Disorders
Chlorosis
Chlorosis in grapes, particularly American varieties, is most frequently the result of iron deficiency in the plant. Excess calcium (high pH) in the soil makes the iron unavailable to the plants. In some areas of New Mexico, there also is an actual iron deficiency in the soil. Iron deficiency causes the leaves to turn yellow, while the veins and mid-ribs remain a normal green color. The yellow color of the leaves is due to a lack of chlorophyll, the green coloring matter important to the formation of plant sugars. Lack of chlorophyll, if left unremedied, decreases yield, reduces the sugar content of the fruit, and eventually kills the vine. Iron chelate, applied to vines twice during the growing season as a side-dressing, usually corrects the deficiency in good soil.
Little Leaf
Little-leaf may become a problem if the soil is highly alkaline or contains an excessive amount of calcium or organic matter. Grapevines affected with this disorder, a result of zinc deficiency, have stunted leaves. The first leaf formed on the shoot is usually normal or only slightly yellow. The yellowing becomes more severe as the shoot develops. The leaves at the base of the canes are green while those farther out on the shoot are smaller and more chlorotic. The tissue close to the veins is the greenest, with whitish or yellowish green areas between the veins. The most economical way to supply needed zinc is to daub pruning cuts with a zinc sulfate solution. Apply 1 pound of zinc sulfate, dissolved in 1 gallon of water (.45 kg in 7.6 l), to pruning cuts within two hours after pruning. Zinc foliar sprays are effective, but only if applied no later than two weeks before bloom. Zinc chelates also can be supplemented through the irrigation water.
Diseases
Botrytis Bunch Rot/Grey Mold/Noble Rot (Botrytis cinerea)
 Botrytis bunch rot, caused by the fungus Botrytis cinerea, is a common problem wherever grapes are grown. The disease can cause serious losses in both yield and quality when weather conditions favor the disease.
But Botrytis is a fungus which can both destroy a crop or bring it to glorious fruition.
When botrytis is handled properly, it creates the noble rot wines such as Sauternes and Tokaji - deliciously smooth and sweet. The story is that in 1650, a priest was making wine when an attack of the Turks delayed the harvest. When they realized fungus had grown on some of the grapes, they kept those separate, wondering how they would taste. They were quite pleased with the results! The Germans were next to follow, and then the French, where Sauternes became world famous for its delicious wines. Chateau d'Yquem is the best known creator of French Sauternes. The best grapes to create noble rot wines from include Riesling, Gewurztraminer, Semillon, Sauvignon Blanc and Chenin Blanc. Grapes must be harvested carefully, for the proper amount of fungal growth must be present on each bunch. Often harvests are done in several sweeps, picking out the correct grapes on each pass.
- Symptoms: Ripening grapes are affected by a rot which may progress to infect whole clusters. With sufficient rain and humidity, berries split open and develop a grayish mold on the surface. Affected berries may shrivel in the dry Okanagan climate. Botrytis may cause girdling lesions on the pedicel or rachis, leading to drying of clusters or portions of clusters, and premature cluster drop.
- Infection and Spread: Botrytis infects grape shoots, flowers, leaves and fruit under a range of temperature and humidity conditions. Infection is optimal at 15-20 oC with free water or over 90% humidity. Grape cultivars with dense canopies, thin skins, and/or tight clusters are more susceptible to botrytis bunch rot.
- Cultural Control of Botrytis Bunch Rot: During the growing season: Avoid overhead irrigation and keep irrigation periods as short as possible. Prevent excessive vine growth by judicious use of water and fertilizer. Canopy management, including shoot thinning and leaf removal before fruit set will reduce botrytis bunch rot. Remove leaves and lateral shoots located opposite, one node above, and one node below each fruit cluster. Prevent berry damage by effective control of powdery mildew early in the growing season. Minimize berry damage by birds and insects. During the dormant season: Knock mummified fruit and infected prunings to the ground and cover with soil, or alternatively burn.
- Chemical Control of Botrytis Bunch Rot: Fungicides registered for the control of botrytis include Rovral (iprodione), Vangard (cyprodinil), Elevate (fenhexamid) and Scala (pyrimethanil). These fungicides represent 3 different chemical classes. The number of spray applications necessary to control bunch rot depends upon disease pressure in the vineyard and weather conditions, as well as other factors such as susceptibility. Fewer applications may be needed if weather is very dry and/or disease pressure is low. Use a full program in vineyards where bunch rot was a serious problem in the previous year, and where sanitation measures were not taken after harvest. The number of sprays can be reduced or eliminated in vineyards with a history of low disease levels and for all vineyards in dry years. Key timings for botrytis fungicide applications are bloom, just before bunch closing, veraison and pre-harvest. Botrytis control becomes more difficult as the grapevine matures because heavy canopy growth and bunch closing make it difficult to place the fungicide where it is needed.
Powdery Mildew (Uncinula necator)
 Powdery mildew, also known as oidium, is caused by the fungus Uncinula necator. This fungus has a narrow host range attacking only grape plants and a few related species. It is the most common and widespread disease of grapevines in the Okanagan/Similkameen area. Popular wine grape varieties vary in susceptibility to powdery mildew such as:
- Very Susceptible: Bacchus, Cabernet Franc, Cabernet Sauvignon, Chancellor, Chardonnay, Chasselas, Gamay, Gewurztraminer, Himrod, Madeleine Angevine, Madeleine Sylvaner, Malbec, Muller Thurgau, Pearl of Csaba, Petit Verdot, Rkatzeteli, Riesling, Sauvignon blanc, Schonburger, Siegerebe, Syrah, Viognier.
- Somewhat Susceptible: Chelois, Chenin Blanc, Concord, Foch, Pinot blanc, Malbec, Merlot, Ortega, Pinot Noir, Perlett, Sheridan, Vidal Blanc, Weissburgunder
- Least Susceptible: Auxerrois, Malvoisie, Melon, Pinot Gris, Semillon
- Symptoms: Powdery mildew symptoms can be seen on foliage, fruit, flower parts and canes. Mildew usually appears first as whitish or greenish-white powdery patches on the undersides of basal leaves. It may cause mottling or distortion of severely infected leaves, as well as leaf curling and withering. Lateral shoots are very susceptible. Infected blossoms may fail to set fruit. Berries are most susceptible to infection during the first three to four weeks after bloom, but shoots, petioles and other cluster parts are susceptible all season. Infected berries may develop a netlike pattern of russet, and may crack open and dry up or never ripen at all. Old infections appear as reddish brown areas on dormant canes. Early powdery mildew infections can cause reduced berry size and reduced sugar content. Scarring and cracking of berries may be so severe as to make fruit unsuitable for any purpose. Be aware that many winemakers have a very low tolerance for powdery mildew on grapes. Research has shown that infection levels as low as 3% can taint the wine and give off-flavors.
 Life Cycle: The powdery mildew fungus overwinters as cleistothecia (tiny, round, black fruiting bodies), in bark, on canes, left-over fruit, and on leaves on the ground. Spores (ascospores) from the overwintering cleistothecia are released in the spring after a rainfall of at least 2.5 mm. For primary infection to occur the spores require at least 12-15 hours of continuous wetness at 10-15°C to infect developing plant tissue. Once primary infection has occurred the disease switches to its secondary phase. Secondary colonies (white mildew patches) form in 7 to 10 days, although the disease is not noticeable early in the season. The white patches of powdery mildew produce millions of spores (conidia) which are spread by wind to cause more infections. Free moisture is not needed for secondary infection; temperature is the most important environmental factor. The disease spreads quickly in early summer when temperatures are moderate. The incubation time (the time between infection and the production of spores) can be as short as 5 to 6 days under optimal temperatures.- Fungicides and Disease Forecasting: Start mildew programs before the overwintering fungus can infect new growth. The first few treatments are the most important, and should be applied starting at budbreak or early shoot growth. Protective fungicide treatments prevent infection of grape tissue by fungal spores. Good coverage is important. A mildew risk model can be used to forecast disease severity of secondary infections. The UC model developed at the University of California, Davis is the one most widely available and is sold with weather instrument software. For more information on powdery mildew forecasting models, refer to the University of California website at: http://www.ipm.ucdavis.edu/DISEASE/DATABASE/grapepowderymildew.html. If not using a disease forecasting model, apply powdery mildew control materials as frequently as necessary when severe mildew conditions exist.
- Cultural Control: (1) Select varieties that are less susceptible to mildew; (2) Manage canopies to increase air drainage and light penetration by removing lateral shoots in dense canopies. If necessary remove leaves in the fruiting zone. Dense canopies provide low light intensity, which favors powdery mildew development; (3) Use an under-vine irrigation system (drip or micro-jet); (4) Manage irrigation carefully. Excessive irrigation leads to excessive vigor and higher disease potential.
- Chemical Control: Protect grape foliage from primary infection by application of fungicides from early shoot growth until after bloom. Good control early in the season to prevent establishment of the disease is the key to preventing a powdery mildew epidemic later in the summer. Apply fungicides such as sulphur, Nova, Lance, Sovran, Flint or Milstop at the following growth stages: (1) When new growth is 5 to 10 cm long. (2) Just before or immediately after bloom. (3) Every 10 to 14 days until grapes begin to soften and red varieties begin development of color and white varieties change from green to white or yellow. If Kumulus (sulphur) is used, shorten the spray interval to 7-10 days. Dormant spray: Lime Sulphur is effective at suppressing the overwintering population of powdery mildew. It should be applied in early spring before bud break to dormant vines to kill powdery mildew cleistothecia (initial inoculum). Good spray coverage of dormant vines is important.
Sour Rot
 Sour rot has not been a commonly recognized problem in the Okanagan/Similkameen, but it was a serious issue in many vineyards during the 2004 growing season. Varieties which were affected include Pinot Blanc, Pinot Gris, Riesling, Pinot Noir and Chardonnay. It is likely that sour rot has always been present, but it may have been confused with botrytis bunch rot in the past. Sour rot affects both crop yield and wine quality. Infected fruit can give an unpleasant flavor to the finished wine and push volatile acid beyond acceptable levels.
- Symptoms: Symptoms include a soft watery rot with leakage of berry juice, and a distinctive vinegar smell. Large numbers of fruit flies, (also known as vinegar flies) and fruit fly larvae are generally present. The fruit flies produce ethyl acetate, a common fault in wine. There is very little tolerance of fruit contaminated with ethyl acetate. Sour rot appears similar to botrytis bunch rot. Affected berries are brick-colored in white cultivars and purplish-brown in red cultivars.
- Disease Cycle: Sour rot is caused by a number of undesirable yeasts and bacteria, often in association with other fungal rot diseases including Botrytis, Penicillium and Rhizopus. Sour rot pathogens gain entry into grape berries through cracks and wounds caused by wasps, hail, birds, powdery mildew, botrytis, or by berry splitting caused by excessive vigor in tight clusters. Such injuries attract fruit flies, which also effectively carry and spread the disease-causing organisms. During favorable conditions (warm moist weather, sugar accumulation in berries) the fruit fly will lay hundreds of eggs and start a new generation every ten to twelve days. Under the right conditions this can lead to explosive disease outbreaks. Fruit left on the ground from post-veraison bunch thinning can also be a contributing factor to build-up of fruit fly populations. Cultivars with tight clusters and thin skins are generally more susceptible to sour rot. Very vigorous vines seem to be more prone to the disease due to tighter bunches with berries more likely to burst, and also due to a higher moisture environment.
- Prevention and Control: (1) Reduce excessive vigor through the use of cover crops and/or the reduction of nitrogen fertilization and irrigation. (2) Leaf removal between fruit set and veraison can lead to tougher berry skins, thereby reducing the risk of lesions. (3) Control wasps through trapping and nest removal. (3) Control powdery mildew to reduce grape berry lesions, which attract fruit flies. (4) Prevent bird damage. (5) Bunch thinning is best done before or during veraison. Berries removed during late season thinning have higher sugars which can contribute to the fruit fly population increase. (5) Discard affected bunches before or during harvest to minimize the negative effects on the wine. (6) No insecticides are registered for the control of fruit flies on grape. Fruit flies quickly become resistant to most chemical control products due to their fast rate of multiplication. (7) Some French sources recommend 2-3 applications of Bordeaux mixture (copper sulphate and hydrated lime) at ten to twelve day intervals around the time of veraison. Copper applied to the fruiting zone has the effect of thickening the grape berry skin, hence reducing the risk of lesions. See fungicide notes under powdery mildew for more information on copper fungicides.
Downy Mildew
 Downy mildew is a major disease of grapes throughout the eastern United States. The fungus causes direct yield losses by rotting inflorescences, clusters and shoots. Indirect losses can result from premature defoliation of vines due to foliar infections. This premature defoliation 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: 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 up to 1/4 inch or more in diameter. 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. On 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.
- Organism: Downy mildew is caused by the fungus Plasmopara viticola. The fungus overwinters in infected leaves on the ground and possibly in diseased shoots. The overwintering spore (oospore) germinates in the spring and produces a different type of spore (sporangium). These sporangia are spread by wind and splashing rain. When plant parts are covered with a film of moisture, the sporangia release small swimming spores, called zoospores. Zoospores, which also are spread by splashing rain, germinate by producing a germ tube that enters the leaf through stomates (tiny pores) on the lower leaf surface.
- Cultural Control: Control Any practice that speeds the drying time of leaves and fruit will reduce the potential for infection. Select a planting site where vines are exposed to all-day sun, with good air circulation and soil drainage. Space vines properly in the row, and, if possible, orient the rows to maximize air movement down the row. 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.
- Chemical Control: A good fungicide spray program is extremely important. Downy mildew can be effectively controlled by properly timed and effective fungicides. For the most current spray recommendations, commercial growers use the sterol inhibiting (SI) fungicides (Bayleton and Nova) because have excellent post infection activity against powdery mildew. Ridomil and Aliette have excellent post infection activity against downy mildew. In dry growing seasons though, with few or no infection periods, a post infection program should result in reduced fungicide use. Mancozeb, Captan and Copper fungicides (fixed coppers and Bordeaux mixture) are highly effective for control of downy mildew. Ziram is moderately effective. All of these fungicides are only effective when used in a protectant spray program. They will not provide post-infection or curative activity and will not eradicate or "burn out" the fungus after symptoms appear.
Anthracnose
Anthracnose, caused by the fungus Elsinoe ampelina, is also known as bird’s-eye rot from its
appearance on the fruit. The disease appears first as dark red spots on the berry. Later, these
spots are circular, sunken, ashy-gray and in late stages these spots are surrounded by a dark
margin which gives it the “bird’s-eye rot” appearance. The spots vary in size from 1/4 inch in
diameter to about half the fruit.
The fungus also attacks shoots, tendrils, petioles, leaf veins, and fruit stems. Numerous spots
sometimes occur on the young shoots. These spots may unite and girdle the stem, causing death of the tips. Spots on petioles and leaves cause them to curl or become distorted.
Black Rot
Black rot is caused by a fungus, Guignardia bidwellii, which attacks the leaves, fruit, young canes, tendrils, and petioles. Black rot is seldom a serious disease, but it may become troublesome during seasons of frequent rains and high humidity. The symptoms of black rot are most conspicuous on the fruit and leaves. The leaf develops reddish brown spots, and immature berries develop brown spots that soon cover the entire berry, causing it to shrivel and mummify. Turn under or remove all mummified fruit and leaves from the ground and vines in late winter or early spring. Prebloom applications of fungicides are recommended where infections have been heavy.
Crown Gall
This bacterial disease is caused by Agrobacterium tumefaciens and is common on many other fruits, ornamentals, and trees. More or less spherical reddish-brown galls are formed on the roots. These can become as large as walnuts. They may be seen also on the stems above the ground as hard brown to black galls. When the galls or swellings caused by this disease are numerous the growth of the vine is affected. Soil fumigation, especially in nurseries, may be practiced as one means of control.
Dead Arm (Eutypa Dieback)
This disease, caused by the fungus Phomopsis viticola, kills the shoots and branches (or arms). It also attacks fruit and leaves. Most new-shoot infections occur before the shoots are 12 inches long. All parts of the shoots are subject to infection. New lesions are dark and eventually become elongated. Fruit infection, which is rare, causes a rot quite similar to black rot in appearance. The rotted tissue is not as 1 dark as black rot and the pycnidia are larger, but less numerous. Spores produced in pycnidia on the canes, arms or trunks, and on mummied berries, are dispersed early in the season and infections are usually limited to the first six or seven nodes. Trunk-infection symptoms are the most easily detected in June. The shoots from infected arms and trunks that were not killed during the winter are very much stunted. The leaves are small, crinkled, and yellow - especially at the margins. They cup upward or downward and the margins are ragged and irregular. The fungus enters the trunk and supporting arms through pruning stubs or breaks caused by winter injury. The fungus invades all portions of the wood. A cross section of the trunk may reveal a V-shaped section of darkened wood that extends toward the ground line. Affected shoots occur on either or both sides of the vine, depending on the location of the infected trunk tissue. Affected canes may die at any time during the year, but most die during the winter months. If the disease girdles the trunk, all upper portions die.
Vine Decline (Black Goo)
Vines infected by the Black Goo fungi Phaeoacremonium and Cylindrocarpon can appear normal for months or years. The fungi cause clogging of the water- and nutrient-bearing tissue, stunting growth or even killing the plant. The symptoms are many and varied: stunted growth, dark gummy ooze (black goo) instead of clear sap inside the wood, grooved and asymmetrical trunks, graft unions that fail to callus over, leaves that prematurely turn yellow. No effective treatment.
Pests
Nematodes
Nematodes are microscopic, multicellular, nonsegmented roundworms commonly present in soils. Roots of nematode-infested vines are unable to meet above-ground demands for nutrients and water. Vine damage is eventually manifested as reduced vigor and yield, with slight yellowing of leaves. Vine death seldom occurs unless there are other stresses on the plant. Root knot nematodes, dagger nematodes, and ring nematodes are the most common in vineyards. Plant parasitic nematodes are concentrated where feeder roots are most abundant. Therefore, when there is fear of nematode presence in the vineyard, sample both soil and roots in the berm area 12 to 18 inches from the vine trunk to a depth of 30 inches.
Root Knot
Root knot caused by a gall-forming nematode may become a problem in sandy and sandy loam soils, resulting in a decline in vine vigor and a reduction in yields. When planting new vineyards in nematode infected soil, use resistant rootstocks. In loam and clay loam soils, root knot is usually not a problem. In established vineyards with moderate root-knot infestations, effects of the disorder may be somewhat offset by more frequent irrigations during the main growing and fruit maturation seasons. Soil fumigation may become necessary.
Phylloxera
 Grape Phylloxera (Daktulosphaira vitifoliae, family Phylloxeridae, superfamily Aphidoidea) is a pest of commercial grapevines worldwide, originally native to eastern North America. These tiny, pale yellow sap-sucking insects, related to aphids, attack the roots of grape vines. The insects and secondary fungal infections can girdle roots, gradually cutting off the flow of nutrients and water to the vine. Nymphs also form protective galls on the undersides of grapevine leaves and overwinter under the bark or on the vine roots; these leaf galls are not found on vines grown in California.
In the late 1800s the Phylloxera epidemic destroyed most of the vineyards for wine grapes in Europe. Phylloxera was inadvertently introduced to Europe in the 1860s, possibly on imported North American vinestocks or plants. Because phylloxera is native to North America, the native grape species there are at least partially resistant. By contrast, the European wine grape Vitis vinifera is very susceptible to the aphid. The epidemic devastated most of the European wine growing industry. In 1863 the first vines began to deteriorate in the southern Rhône region of France. The problem spread rapidly across the continent. In France alone, total wine production fell from 84.5 million hecta-liters in 1875 to only 23.4 million hecta-liters. Some estimates hold that between two-thirds and nine-tenths of all European vineyards were destroyed.
The only European grape that is natively resistant to Phylloxera is the Assyrtiko grape which grows on the volcanic island of Santorini, Greece, although it is not clear whether the resistance is due to the rootstock itself or the volcanic ash on which it grows.
Use of a resistant rootstock, promoted by T.V. Munson, involves grafting a Vitis vinifera scion onto the roots of a resistant Vitis labrusca or other American native species. This is the preferred method today, because the rootstock does not interfere with the development of the wine grapes, and it furthermore allows the customization of the rootstock to soil and weather conditions, as well as desired vigor. Unfortunately not all rootstocks are equally resistant. In California, many growers used a rootstock called AxR1 which was thought to be resistant. Although phylloxera initially did not feed heavily on AxR1 roots, mutation and selective pressures within the phylloxera population eventually broke down its resistance, resulting in the failure of a number of vineyards, and the replanting of afflicted vineyards continues today. Many have suggested that this failure was predictable, as one parent of AxR1 is in fact a susceptible V. vinifera cultivar. Modern phylloxera infestation also occurs when wineries are in need of fruit immediately and cannot wait for grafted vines to be available.
Pierce's Disease
Just as mosquitoes deliver malaria to humans, a little insect known as the sharpshooter infects grape vines with the bacterium Xylella fastidiosa when they probe the leaves. The plants try to wall off the bacteria and end up choking off their own water and nutrient supply. It also afflicts other plants from almond trees to Oleander bushes planted along freeway median strips. There is no effective control.
Grape Berry Moths (Lepidoptera)
Grape-berry moths are small butterflies that lay eggs on grapes when blooming. The larvae first wrap the flowers up with a closely tangled web and then eat them or get into the grape destroying it.
- Angle Shades (Phlogophora meticulosa)
- Brown-tail (Euproctis chrysorrhoea)
- Endoclita signifer
- Garden Dart (Euxoa nigricans)
- Large Yellow Underwing (Noctua pronuba)
- Light brown apple moth (Epiphyas postvittana)
- Mouse Moth (Amphipyra tragopoginis)
- Setaceous Hebrew Character (Xestia c-nigrum)
- Turnip Moth (Agrotis segetum)
- Willow Beauty (Peribatodes rhomboidaria)
- Zenophassus schamyl
Grape Leafhopper
The grape leafhopper is a tiny insect less than 1/8 inch (1/4 cm) long. The adults are yellow with red and black markings on their wings. They spend the winter as adults in weedy, grassy areas near the vineyard and move into the vines as soon as growth begins. Eggs, which are laid in the leaves, hatch in about two weeks. The pale wingless nymphs (immature stage) feed on the lower surface of the leaves, casting skins five times before becoming adults. It takes three or four weeks for the young to reach the adult stage.
Grape-Leaf Skeletonizer
The western grape-leaf skeletonizer also becomes a problem, especially in small backyard or home vineyards. In the larva or worm stage, this insect is black and yellow (six-banded) and feeds only on the underside of the leaves. It eats the cells and leaves, but not even the smallest veins, creating a skeleton effect. When applying an insecticide, apply the material on leaf portions where insects are feeding.
Red Spider
The red spider is a mite that attacks leaves and ruins them by causing red spots. It winters inside the cracks of the bark, so it is fought in winter with oily preparations and in spring with sulphur pesticides.
|
There seem to be almost as many grapevine diseases and pests as grape varieties. Symptoms manifest themselves in many ways but generally, vines appear first to be wilting, vine growth is weak, and leaves are somewhat yellow/red with dried out leaf edges. In a more concealed method, roots die, diminishing the plant's ability to absorb water (and nutrients). Then, the plant wilts due to lack of water, and the dead leaves remain on the vines.
