Grape Grapes are among the oldest cultivated plants in the world. Human history and grape culture have been intertwined for eons. Leading producers of grapes are: Italy, France, former Soviet Union, Argentina and U.S. California produces about 90% of US grapes Most grapes are used in wine production ~90% of raisin grapes are grown in Fresno County

Grape Family Vitis has 11 genera and 600 species Genus Vitis is the only food-bearing genus About 30 species are native to North America There has been much interbreeding to give rise to current cultivars **Images and lecture material were not entirely created by J. Bond. Some of this material was created by others.**

Economically important species Vitis vinifera -European grape—the basis of the world wine, raisin and table grape industries. Includes ‘Thompson Seedless’ V. labrusca (Fox grape) Blue grapes primarily used for juice ‘Concord’ is leading cultivar V. riparia (Riverbank grape) Blue grapes ‘Beta’, ‘Marechal Foch’, ‘Baco Noir’ V. aestivalis (summer, pigeon or winter grape) ‘Norton’ V. rupestris (rock or mountain grape) ‘St. George’ Muscadine grapes V. rotundifolia, V. munsoniana & V. popenoei

Principal grapes grown in North America European grapes—for wine, raisins and table use American blue grapes—for juice and jelly French American hybrids—primarily for wine in areas with cold winters Muscadine grapes—in the south

Grape vine anatomy Roots - Grapes root readily from hardwood cuttings. Most European grapevines are propagated on specific rootstocks Trunk - May be single or split. This is usually maintained as part of the perennial structure of the vine. It may be trained vertically or in a J fashion. Cordon - Horizontal permanent stems. Not all training systems have cordons Canes - One year old wood. May have 5-10 nodes. Current season growth is also called canes. Spurs - Canes pruned off short, usually 2-3 buds. May be fruiting spurs or renewal spurs Tendrils - Twining structures borne opposite leaves or clusters. Helps hold grapes to trellises

Diseases Crown gall Downy mildew Black rot Pierce’s disease

Crown Gall Caused by the bacterium Agrobacterium tumefaciens. This bacterium has the widest host range of any plant pathogen. It is capable of causing tumors, or "galls," on virtually all plant species, except the monocots. A similar bacterium, Agrobacterium rubi, causes galls on the canes of brambles Serious problem, freeze injury locations are worse. Rod shaped bacteria non-motile and motile., biovars –3 is found on grape

Crown Gall All fruit crops grown in Illinois are susceptible. The disease is particularly destructive on brambles (raspberries and blackberries) and grapes. It can also cause severe problems on apple, pear, blueberry, all stone fruits and on ornamentals. The bacteria induce galls or tumors on the roots, crowns, trunks and canes of infected plants. These galls interfere with water and nutrient flow in the plants. Seriously infected plants may become weakened, stunted and unproductive.

Symptoms The disease first appears as small overgrowths or galls on the roots, crown, trunk or canes. Galls usually develop on the crown or trunk of the plant near the soil line or underground on the roots. Above ground or aerial galls may form on canes of brambles and highly susceptible cultivars of grape. Although they can occur, aerial galls are not common on fruit trees. In early stages of development the galls appear as tumor-like swellings that are more or less spherical, white or flesh-colored, rough, spongy (soft) and wart-like.

Symptoms They usually form in late spring or early summer and can be formed each season. As galls age they become dark brown to black, hard, rough, and woody. Some disintegrate with time and others may remain for the life of the plant. The tops of infected plants may appear normal. If infection is severe, plants may be stunted, produce dry, poorly-developed fruit, or show various deficiency symptoms due to impaired uptake and transport of nutrients and water.

Symptoms Crown gall of grape

Disease Cycle The bacteria overwinter inside the plant in galls, or in the soil. The persists for long periods in the soil and plant debris. When they come in contact with fresh, wounded tissue of a host, they enter the plant and induce gall formation. The bacteria are most commonly introduced into a planting site on or in planting material. Wounds that commonly serve as infection sites are those made during pruning, machinery operations, freezing injury, growth cracks, soil insects and any other factor that causes injury to plant tissues. Bacteria are abundant in the outer portions of primary galls, which is often sloughed off into the soil. In addition to primary galls, secondary galls may also form around other wounds and on other portions of the plant in the absence of the bacterium.

Control Obtain clean (disease free) nursery stock, and avoid planting clean material in sites previously infested with the bacteria. Any practice that reduces wounding is highly beneficial. Preventing winter injury (especially on grapes) is also beneficial. On grapes, the double trunk system of training may be a useful system for minimizing losses due to crown gall. If one trunk is infected, it can be removed. Galls on the upper parts of the trunk or on canes can be removed by pruning.

Control A biological control agent for crown gall is available for apple, pear, stone fruit, blueberry, brambles and many ornamentals. It is not effective on grape. The agent is a nonpathogenic strain of bacterium (Agrobacterium radiobacter strain 84) that protects the plants against infection by the naturally occurring strains of pathogenic bacteria in the soil. Nursery stock is dipped in a suspension at planting time. The antagonistic bacteria act only to protect disease free plants from future infection by the crown gall bacterium; they cannot cure infected plants.

Downy mildew A major disease of grapes throughout the eastern United States. The causal agent Plasmopara viticola, causes direct yield losses by rotting inflorescences, clusters and shoots. Indirect losses can result from premature defoliation of vines due to foliar infections. This is a serious problem because it predisposes the vine to winter injury. It may take a vineyard several years to fully recover after severe winter injury.

Symptoms and Signs On leaves, young infections are very small, greenish-yellow, translucent spots that are difficult to see. With time the lesions enlarge, appearing on the upper leaf surface as irregular pale-yellow to greenish-yellow spots. On the underside of the leaf, the fungus mycelium (the "downy mildew") can be seen within the border of the lesion as a delicate, dense, white to grayish, cotton-like growth. Infected tissue gradually becomes dark brown, irregular, and brittle. Severely infected leaves eventually turn brown, wither, curl, and drop. The disease attacks older leaves in late summer and autumn, producing a mosaic of small, angular, yellow to red-brown spots on the upper surface. Lesions commonly form along veins, and the fungus sporulates in these areas on the lower leaf surface during periods of wet weather and high humidity.

Downy Mildew

Symptoms and Signs - Fruit Most infection occurs during 2 distinct periods in the growing season. The first is when berries are about the size of small peas. When infected at this stage, young berries turn light brown and soft, shatter easily, and under humid conditions are often covered with the downy-like growth of the fungus. Generally, little infection occurs during hot summer months. As nights become cooler in late summer or early fall, the second infection period may develop. Berries infected at this time generally do not turn soft or become covered with the downy growth. Instead, they turn dull green, then dark brown to brownish-purple. They may wrinkle and shatter easily and, in severe cases, the entire fruit cluster may rot. These infected fruit will never mature normally.

Symptoms and Signs - Fruit

Symptoms and Signs - Shoots and Tendrils Early symptoms appear as water-soaked, shiny depressions on which the dense downy mildew growth appears. Young shoots usually are stunted and become thickened and distorted. Severely infected shoots and tendrils usually die

Disease Cycle The fungus overwinters in infected leaves on the ground and possibly in diseased shoots. Oospores germinates in the spring and produce a sporangium. These sporangia are spread by wind and splashing rain. The sporangia release zoospores, which also are spread by splashing rain, either will produce a germ tube and enters through stomates. Once inside the plant, the fungus grows and spreads through tissues. Infections are usually visible as lesions in about 7-12 days. At night during periods of high humidity and temperatures above 55 degrees F (13 degrees C), the fungus grows out through the stomates and produces sporangiophores on the lower leaf surface. The small sporangiophores and sporangia make up the cottony, downy mildew growth. Sporangia cause secondary infections and are spread by rain. The optimum temp. for disease development is 64 to 76 degrees F.

Control Any practice that speeds the drying time of leaves and fruit will reduce the potential for infection. Sanitation is important. Remove dead leaves and berries from vines and the ground after leaf drop. It may be beneficial to cultivate the vineyard before bud break to cover old berries and other debris with soil. Cultivation also prevents overwintering spores from reaching developing vines in the spring. To improve air circulation, control weeds and tall grasses in the vineyard and surrounding areas. Grape varieties vary greatly in their susceptibility to downy mildew. In general, vinifera (Vitis vinifera) varieties are much more susceptible than American types, and the French hybrids are somewhat intermediate in susceptibility. A good fungicide spray program is extremely important. Downy mildew can be effectively controlled by properly timed and effective fungicides.

Black rot Caused by the fungus Guignardia bidwellii The the most serious disease of cultivated and wild grapes in Illinois and is one of most important disease of northeast US, Canada, EU, SA The disease is most destructive in warm, wet seasons. Crop losses range from 5 – 80% The fungus attacks all green parts of the vine – the leaves, shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the fruit.

Black Rot Infections early in the growing season destroy blossom clusters or cause developing berries to "shell off" the cluster and fall to the ground. Later infection periods can destroy a high percentage of the berries, turning them into hard, black, shriveled "mummies." Unsprayed fruit on very susceptible varieties may become almost completely rotted by harvest time

Symptoms - Leaves Reddish brown and circular-to-angular spots appear on the upper surface of the leaves starting in the late spring. As spots coalesce, they form irregular blotches that are reddish brown. The number of spots or lesions per leaf varies from 1 to more than 100 The center of the leaf spot turns tannish brown and is surrounded by a black margin. Pycnidia that are speck sized and black are arranged in a definite ring just inside the margin of the spot. Only young, rapidly growing leaves are susceptible.

Symptoms - Leaves Black Rot

Symptoms - Fruit Fruit infections can take place shortly after the calyx (flower petal) falls, but most infections occur when the fruit is half to almost full size. A small spot appears that is circular and whitish tan, often surrounded by a brown ring. The spots rapidly enlarge, darken, and may cover half or more of the berry within 48 hours. The center of the spot rapidly becomes sunken, wrinkled, and dark. Within a few days, the entire berry becomes coal black, hard, and mummified. The diseased fruit 'shell' or shatter and drop early. The surface of the withered fruit is covered with minute, black pycnidia that are often arranged in circular zones.

Symptoms - Fruit Black Rot

Symptoms - Shoots, Leaf and Fruit Stems, and Tendrils The lesions on these parts are dark purple to black, oval to elongated, and somewhat sunken. The speck-sized black pycnidia are scattered over the surface of the lesions. As the canes grow, the bark tends to split along the length of the lesion. If the berry stem is infected early, the flow of sap is shut off, and the berry shrivels and fails to develop.

Black Rot

Disease Cycle Overwinters in canes, tendrils, and leaves on the grape vine and on the ground. Mummified berries on the ground or those on vines become the major infection source the following spring. During rain, ascospores are shot out of numerous, perithecia and are carried by air currents to young, expanding leaves. Ascospores slowly germinate, often taking 36 to 48 hours, penetrate the young leaves and fruit stems (pedicels). The infections become visible after 8 to 25 days. Spots appear first on the lower leaves. When the weather is moist, ascospores are produced and released throughout the entire spring and summer, providing continuous primary infection. The fungus requires warm weather for optimal growth; cool weather slows its growth. A period of 2 to 3 days of rain, drizzle, or fog is also required for infection.

Disease Cycle Each older leaf spot contains a number of pycnidia, each of which produces hundreds of summer conidia that ooze out in winding tendrils during wet weather. Raindrops spreads these spores to other leaves and to young fruit. The conidia germinate in 10 to 15 hours and penetrate young tissue. New infections continue into late spring and summer during prolonged periods of warm, rainy weather. The conidia are capable of germinating and causing infection several months after being formed. During August, the pycnidia are transformed into an overwintering sclerotia that, in turn, gives rise to perithecia which produce ascospores in the spring.

Control Space vines properly and choose a planting site where the vines will be exposed to full sun and good air circulation. Prune the vines each year during the dormant period. Remove the prunings, excess growth, diseased and overwintering berries, leaves, and tendrils Keep the fruit planting and surrounding areas free of weeds and tall grass. Where feasible, cultivate the vineyard before bud-break to bury the mummified berries. Use protective fungicide sprays, which are needed in wet seasons, to protect the developing new growth.

Pierce's Disease A lethal disease caused by the bacterium Xylella fastidiosa First detected in 1880s when it decimated vineyards in the LA Basin and again in the 1930 and 1940s. Pierce's disease is only known from North America through Central America and has been reported from some parts of northwestern South America. It is present in some California vineyards every year, with the most dramatic losses occurring in Napa Valley and in parts of San Joaquin Valley. During severe epidemics, losses may require major replanting.

Pierce’s Disease

Pierce's Disease The bacterium that causes Pierce's disease lives in the xylem and is spread from plant to plant by sap-feeding insects that feed on the xylem. Symptoms appear when a significant amount of xylem becomes blocked by the growth of the bacteria. Insect vectors for Pierce's disease belong to the sharpshooter and spittlebug families. The blue-green sharpshooter the green sharpshooter and the red-headed sharpshooter are important as vectors of this disease. Other sucking insects, such as grape leafhoppers, are not vectors.

Pathogen in Host Bacteria in xylem

Voracious, aggressive flyer and feeds and breeds on 133 host Spreads Pierce’s disease with astonishing speed. Vector of causal agent of Pierce’s Disease

Spring Symptoms In vines that are infected in spring, symptoms of Pierce's disease first appear as water stress in midsummer, caused by blockage of the water-conducting system by the bacteria. New leaves on PD vines are stunted, more yellow than normal, and deformed in shape. Interveinal areas of leaves may be more yellow than normal leaves, much like zinc deficiency symptoms.

Spring Symptoms Pierce’s Disease early symptoms

Summer Symptoms The combination of these three symptoms is a definitive indication that PD is present: 1) Leaves become slightly yellow or red along margins in white and red varieties respectively. As the disease advance leaf margins progressively dry or die (turn brown) in concentric zones. 2) Scorched leaves dry down and the blade falls, leaving the petiole attached to the cane. 3) Wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark.

Symptoms Thompson Seedless - Pierce’s Disease

Type and extent of symptoms vary: 1. Grape variety Highly susceptible are Barbera, Chardonnay, Fiesta, and Red Globe. Less susceptible varieties are Chenin blanc, Flame Seedless, Riesling, and Thompson Seedless. Cabernet sauvignon, Merlot, are intermediate" in susceptibility. 2. Date when the vine was infected. 3. Vine age -   The younger the vine, the faster severe symptoms will appear and the less chance that it will recover over the next winter. 4. Climate 5. "Variability".    For unknown reasons, different vines of the same age, location, and variety will develop somewhat different symptoms. 6.Other constraints mimicking Pierce's Disease Zinc deficiency, measles, salt burn

Control Removal of wild grapevines, immaculate weed control and establishing a weed-free perimeter around a vineyard provide the best strategy to manage Pierce’s disease. Sharpshooters need water to survive and reproduce. Avoiding sites adjacent to creeks, streams, ponds or even depressions that retain rainwater will reduce the likelihood of consistently high leafhopper populations. By creating a large (at least 150 ft.) buffer zone around vineyards, growers can either chemically or mechanically create an environment that is not favorable to insect populations. Growers should also understand that when hay fields adjacent to a vineyard are cut, large numbers of insects will be seeking alternative habitat and feeding sites. Insect monitoring and insecticide applications should be considered when insects move into the vineyard.