Grape leaf blister mite

Nutrient deficiencies and toxicities can cause discoloration and deformation of vine leaves and shoots. Photo by Patty Skinkis, Oregon State University

Figuring Out Patterns

The pattern of symptom expression is often a key to understanding the nature of the disorder. Growers should try to answer these questions:

  • Are leaf symptoms on basal, middle, or apical leaves on a shoot?
  • Are symptoms on exterior or interior leaves only?
  • Are symptoms on some individual shoots or on all shoots of a vine?
  • Are leaf symptoms on leaf margins or some other distinct pattern?
  • Are vines with symptoms clustered together or scattered throughout the vineyard, or are they just on the edge rows or vines?
  • Are vines associated with any topographic character of the site, such as a swale or hilltop?
  • What is the time of year or growth stage when symptoms appear: spring as shoots are beginning to grow, early summer around flowering time, late summer as clusters begin ripening, or in fall at or after harvest?

Growers should document their observations with written notes and photographs, especially close-up photos of symptoms.

Summary

Grapevine disorders can be the result of both biological and abiotic factors. When determining the cause of a disorder symptom in the vineyard, it is important to consider all factors that could contribute to the problem. In some cases, the symptom may be caused by a chemical or fertilizer the grower has applied, or that drifting from a neighboring field. In other cases, the problem may be caused by an environmental pollutant or extreme weather. There are instances where a grapevine disorder can be remedied by grower intervention, but not all disorders will be within the control of the grower. Accurate and rapid diagnosis of a disorder is essential before a plan can be implemented to correct the problem and mitigate future recurrence.

Recommended Resources

Compendium of Grape Diseases. 1988. American Phytopathological Society.

Identifying Pests and Abiotic Disorders, University of California

Scouting Vineyards and Diagnosing Problems, Michigan State University

Grape Disease Management Overview

Herbicide Injury on Grapevines

Hail Damage on Grapevines

Sunscald Damage to Grapes

Frost Injury, Frost Avoidance, and Frost Protection

Monitoring Grapevine Nutrition

Grapevine Nutrition – online learning module and diagnostic tool

Integrated Crop Management of Grapevines PowerPoint, Michigan State University

Reviewed by Patty Skinkis, Oregon State University and Ed Hellman, Texas AgriLife Extension

Grape

Description

The Common or European grapevine (Vitis vinifera) is a long stemmed, woody vine (liana) which produces high value berries, or grapes. The vines can reach lengths in excess of 30 m and can live for many years with proper management. The leaves of the grape vine are alternately arranged on the stem and are long and broad with 5–7 lobes, typically reaching sizes of 5–20 cm (2.0–7.9 in). Flowers are produced in clusters and fruit. The fruit is a berry known as a grape and grows in clusters from the vine. In wild species, the fruit is 6 mm (1/5 in) in diameter and ripens to dark purple to black with a pale wax bloom. In cultivated plants, the berry is usually much larger, up to 3 cm (1.2 in) long and can be green, red or purple. Vitis vinifera is native to the Mediterranean region, central Europe, and southwestern Asia but is cultivated on every continent except Antarctica. Most grape cultivation centers on the use of Vitis vinifera, however, in North America the related species Vitis labrusca, Vitis riparia and Vitis rotundifolia are also grown. Vitis amurensis is native to Asia and has been hybridized with Vitis vinifera to produce cold tolerant grapevine varieties.

Cultivated purple grape
Young grapes
Nebbiolo grapes
Grape buds
Vineyard in Italy
Grape vine and trellis ‹ ×

Uses

Grapes are the most widely produced commercial fruit crop in the world. They are often eaten fresh but are also commonly used to produce wine. Grapes can also be processed into jams, and preserves, juices, grape seed oil, grape seed extract, raisins and vinegar.

Propagation

Requirements The first consideration when attempting to cultivate grape is to select a variety based on the prevailing local climate, with the best production occurring in hot, dry regions. American varieties tend to be the most cold hardy while the European hybrids perform best in hotter, drier regions. Generally, vines should be grown in full sun, in a well draining soil and in a location where there is good circulating air to reduce incidence of disease. Low lying areas should be avoided when selecting a planting site as this can lead to water accumulation during periods of wet weathe Vines prefer a soil with a slightly acidic to neutral pH between 6.0 and 7.0 and require a trellis system to support the weight of the fruit on the vines. Preparation Grape vines are usually planted as dormant bare root vines in Spring. Young plants can be purchased from nurseries and garden centres for planting in the home garden. Grape vines require a trellis and this should be built before the vines are planted in the ground. For information on constructing a suitable trellis see: https://www.plantvillage.com/posts/192-grape-how-to-build-a-trellis-for-grape-vines?locale=en. The trellis helps support the weight of the fruit and protects the vines from damage while aslo increasing air circulation and reducing diseases in the canopy. You may also consider a more decorative method of supporting the vines, such as an arbor. Planting New vines should be planted out in Spring after all danger of frost has passed. Dig a hole for each plant approximately 30 cm (12 in) deep and 30 cm (12 in) wide, spaced 1.8– 3.0 m (6–10 ft) apart and plant the vine at the same level as the nursery. It is important not to cover the graft union in soil. Tamp the soil around the plants and add any remaining soil. The newly planted vines should be cut back to have only 2 or 3 new buds and watered lightly. Training In order for grape vines to develop strong root systems and support heavy loads of fruit, new vines should not be allowed to produce fruit for the first 2–3 years after planting. The vine will produce new shoots, of which several should be allowed to grow while the others are cut back. This allows the vine to fill out with leaves which provide energy for an extensive root system. The new shoots should be attached to the trellis. At the beginning of the second year of growth, select 2–3 of the strongest canes on each plant and cut back the rest. Allow 3 or 4 shoots to develop on each cane and attach to the trellis. Remove any flower clusters that form. Pruning Pruning is an essential component of healthy grape production and should be carried out annually in early Spring while the vines are still dormant and before the buds begin to swell. From the third year onwards, most of the previous years growth should be removed. The more buds that are left on each shoot, the more fruit it will produce but care must be taken to ensure that too many are not left as the fruit may not ripen as a result. Fruit clusters can be removed as required throughout the growing season.

Grapes can be grown on arbors or porches
Grape trellis schematic for French grapes
Grape trellis schematics ‹ ×
CABI Crop Protection Compendium. (2014). Vitis vinifera datasheet. Available at: http://www.cabi.org/cpc/datasheet/56504. . Paid subscription required. Lord, W. (2001). Growing Grapes. University of New Hampshire Cooperative Extension. Available at: http://extension.unh.edu/resources/files/resource000576_rep598.pdf. . Free to access. Pearson, R. C. & Goheen, A. C. (Eds.) (1988). Compendium of Grape Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/40888.aspx. Available for purchase from APS Press. Strick, B. C. (2011). Growing Table Grapes. Oregon State University. Available at: http://smallfarms.oregonstate.edu/sites/default/files/publications/growing_table_grapes_ec1639_may_2011.pdf. . Free to access.

Ministry of Agriculture, Food and Rural Affairs

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Grapevine red blotch associated virus: A newly identified disease in vineyards

Grapevine red blotch associated virus (“red blotch”), a newly identified viral disease of grapevines, has received considerable media attention in the past few months. Grape varieties affected include not only reds, such as Merlot, Zinfandel, Mourvedre, Petite Syrah, Cabernet Franc, Cabernet sauvignon, Malbec, Pinot Noir and Petit Verdot, but also white varieties such as Chardonnay and Riesling as well as some table grape varieties and some rootstocks. The virus may be present in more varieties but the symptom expression may have more to do with the susceptibility of the particular grapevine variety.

Red blotch has been identified in many states and, in the past year, some vineyards in Ontario have been confirmed to be infected. These vineyards had historic difficulty maturing fruit. Researchers speculate that this disease has been “around” for a long time but has not been identified because the standard tests conducted for diagnoses weren’t specific to this type of virus. The only way to reliably test for this disease is through DNA sequencing specific to this virus.

Both leafroll and red blotch cause basal leaves in red varieties to turn red in late August through September. A diagnostic symptom of leafroll is that the veins stay green while the rest of the leaf turns red and roll downward. Red blotch does not cause leaves to roll, the red discolouration is blotchy and irregular and the smaller veins turn red rather than staying green. The symptoms in white varieties are much less distinctive. Infected vines have fruit with low Brix accumulation. In California, reductions of up to 5ºBrix have been reported in infected vines. Since it is relatively new, the impacts on Brix in cooler climates are not known at this time. In a Washington study, shoots on symptomatic vines of Merlot and Cabernet franc were 23 and 18% shorter than healthy vines at veraison and yield was 22 and 37% less, respectively. We also do not have information regarding the effect of red blotch on yield or vine cold hardiness or longevity under our climatic conditions.

The research community is still learning about this disease. We do know that the virus can be transmitted by grafting. California researchers indicate that in some commercial plantings, the virus has shown up over time in young, healthy vineyards next to old infected vineyards. There is some speculation that an insect vector could help spread the disease but there are no definitive answers at this time. Recent research in Washington has demonstrated that Virginia creeper leafhopper (also present in Ontario) is able to transmit red blotch virus from infected to healthy vines in greenhouse studies. Drs. Marc Fuchs and Greg Loeb, from Cornell University, are investigating potential vectors for this disease in eastern vineyards. From what we know about red blotch virus, it is highly unlikely that it can be mechanically transmitted by pruning, hedging, thinning and harvesting.

We don’t know at this point what threat red blotch poses to our industry. Since it has likely been here for a long time, identifying it is more likely to be an exercise in diagnosing vineyards with a history of low Brix to get an explanation for this problem rather than eliminating a source of inoculum. There are probably strains of the red blotch virus with different degrees of virulence. That means that even though a vineyard may test positive for the virus, it doesn’t mean the fruit yield or quality or vine health will be affected.

Removal of an infected vineyard is an economic decision – if the virus is present and significantly reducing Brix, a grower may decide to pull the block. CFIA’s position at this point is not to recommend removal of affected vineyards but rather to prohibit movement of propagation material from the vineyard. The removed vines should be burned on the site of the vineyard rather than being moved elsewhere.

The GGO and OMAF/MRA are conducting a preliminary survey of grapevine red blotch of 20 vineyards in Ontario. If your vineyard has persistent, inexplicable low or declining Brix levels and typical foliar symptoms of red blotch as described, please contact Wendy McFadden-Smith at [email protected]

For more information about red blotch, please go to the following web site:.

Fig 1: Potassium deficiency: Mid-shoot leaves lighten in colour, then turn purple and eventually brown spots appear along the margins of young blades. Leaf margins dry up and roll up or down, and blades become distorted and ruffled.

Fig 2: Grapevine leafroll virus: In late summer to early fall, diseased leaves turn reddish in red varieties or yellowish in white varieties, thicken and become more brittle. Leaves roll downwards starting at the base of the shoots. The leaf blade may be bright yellow or red, but the main veins remain green.

Fig 3: Grapevine red blotch virus: Blotches of pink or red veins on green leaves in the fall, when grape leaves would normally be turning a uniform gold color. Grapes are slow to develop sugar levels sufficient for winemaking, with some grapes never fully maturing. Infected vines tend to be smaller than uninfected ones.

Table grape growing, non commercial

Diseases

Powdery mildew

Powdery mildew is probably the most common disease of grapevines in the home garden. The disease becomes conspicuous as a grey/white powdery growth on all green parts, including leaves, shoots and berries.

Powdery mildew on grape vine leaves.

The berries may split and the pulp will often dry out. A fortnightly application of wettable sulfur or sulfur dust should be applied from mid September to late December. It is best to apply wettable sulfur early in the growing season and sulfur dust once the fruit has set. Do not apply sulfur on days when the maximum temperature is predicted to be 30°C or higher. Sprays containing bicarbonate of soda can also be used from early in the growing season to contain mildew.

Powdery mildew on grapes.

Downy mildew

This was was first detected in WA vineyards in 1998 but may not be a problem for the home gardener. The disease first appears on the upper surface of leaves as small yellow oilspots. The spots may enlarge to cover the leaf. A downy growth appears on the undersides of the oil spots.

As a preventive measure applications of copper oxychloride can be applied.

Pests

Bunch mites

Bunch mites are not visible to the naked eye. Adults are less than 0.2mm long and are found on the leaf underside close to the bunches. The mites damage the berry stalks by interrupting the water supply which causes the berries to shrivel and fall off. Do not confuse this with wind-suck which may happen in hot, dry windy weather as the roots withdraw water back from the berries as a method of survival.

Grape leaf blister mite

Blisters on a grape leaf

These mites cause blistering of the leaf on the upper-surface. On the under-surface felt-like patches develop. Although the leaves become unsightly, fruit production is not affected. A spray of lime sulfur applied at bud-swell should give adequate control.

Nematodes

The sandy soils on the coastal plain near Perth are known to contain root-knot nematodes (Meloidogyne sp.) which can destroy the root system of the vine as the vines get older. Table grapes grown on a nematode-resistant rootstock will perform much better than vines growing on their own roots but are harder to obtain through garden centres.

Grapeleaf blister mite

This is what damage by the grape erineum mite or grapeleaf blister mite, Colomerus vitis (Pagenstecher), looks like. We’ve found it in a few of our vines now that they’re bursting into life. It produces deformations of blister-like galls on the upper surface of the leaves and whitish patches on the underside.

This is inevitable, especially since we’re using no fungicidal or pesticidal treatments on the vines, organically-approved (copper and sulphur-based) or otherwise. We are removing clusters of infected leaves as we find them and will see what develops as the growing season progresses. This year I hope we’ll be able to devote more time to the vines, managing the canopy more effectively to minimise the effect of this and other vine diseases such as downy mildew (Plasmopara viticola) and harvesting at a more optimum time. We paid neither enough attention last year, which left us with a very low yield.

We’ll be removing leaves from around the ripening bunches of grapes to encourage more air flow and sun exposure and thinning shoots only where necessary. Last year we found that too much shoot thinning stimulated even more shoot formation!

For reference, here is a summary of the results of experiments conducted in Hungary in the 90s. There are some interesting conclusions, among which are that canopy management gives much the same results in terms of disease incidence and impact as conventional or organic spraying, and that the incidence of grey or noble rot (Botrytis cinerea) owed almost nothing to the management of the vines and everything to the rainfall patterns during the growing season.

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