-pruned Emperor vineyard. A wire has been placed around the layered cane at "W" to hasten the development of the new vine, which is ready to be cut from the parent vine. (From Ext. Cir. 101.) vineyards that are cross-cultivated. The methods are best suited to trellised vineyards but may be used also in head-pruned vineyards that are cultivated in one direction only. Layering. — At pruning time, a long well-developed cane from an adjacent vine in the row is selected and left uncut to a length sufficient to bend down to a foot or more below the soil level at the position where the new vine is desired, and up again with one or more buds above the surface of the soil. If the cane is sufficiently long it may be used to form the trunk of the new vine ; this eliminates most of the labor of training the new vine the following summer. Figure 7, A, illustrates such a cane in a cordon-pruned vineyard. In the spring before growth starts (February or March) a hole, 12 inches or more deep, is dug at the side of the stake where the new vine is to be, and the layer cane is bent down into the hole with the end of the cane projecting aboveground at the stake. A wire 22 University op California — Experiment Station is wrapped around the cane, preferably at its lowest point, and the ends twisted together to make it snug. The hole is then filled with top soil firmly packed around the cane (fig. 1,B). Wire of 18 g*auge is a good size to place around the layer cane. If the wire has been omitted when the layer is made it may be put on later anywhere between the mother vine and the soil. As the cane grows and enlarges in diameter the wire will WB W^ 1 1 A 4 ■ m ^ i ■ 1 ^ ^ w 1 "^ Pig. 9. — Approach-grafting to a newly planted phylloxera- or nematode- resistant rootstock rooting to replace a missing vine in a grafted vineyard. A illustrates the cuts made as described in the text ; B, shows the completed graft ready to be covered with a mound of soil. At a is a cane from an adjacent vine into which the top of the rootstock rooting & is grafted. become tight and act as a girdle, allowing water and soil nutrients to pass from the mother vine into the new vine but checking the movement of elaborated food materials from the leaves of the new vine to the mother vine; this causes the new vine to grow more rapidly than it would without the wire girdle. Placing the wire at the lowest point of the bend of the layer will cause the strongest roots to develop just beyond that point. Figure 7, C, shows the growth from a layered Emperor vine in June of the second year and figure 8 shows the trunk of a layered vine at the end of the third growing season. Leaving the new vine attached to the mother vine for three seasons will establish the new vine most quickly. It may be removed at the end of the second year if the danger of inf ec- Cm. 353] Pierce's Disease of Grapevines 23 tion from Pierce's disease is great. If the mother vine becomes diseased before the layer is cut off the new vine v^ill usually become diseased ; likevrise if the new vine becomes infected before removal from the mother vine, the latter will usually contract the disease. Cutting the layer at the end of the first season is not advisable unless the danger of infection is very great. '% j5 ^^ f '^^ 1 ''H ^ -^g^^i pp ^m-^ Jm 1^ ^^^pjIp w~ ^ V '' ^^^^F. ' ^11 1 #♦. ' mr 1H|V^^^ i^^ _„ m^-. Mm.^ HhB^^m|||ljT^v^^ ^i^^^^l^^^^^HI '^^ 1 .-i" €r'3»i ,' i fc^S tet'l^ftftvj: ->, " -' |.::,..*'^^^KM? mm $M0&- ■'■ rig. 10. — A Pinot St. George vine in June of the second season after ap- proach-grafting onto a newly planted St. George rooting. The grafting was done by the method illustrated in figure 9, and corresponding canes are shown in a and h. Approach-Grafting. — A disbudded'^ rooting of the desired rootstock variety is planted in the proper location for the new vine. The top of the rooting is cut off just above the surface of the soil and the rooting is grafted into a cane which remains attached to an adjacent vine. The simplest type of graft for this purpose is made by cutting the top of the stock rooting to a long wedge which is inserted into a long, sloping cut made on the lower side of the cane, taking care to secure a good fit between the cambium layers of the rooting and cane (fig. 9). For best " A disbudded rooting is one from which all eyes or buds have been removed from the stem of the vine by cutting them out with a knife or pruning shears. A properly disbudded vine will produce no suckers. 24 University of California — Experiment Station results the top of the rooting should be of the same diameter as the cane. The union is tightly tied with raffia, twine, or budding rubber and cov- ered with a mound of soil to prevent drying out. A wire is placed around the cane between the mother vine and the graft as described for layering, preferably near the graft. In early summer, after the graft has grown together firmly, the union is uncovered and all roots that have formed on the cane are removed. Thereafter the union is left exposed or covered very lightly with dry soil to prevent sunburn. If the material used for tying the union does not disintegrate and slough off it may have to be cut and removed to prevent girdling. Figure 9 illustrates how the graft is made and figure 10 shows a Pinot St. George vine in June of the second season after approach-grafting. The new vine may be cut off from the mother vine at the end of the second or the third growing season. Eeplacement hy Roofings or Bench Grafts. — In vineyards that must be cross-cultivated, or if more than two consecutive vines in a row are missing, layers or approach-grafts cannot be conveniently used to re- place all of the missing vines. Rootings or bench grafts must then be used. Where this is the case a large hole, at least 2 feet deep and 2 feet in diameter, should be dug. In the bottom of the hole is placed top soil or top soil mixed with well-rotted manure or fertilizer to a depth of about 6 inches. A layer of soil not containing fertilizer should be placed over that which has been mixed with the fertilizer before the vine is planted ; then the vine is planted with moist top soil very firmly packed around the roots. Extra irrigation during the first summer by tanking, or by the use of basins around the new vines, will aid them in getting started. LITTLE-LEAF There are two diseases which may be confused with Pierce's disease of grapevines, namely, little-leaf and black measles.""" These two diseases have been known in the vineyards of the state for many years and no doubt the majority of growers are familiar with them. Their symptoms are compared with those of Pierce's disease in table 1. Furthermore, the control practices of these two diseases have been worked out and are, incidentally, outlined in paragraphs to follow. Little-leaf has been observed in the vineyards grown on certain soils in California since vines were first planted. It occurs in greatest abun- dance in vineyards on sandy soils, to some extent on other soil types, and in places where old stock or barnyard corrals have been. ^^ Hewitt, Wm. B. Black measles and little leaf may be confused with Pierce's disease of grapevines. The Blue Anchor 18(3) :26-28, 40. August, 1941. TABLE 1 Seasonal Comparison of the Symptoms of Pierce's Disease, Littlb-Leaf, and Black Measles of Grapevines Pierce's disease Little-leaf Black measles Spring symptoms Delayed growth from failure of Vines leaf out normally Vines leaf out normally buds to start on eanes and spurs Interveinal mottling in leaves of Slight interveinal chlorosis of In an occasional vine after 3 to many varieties, small dwarfed leaves 4 weeks' growth the small leaves on others (fig. 1; plates veins in the leaves may clear, 2 and 3) the leaf surface have bronze cast, and the leaves drop from Shelling of flowers and drying up of canes some blossom clusters Early-summer symptoms Dwarfed growth on part of vine or Usually good growth except in Normal growth over entire vine, contrasted with severe cases fair to excellent cane growth the previous season, as indicated by previous season's canes and spur diameter First 2 to 12 leaves on canes mottled Chlorotic leaves developing at Leaf veinlet clearing, bronzing, tips of canes; leaves usually and dropping from canes, and small, lopsided, asymmetric, some burning of margins and open at base (fig. 11) and/or between large veins (fig. 13) Fair crop to no fruit; berries often Loose, often straggly clusters Slight speckling of fruit (fig. 12) small on some varieties with small seedless berries Portions of, or entire vines may be affected Summer symptoms Dwarfed growth, with small leaves (fig. 5) Mottled leaves only at base of canes, or over most of canes in severe of disease (fig. 2) Marginal burn of mottled leaves (figs. 1 and 4; plate 4) Leaf yellowing and burning in patches and dropping from the canes (fig. 3 and plate 4) Growth of vine fair to poor, with shortened internodes Chlorotic and misshapen leaves, the condition becoming more intense toward tips of canes Secondary shoots developing, causing vines to appear bushy Growth may stop in canes in one arm or over much of vine Leaf veirdet clearing, spotting, and burning of margins and/ or between large veins (fig. 13) Leaves dropping and dying back from tips Defoliated shoots and canes usually start growth again 26 University of California — Experiment Station TABLE 1— (Continued) Pierce's disease Little-leaf Black measles Summer symptoms^icontinued) Premature coloring, softening, with- ering, and drying up of fruit (plate 4) Canes stop growing and some may die back from tips Vines in late stages dry up and die In some varieties large vigorous vines with good crop stop growth, wilt, leaves burn and vines dry up and die any time from July until fall Leaf scalding — apparently normal leaves suddenly scald and dry while still green; the scald is usually marginal, often involves large areas, and generally devel- ops dark boundary lines (plate 2) Loose clusters with shot berries Fruit mottling, spotting, crack- ing, and drying up on vine (fig. 12) Fall symptoms Dead and dying vines (Same as summer) (Same as summer) Yellowing, burning, scorching, and drying up of leaves Wilting and drying up of fruit Immature green patches in bark of Canes mature evenly Canes mature evenly canes (plate 2) During* 1931 Dr. W. H. Chandler'' demonstrated that little-leaf in certain fruit trees and in grapevines could be cured by adding zinc to the diseased plants. Further work by Dr. Chandler and his associates has shown that little-leaf occurs in many horticultural plants and that the disease is caused by a deficiency of zinc. Symptoms of Little-Leaf. — Vines affected with this disease have little leaves. The size of the leaves varies with the severity of the disease. The effect is particularly marked toward the tips of the canes and in secon- dary (lateral) shoots. ^^ Chandler, W, H., D. K. Hoagland, and P. L. Hibbard. Little-leaf or rosette in fruit trees. Amer. Soe. Hort. Sci. Proc. 28:556-60. 1932. Cm. 353] Pierce's Disease of Grapevines 27 The leaves also develop varying degrees of interveinal chlorosis. The tissue between the veins of the leaves develops less green color than does the tissue about the veins (fig. 11 ) . This form of chlorosis is similar to the Fig. 11. — Little-leaf symptoms in grape leaves: A healthy leaf of normal shape is shown at A. Note the divergent veins and deep petiole sinus with the basal lobes extending down close to the leaf petiole. The other leaves B, C, D, E, and F show varying degrees of little-leaf chlorosis and deformity. The veins are less divergent and the petiole sinus tends to be absent with the basal leaf lobes spread out at the attachment of the leaf petiole characteristic of little- leaf. The leaves B, C, and F show asymmetry and marked attenuation at the base. mottling of the leaves of vines affected with Pierce's disease though often less distinct and more prominent about the margins of the leaves. The chlorosis may be faint to very pronounced. In severe cases the leaves are usually badly distorted and asymmetrically formed. The deformity shows primarily at the base of the leaf where the stem or petiole attaches 28 University of California — Experiment Station to the leaf. Here the veins fail to spread out and the leaf lacks the deep petiole sinus and clasping basal lobes of a normal leaf. This condition shows clearly in figure 11 ; the leaf in the upper left-hand corner is normal and the others show varying degrees of chlorosis and mal- formation. In severely affected leaves the veins become markedly attenuated, suggesting a partly opened fan, while with Pierce's disease the veins of mottled leaves are usually spread out in a normal manner. On vines affected with little-leaf, the first leaves formed on the grow- ing shoot are usually normal or only slightly chlorotic. The chlorosis and deformity become more pronounced with each leaf formed as the shoot grows ; thus, the leaves at the base of the canes are nearly normal and those toward the tips are increasingly more chlorotic. This is in direct contrast to the leaf mottling found on vines affected with Pierce's disease where the severely mottled leaves occur at the base of the cane, and the leaves toward the tip of the cane may be free of mottling. The canes of little-leaf vines often produce numerous lateral shoots with short internodes and small leaves, which give the vine a bushy appearance. On vines which are only slightly affected by little-leaf, the crop is often diminished, the clusters being straggly with many abortive or shot- berries — which are seedless, round, and small. Vines badly affected have a tendency to fail to set fruit and much of that which does set is abnormal . Control of Little-Leaf. — Little-leaf in grapevines may be controlled by supplying zinc to the vines. This may be done in several ways : (1) by swabbing the pruning wounds with a solution of 2 pounds of zinc sulfate to a gallon of water ; (2) by applying zinc salts to the soil; (3) by driving metallic zinc points or nails into the vine trunks; or (4) by spraying the vines with zinc salts. The manner ol treatment depends upon the soil and the variety. More specific details may be obtained from the local farm advisor's office. BLACK MEASLES This disease of the grape is known by various other names in different localities, such as Spanish measles, black mildew, and apoplexy. A simi- lar trouble occurring primarily in old vines has been described in France, where it is called esca ; diseases with like symptoms have also been de- scribed on grapes in many other countries. Symptoms of Black Measles. — The names, black measles and Spanish measles, apply primarily to the peculiar speckling and mottling on the skin of the berries, which are most noticeable in the white and light- colored varieties (fig. 12). This spotted condition of the fruit varies a CiR. 353] Pierce's Disease of Grapevines 29 great deal from vine to vine and from cluster to cluster. Also, the spots ma}^ vary in number from only a few in very mild cases to numerous spots in bad cases. On severely affected vines the fruit often cracks, splits open, and some of the fruit dries up on the vine. The shriveling and dry- ing up of the berries is usually accompanied by bronzing and dropping of leaves and dying back of the cane tips. Fig. 12. — Fruit symptoms of blarck measles: A, Emperor grapes showing spots and color changes caused by black measles. The dark areas are normal color, the light areas abnormal. B, Thompson Seedless fruits having numerous small black measles spots. The leaves of vines affected with black measles develop various degrees of veinlet clearing, bronzing, spotting, and death of tissue between the leaf veins. The leaf veinlet clearing is characterized by a yellowing of the small veins and tissue close to them (fig. 13, A). Many of these areas enlarge into yellow spots which later dry up and turn brown or red (fig. 13, B). The leaves of some vines turn slightly yellow and dry up between the large veins (fig. 13, D) . Vines eight or ten years of age or older are more often affected by this disease than are young vines, but it has been observed in vines only three years old. Vines may develop symptoms of the disease any time during the growing season from early spring until fall. Most cases, how- ever, develop during July and August. Any portion of the vine or the entire vine may be affected and it is common to find only one arm dis- 30 University op California — Experiment Station eased. In some vines the disease appears suddenly. Such vines may entirely lose their leaves within a few days and develop new growth within a short time after they drop their leaves, but some very severely affected vines may die. Measles often shows in vines one season and not the next; badly affected vines show symptoms every season. Fig. 13. — Black measles symptoms in grape leaves : a leaf showing veinlet clearing with the chlorosis diffusing out into the tissues between the veins is shown at A; at J5 is a leaf with necrotic or dead spots and necrotic veins ; C shows yellow spots of varying sizes not interveinal; D, marginal and inter- veinal burning. Control of Black Measles. — The treatment for black measles is to spray or swab the trunk and arms during the dormant season with a solution of 2 pounds of sodium arsenite to 50 gallons of water. Special care should be taken to thoroughly wet all old wounds and cuts. The treatment is applied only after the vines have become entirely dormant. Experience has shown that in seasons when the vines do not become CiR. 353] Pierce's Disease of Grapevines 31 fully dormant it is best to delay treatment to another year. The spray may be applied before pruning or after pruning. If the treatment is made after pruning, it should not be applied to the vines until at least 3 weeks after the vines are pruned, and it must be completed before the buds swell in the spring. If a spray machine is used, a pressure not to exceed 100 pounds is recommended. Sodium arsenite is very poisonous and extreme care must be taken to keep it away from people and animals, and to avoid getting it on the skin or in the mouth and nose of the person applying the spray. Since the material is so extremely poisonous and may injure the vines if applied improperly, it is recommended that those contemplating its use first consult their local farm advisor or someone else thoroughly familiar with its use, and that they work under his direction. SUMMARY Pierce's disease of grapevines, which occurred in southern California in the 1880's and was described under other names, has recently been found in nearly all of the grape sections of the state, and has become epidemic in the central San Joaquin Valley. The disease is caused by a virus transmissible by grafting from dis- eased to healthy vines. The virus is carried in nursery stock and cuttings. It is transmitted in the field by at least three species of leafhoppers, Draeculacephala minerva Ball, Carneocephala fulgida Nott., and Cica- della circellata (Baker). The typical symptoms of Pierce's disease are: (1) delayed foliation; (2) leaf mottling ; (3) leaf burning and scalding; (4) dwarfing of vine ; (5) wilting and drying up of fruit; (6) failure of canes to mature evenly ; and (7) finally death of the vine. Varieties which show typical symptoms include Almeria (Ohanez), Angulata, Beclan, Burger, Cabernet Sauvignon, Carignane, Danugue, Delaware, Emperor, Golden Muscat, Gros Colman, Green Hungarian, Herbert, Hunisa, Inzolia bianca, Khalili, Malaga (White Malaga), Moli- nera (Red Malaga), Moreto, Mondeuse, Muscadelle, Muscat Hamburg, Niagara, Noah, Olivette Blanche, Palomino (Napa Golden Chasselas), Pearl of Csaba, Rambola, Saint Emilion (Trebbiano), Semillon, Sau- vignon vert, Sylvaner, Thompson Seedless (Sultanina), Zinfandel. Varieties showing certain nontypical symptoms include Ribier, Feher Szagos, Alicante Bouschet, Mataro, Petite Sirah, Trousseau, Flame Tokay (Tokay), Mission, Thompson Seedless (Sultanina), Sultana, Muscat of Alexandria, Grenache, Catawba, lona. Pierce, Concord, and Zante Currant (Black Corinth). 32 University of California — Experiment Station Vineyards have been kept in good production by promptly roguing diseased vines and replanting with healthy vines. Replanting may be done by layering, approach-grafting to newly planted phylloxera- or nematode-resistant rootstoek, and by planting rootings or bench grafts. Pierce's disease may be confused with two other diseases, little-leaf and black measles. Little-leaf, a disease caused by zinc deficiency, is characterized by small leaves which develop varying degrees of interveinal chlorosis, asymmetry, and attenuation of the petiole sinus. The leaves at the tips of the shoots and canes are usually more severely affected than are those at the base. The canes usually produce numerous lateral shoots and the clusters often contain numerous small undeveloped seedless berries. Little-leaf may be controlled by applying zinc to the vine. Black measles is characterized by spotting, cracking, withering, and drying up of the fruit, by veinlet clearing, spotting, burning, and drop- ping of leaves, and by the new growth which usually develops after affected leaves fall. It is controlled by spraying or swabbing the old pruning wounds and the trunk with sodium arsenite. A table presents a seasonal comparison of the symptoms of Pierce's disease, little-leaf, and black measles. 20m-ll, '42 (36*26)