Grape vine leaf diseases

Pest & Disease Control for Grape Vines

Every plant has the future potential for disease and insect damage. Factors such as location and weather will play a part in which issues your plants encounters. If available, disease-resistant varieties are the best option for easy care; and for all types of plants, proper maintenance (such as watering, pruning, spraying, weeding, and cleanup) can help keep most insects and diseases at bay.

NOTE: This is part 7 in a series of 11 articles. For a complete background on how to grow grape vines, we recommend starting from the beginning.

Downy Mildew

Yellow spots appear on leaves with downy spots on underside of foliage. Older leaves in center of vine are infected first. Can infect fruits, become soft, grayish, wither, may or may not have downy symptom. Over-winters on fallen leaves, so fall clean up is vital.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Copper Fungicide Spray or Dust

Chemical Control

  • Bonide® Fruit Tree Spray (berries only)
  • Bonide® Captan Fruit & Ornamental

Armillaria Root Rot

White knots between the bark and hardened at or below the soil line. Infected tissues have a mushroom-like odor when moist. Black fungus strands that look somewhat like roots, may be formed on the outside of the roots. During fall and early winter, fungus may produce mushroom-like fruiting bodies at the soil line around the trunk. Plant may die quickly or may show a slow decline with wilting leaves, and/or small dark green leaves. Disease progresses by root contact with infected plants. Soil fumigation may be necessary.

Control

  • Consult County Extension Agent

Scale

Usually on bark of young twigs and branches, encrusted with small (1/16”) hard, circular, scaly raised bumps with yellow centers, may also be on fruit. Sap feeding weakens vine.

Natural Control

  • Bonide® All Seasons® Horticultural & Dormant Spray Oil
  • Bonide® Insecticidal Soap
  • Bonied® Citrus, Fruit & Nut Orchard Spray

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Black Rot

Reddish-brown spots on leaves, spots soon appear on fruit, turn black. Then entire fruit becomes black, hard, shriveled mummy. Disease usually infects vine from bottom up. Over winters in fallen mummies (some mummies may cling on plant and can transmit disease also). Fall clean up is critical in control.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Copper Fungicide Spray or Dust

Chemical Control

  • Bonide® Fruit Tree Spray
  • Bonide® Captan Fruit & Ornamental

Botrytis Bunch Rot

May cause early season shoot blight following spring rains. Flowers can become infected during bloom. Then becomes dormant until sugar content of the infected berries increases later in the season. Infected berries split then leak and the fungus continue to grow. Intact ripe berries can be infected as harvest nears. Berries damaged by insects or birds are more susceptible. Removal of some leaves around the clusters can help control the disease. Don’t remove too many, especially on side that receives afternoon sun, to prevent sunburn of fruit. Fungus over-winters in berry mummies on ground and hanging on vine. Fall clean up is critical.

Chemical Control

  • Bonide® Fruit Tree Spray

Eutypa Dieback

Seldom seen in vines less than 8 years old. Most readily recognized symptoms are noticed during first 2 months of annual growth. They are malformed and discolored shoots, young leaves are small, cupped and often develop small necrotic spots and tattered margins. Grape clusters on affected shoots may have mixture of large and small berries. Symptoms become more extensive each year until part or the entire arm fails to produce shoots in the spring. Prune directly after a rain risk of infection is lowest at this time and prune late in dormant season to promote rapid healing. Spray or hand-paint large pruning wounds with fungicide soon after pruning and before rain.

Natural Control

  • Remove and destroy all infected wood.

Other Control Options

  • Consult County Extension Agent

Anthracnose (Bird’s-Eye Rot)

Black or brown lesions appear, especially on young leaves. Center of lesion becomes grayish-white and dries, may fall out giving a shot-hole appearance. May affect the shoots and the berries. Lesions on berries have dark brown or black margin, center is violet gradually becoming whitish-gray.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Copper Fungicide Spray or Dust

Appears as red blotchy areas on dormant canes. First appears on leaves as pale yellow or white spots on the upper surface. Soon a white webby substance appears and the white powdery masses. Fruit may be completely covered. Fungus may over-winter in dormant buds.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Black Measles

During summer or early autumn leaves on white varieties show yellow and red varieties show reddish patches, which enlarge and dry out. Severely infected leaves may drop and canes die back from the tip. On berries small round dark spots, bordered by a brown purple ring, may occur. Spots may appear any time between fruit set and ripening. In severely infected vines, berries may crack and dry on the vine. Believed to be caused by wood-rotting fungi that enter thru large pruning wounds. Occurs sporadically. Insect is more likely to occur in areas with consistently high summer temperatures such as California and Arizona.

Control

  • Consult County Extension Agent

Phomopsis Cane & Leaf Spot

Infected leaves have small, light green irregular or circular spots with dark centers. May be puckered along veins or margins may be turned under. May also have dark brown to black spots along veins and on leaf stems. Spots may drop out giving a ‘shot hole’ effect. Infected portions of leaf may turn yellow, and then brown and leaf may drop. Young shoots, fruit stems and leaf stems may have spots that enlarge and form dark brown or black streaks and stretches, which eventually crack leaving open wounds. The fungus also causes fruit to rot. The grapes gradually turn brown and shrivel. Infections are worse when vines are kept wet by rainfall for several days after bud break.

Natural Control

  • Serenade® Garden Disease Control
  • Bonide® Citrus, Fruit & Nut Orchard Spray
  • Remove as much diseased wood as practical by pruning.
  • Clean up all debris in fall.

Pierces’s Disease

The range of bacterium in wild vegetation that causes this disease extends from northern California southward in western US southward from latitude of Tennessee in the eastern states. It is not a problem where the bacterium is not established in the wild. Is transferred mainly by sharpshooter, leafhoppers and spittlebugs.
Chlorotic spots develop on leaves, discoloration intensifies and tissues begin to wither. In late summer drying spreads in concentric zones until entire leaf may be infected and drop, leaving the leaf stem attached to the vine. Late in the season, wood of infected canes show green ‘islands’ of tissues, surrounded by dark brown mature wood. Bud break in spring is delayed. First 4-6 leaves are small and tissues along major veins appear dark green against chlorotic background. Subsequent leaves are also small but normal in color. Affected vines may die the first year or may live for several years.

Natural Control

  • Plant resistant cultivars.
  • Some control achieved by controlling the sharpshooters, leafhoppers and spittlebugs.

Other Control Options

  • Consult County Extension Agent

Grape Leafhoppers

Adult is pale yellow with dark brown and reddish markings. Over-winters as an adult and found in spring on grape leaves and weeds. Lays eggs in tissue of leaves in April and May, which appear as bean-shaped blister-like bumps. When nymphs emerge they are almost transparent, later becoming white. Feeding from adults and nymphs causes pale yellow stippling on leaf. When populations are very high can cause loss of leaf efficiency and leaf drop, which weakens the vine for the following season. They have some natural predators such as green lacewings, lady beetles and some mites. Grape vines can tolerate high densities of leafhoppers.

Natural Control

  • Bonide® Insecticidal Soap
  • Bonide® Citrus, Fruit & Nut Orchard Spray
  • Remove weeds in vineyards and surrounding areas in spring.

Chemical Control

  • Bonide® Fruit Tree Spray
  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Omnivorous Leafroller

Adult is bell shaped, blackish gray snout-like mouthparts, forewings dark rusty brown with tan tips. Over winters in larval stage in mummified berries, in weeds and other trash. Moths emerge in spring and lay egg masses on leaves. Eggs hatch in 5 days and larvae tie two young leaves together to form nest in which they feed. Does not roll leaves. Later nests can be found in flower clusters and in bunches. Damage is not only from feeding on leaves, flowers and berries, but feeding sites allows rot organisms to enter fruit.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew
  • Bonide® Thuricide® Bacillus Thuringiensis (BT)
  • Control weeds

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Grape Leafroller

Over winters as pupae, moths emerge in April. May lay eggs singly on upper or lower leaf surfaces. Larvae are transparent. After hatching they feed for about 2 weeks between two webbed leaves. Then each larva rolls a leaf edge and feeds from the inside on the leaf edge. Then the mature larvae construct a separate leaf envelope in which they pupate. Early generations cause little damage, but generations later in summer can cause severe damage by complete defoliation to sunburned berries, soft fruit and direct feeding.

Natural Control

  • Bonide® Captain Jack’s™ Deadbug Brew
  • Bonide® Thuricide® Bacillus Thuringiensis (BT)

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Grape Mealybugs

Adults are 1/4” long, flat, oval shaped with a white waxy covering. Yellow to orange eggs are laid within an egg sac. Crawlers are yellow to brown in color. Over winters as an egg or very immature young in or near a white, cottony egg sac, under loose bark or in branch crotches, mostly found on north side of vine. They are not known to damage vines. Damage is by contamination of fruit clusters with egg sacs, larvae, adults and honeydew, which promotes growth of black sooty mold.

Natural Control

  • Bonide® All Seasons® Horticultural & Dormant Spray Oil
  • Bonide® Insecticidal Soap
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Chemical Control

  • Bonide® Fruit Tree Spray
  • Bayer Advanced™ Complete Insect Killer

Grape Cutworms

Caterpillars are dull colored with inconspicuous marks differing in different species. Varies from 1/2” – 2” in length. Many varieties of grapes can tolerate significant damage. Feeds on grapevines from bud swell till shoots are several inches long. Injured buds may fail to develop vines or clusters. Can cause yield reduction on varieties with unfruitful secondary buds. Problems are usually spotty or localized. Other insects cause similar damage. Cutworm feeding after shoots are several inches long does not result in significant injury.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Western Grapeleaf Skeletonizer

Adult metallic bluish or greenish-black moth emerges in early spring to June. Pale yellow capsule-shaped eggs laid in clusters on underside of leaf. Larvae feed side by side on underside of leaf. Five stages of larvae ranging from cream colored to brown to yellow with two purple and several black bands. Have conspicuous tufts of long black poisonous spine, which cause skin welts. When mature, larvae crawl under loose bark or in ground litter and spin a dirty white cocoon to pupate. Larvae feed on lower leaf surface leaving only veins and upper cuticle. This leaves a whitish paper like appearance. Later larvae stages skeletonize leaves, leaving only larger veins. Can defoliate vines by July and larvae may then feed on grape clusters causing bunch rot.

Chemical Control

  • Bonide® Fruit Tree Spray
  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Orange Tortrix

Adult is bell shaped about 1/2 “ long, orange colored, and has dark V-shaped marking mid wing. Caterpillars are straw-colored with a brown head, very active. When insect is disturbed they wiggle sideways or backward and either drop to ground or hang by silken thread. Overwintering larvae feed on vines, weeds and on any grape mummies remaining on vine. In spring feed on buds, canes and webbed leaves. Then enter bunches and make nests of webbing among the berries.

Natural Control

  • Fall clean up of weeds, dried grape clusters, harvest the fruit as early as possible.

Chemical Control

  • Bayer Advanced™ Complete Insect Killer

Grape Phylloxera

Adults are wingless females, generally oval shaped, less than 1/2” long, vary in color from yellow, olive green, brown or orange. Eggs are yellow and oval. Over winters as small nymphs on roots. In spring start feeding and growing. Damage occurs when insect feed on the roots, which swell and turn yellowish. Dead spots develop at feeding sites. If there are a lot of dead spots, vines become stunted and produce less fruit.

Natural Control

  • Plant resistant rootstock

Other Control Options

  • Consult County Extension Agent

Branch & Twig Borer

Adult females are dark brown beetles, cylindrical shaped, and males have white bodies, c-shaped with brown head. Males excavate tunnels where larvae spend up to 10 months. Adults burrow into canes thru base of bud or into crotch between shoot and spur. Infested canes can twist and break. Larvae bore into wood at dead and dying parts and feed. Not a significant problem in well-pruned vineyards.

Natural Control

  • Good cultural practices and clean up.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Grape Thrips

Small insects, less than 1/2” long, with feathery wings, yellow to brown in color. Cause damage if they lay eggs in fruit soon after bloom, scarring fruit. In summer they feed on new vegetative growth and damage summer foliage, not usually considered a problem. Avoid mowing cover crops infested with thrips before bloom or they may move to vines.

Natural Control

  • Bonide® Insecticidal Soap
  • Bonide® Captain Jack’s™ Deadbug Brew
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Grape Bud Beetle

Adults are light gray, about 1/4” long. Larvae stages are spent in the soil, adults emerge in mid-January to mid-March. Adults cause crop loss by feeding on opening buds and eating the bud center. After new shoots are 1-1 1/2” long, damage is negligible.

Control

  • Consult County Extension Agent

Grape Leadcable Borer

Adult is cylindrical black beetle, 1/4” long. Emerging from round holes in trunks of damaged vines and from dead wood in spring and early summer. Larvae are 1/3” long and cream color with dark head. Larvae are C-shaped and may be found in tunnels on the vine where they feed. Not a common pest.

Natural Control

  • Good sanitation practice.
  • Remove all pruning and dead wood.

Other Control Options

  • Consult County Extension Agent

Grape Vinegar Fly

Adults are small, yellowish flies and are attracted to fermenting fruit of all kinds. The larva is 1/4” long maggot shaped and can be found in damaged fruit. Eggs are laid in the exposed fruit tissues and emerging larvae feed on the berries. Main damage from the pest is sour rot organisms it carries from bunch to bunch. Any practice that reduces bunch rot will also reduce population of the vinegar fly.

Control

  • Consult County Extension Agent

Webspinning Spider Mites

There are several species of these mites. These pests range in color from amber to greenish to reddish to yellow, depending on the species and where on the vine it is located. As a result of feeding, dead spots appear on the leaves. High populations may cause leaf burning and prevent them from doing their work.

Natural Control

  • Bonide® insecticidal Soap
  • Bonide® Citrus, Fruit & Nut Orchard Spray

Chemical Control

  • Bonide® Fruit Tree Spray

Grape Flea Beetle

Flea beetles are approximately 1/10 inch long, shiny blue purple to blue green, with enlarged hind legs for jumping. Adult beetles damage primary buds when they feed on them and larvae feed on the leaves. Remove debris and leaf litter in and around grapevines. This will help to eliminate overwintering sites.

Chemical Control

  • Bonide® Fruit Tree Spray

Grape Berry Moth

Adult moth is small 6 mm long and brown in color. Eggs are laid singly on buds, stems and berries. Newly hatched larva is creamy white with a dark brown head then becomes greenish and eventually turns purple. Larvae feed on stems, buds and berries and often they feed inside protective webbings.

Natural Control

  • Fall clean up is important.
  • Bonide® Captain Jack’s™ Deadbug Brew

Chemical Control

  • Bonide® Fruit Tree Spray
  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

Japanese Beetle

Adult is metallic green beetle, which skeletonizes leaves. Larvae are a grub, which feeds on turf roots. Check turf product labels for timing of control of grubs. This is more of this problem is east of the Mississippi River.

Chemical Control

  • Bonide® Fruit Tree Spray
  • GardenTech® Sevin® Concentrate Bug Killer
  • Bayer Advanced™ Complete Insect Killer

In This Series

  • Introduction

Getting Started

  • Acclimate
  • Location
  • Planting
  • Soil Preparation

Care & Maintenance

  • Fertilizing
  • Pest & Disease Control
  • Pruning
  • Spraying
  • Watering

Other Topics

  • Harvesting

Treating Grapevine Problems: How To Take Care Of Grapevine Issues

Grapevines are tough plants that thrive after being severely cut back, re-bloom after snowy winters and produce masses of fruit even when neglected. That said, there are several pest, cultural and grapevine diseases that can minimize the vigor of these plants.

Rarely do grapevine pests or disease kill a vine, but it helps to have information on preventing problems in grapes so the harvest will be robust. Learn how to take care of grapevine issues and be prepared to apply treatments quickly.

Preventing Problems in Grapes

Grapevines have specific cultural requirements. When these are met, most vines perform beautifully with few problems. Grapes perform best if grown in well-drained soil with plenty of organic amendment. Most grape varieties are hardy in USDA zones 3 to 8, but some prefer cooler weather, while others need a longer warmer season.

Annual pruning is key to preventing problems in grapes. Train young canes to just one strong leader, with peripheral shoots coming off that and tied to a trellis.

Grapevine Diseases

There are many other grapevine diseases to be vigilant and prepared for treating grapevine problems, including both fungal and bacterial diseases.

Fungal – The

most common diseases of grapes are fungal. Much of these are controlled with good cultural control. Old plant material can harbor the fungal spores in soil even over the winter, so it is essential to clean up around the vines after pruning. Black spot, powdery mildew and anthracnose are just a few of the common fungal diseases. They most commonly affect the foliage with spotting or a coating, but may occasionally threaten twigs and terminal tissues. The fungus reduces the plant’s effectiveness at gathering solar energy and can cause leaf loss.

Bacterial – Bacterial grapevine diseases are also common in the plants. Where vines are growing in an orchard situation, the disease can be devastating as it passes from vine to vine. The home gardener is unlikely to experience this type of widespread damage. Crown gall disease in grapevines affects the roots and lower stems. The disease causes black galls and requires soil fumigation or solarization to kill the bacteria.

Grapevine Pests

The sweet, succulent fruit is a magnet for rodents, insects and especially birds. Bird nets can help protect the fruit from complete annihilation.

Sucking insects, such as aphids, will attack the terminal parts of the plant. Horticultural oils and insecticidal soaps, or neem oil, may be effective in combating common these types of insects.

Boring insects can seriously harm the health of your grapevine as well. Treating grapevine problems of this sort usually requires a pesticide registered for use on edible plants. Sevin is one recommended by the Texas A & M Agriculture department.

How to Take Care of Grapevine Issues

Treating grapevine problems starts with identification of the problem. There are so many potential pests and grapevine diseases that it might be helpful to collect a leaf or twig sample and take it into your county Extension office for identification.

Once you know what you are dealing with, it’s easier to decide how to proceed. Consider the difference between organic and inorganic. Organic fungicides and insecticides will be the choice for a natural gardener. Inorganic treatments are effective and the common choice for large-scale producers or gardeners that just want the job done.

No matter which treatment you choose, always read the label and apply in the manner recommended by the manufacturer.

Like any other plant species, grapevine is exposed to environmental influences, diseases and pests. There are several grapevine pests and diseases around the world. One of the most destructive vine pest in history was Grape phylloxera, who has damaged and destroyed several vineyards in Europe. It came to Europe from North America in late 1850s. Since American vines were resistant to those pests, winegrowers solved the problem by grafting European vines to American vines. Today you can find European-American grafting planted all over Europe.

One of the most common grapevine diseases and pests around the world are listed below.

Fungal diseases

Fungal diseases are the largest group of plant pathogens. After infection they spread around with the wind and the rain, insects and other organisms can also be transmitters. Signs of infection by fungi are freckles, necrosis, cover moldy, rotting and withering. Most common fungal grape diseases are: downy mildew, powdery mildew, gray mold, dead arm, and black rot.

Photo (Wikipedia): Fungal diseases – Powdery Mildew

Phytoplasma, virus and virus like diseases

Phytoplasmas are according to the cell structure similar to bacteria. They live in plant phloem tissue. Viruses are microscopic pathogens living inside the living cells. After entering into the vines they spread into all underground and above ground plant parts. In the nature, viruses are transmitted through vectors – insects, mites and nematodes. Changes that appear in the case of virus and phytoplasma diseases are: changes in the shape, size and color of lamina and changes on the vine shoot and clusters. Some of the most known phytoplasma vine diseases are: Flavescence dorée (FD), Bois Noir (BN), Grape leaf rust mite and Grapevine yellows (GY). Most common virus vine disease are: Feanleaf virus (GFLV) and Leafroll (GLRaV-1, GLRaV-2, …).

Photo (extension.org): Virus disease – Grape Leafroll Disease

Bacterial diseases

Bacteria are simple single-celled organisms that grow rapidly. They penetrate into the vines through natural openings of vines, or through vine wounds. Most common signs of bacterial infections are inflammation of the tissues and formation of cancer wounds. Most known bacterial vine diseases are: Happy disease, Crown gall and Pierce’s disease.

Photo (APS): Pierce’s diseases

Pests

Various pests are jeopardizing vines, but only some of them are responsible for economic losses. Most of them are insects, and in the less cases also mites and nematodes. Pests are making direct and indirect damage. They eat underground and above ground vines organs and are transmitters of fungal, virus and phytoplasma diseases. Pests that threaten grapevine are: butterflies, cicadas, scale insects, aphids, thrips, beetles, mites, etc. One of the most dangerous cicadas for grapevine is American grapevine leafhopper transmitter of Flavescence dorée.

Photo (green blog): Virginia creeper leafhopper

Source:
Different manuals for winegrowing

A few weeks ago my wife, Linda, made a special request. “Would you buy me a chain saw,” she asked.

When I asked why, Linda said she had to cut down the grapevines in the woods.

“They’re everywhere. They climb all the trees and kill them. I just want to cut the main stems at ground level,” she explained.

Grapevines

Linda clearly misunderstood the situation so I tried to explain. Grapevines do not kill trees. They are not parasites. They need trees to support themselves as they climb skyward to sunlight.

Furthermore, grapes are an important food for wildlife during the summer months. In fact, next to acorns and other nuts, it can be argued that grapes are the most important wildlife food in deciduous woods.

Food source

Bears, raccoons, opossums, skunks, and foxes are among the mammals that relish grapes. Game birds such as turkeys, ruffed grouse, bobwhite, and ring-necked pheasants frequent grape tangles when the fruits are ripe. And virtually all fruit-eating songbirds love grapes. That list includes catbirds, brown thrashers, robins, a variety of vireos and warblers, and even pileated woodpeckers.

Grapevine tangles also offer dense nesting and escape cover throughout the year. Catbirds and thrashers often nest in thickets overgrown by grapevines, and at least 16 species of songbirds use grapevine bark as nesting material.

In fact, I’ve never found a cardinal nest that was not made primarily of grape bark.
I rested my case, and Linda agreed to put off the purchase of a chain saw. “For now,” she said.

Climbing vines

Grapevines grow as woody climbing vines. Leaves are simple, large, heart-shaped at the based and often lobed.
Fleshy tendrils originate from the stems and grab onto tree branches to help the vine climb. As grapes ripen later in summer, they become dark blue or black.

Two other woody vines, one benign and one nasty, can be confused with grapes. Virginia creeper climbs like a grapevine and produces small, dark, grape-like fruits that are also important foods for wildlife. Its compound leaves typically consist of five small leaflets.
Poison ivy, a botanical chameleon, can grow as a vine, a shrub, or even a small tree. Its leaflets come in threes (hence the adage, “Leaflets three, let it be.”).

Finally, the surface of the leaves is always shiny, evidence of the oil (ursuhiol) that causes the rash. This irritating oil is present in all plant parts all year long, and it can remain active on dead plant parts for up to five years.

Poison ivy

Anytime you suspect you may have encountered poison ivy, wash the exposed skin with soap and water within two hours of exposure to prevent the urushiol from bonding to the skin.

With images of woody vines fresh on our minds, Linda and I spent Mother’s Day weekend along the Allegheny River in Foxburg, Pa. We were there for the annual Nature Fest, and on Saturday morning we scattered on field trips. One man in my group was Bill Paxton, a forester from Latrobe, Pa.

As we wandered the woods along the Allegheny River identifying birds, wildflowers, and trees it felt like a master class in natural history.

Sunlight

At one point Paxton pointed to a tall tree and said, “See how the tree provides access to the canopy for the grapevines? They need the sunlight.”
I then told Bill of my wife’s opinion of grapevines and asked if he could later give Linda a forester’s perspective.

When the morning field trips ended, I introduced Linda to Paxton. She spent the next 10 minutes learning about grapevines from an expert. He pleaded with her to appreciate grapevines.

“They’re just too valuable,” Paxton said.

Commercial value

He also added that grapevines can increase the commercial value of tall trees.

“When grapevines climb tall trees they sometimes prune side branches and leave behind longer, straighter, more valuable logs,” he explained.

But Bill also added that if grapes invaded the yard and aggressively climbed some favorite trees, it would be OK to remove them for aesthetic reasons.

Outweighing ecological value

That final concession did the trick. Linda agreed that the ecological value of grapes outweighed their aggressive nature.

“Cancel the chain saw order,” she said.

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Grapevine Leafroll Disease

Grapevine leafroll disease is caused by a complex of vector-borne virus species in the family closteroviridae. It is present in all grapegrowing regions of the world, primarily affecting vitis vinifera cultivars, hybrids, and rootstocks. The five serologically distinct pathogens associated with grapevine leafroll disease are known as Grapevine leafroll-associated viruses (GLRaV-1, -2, -3, -4, and -7). Of these, GLRAV-3 is the most widespread and damaging.

Diseased vines experience phloem degradation and decreases in net photosynthesis that affects fruit quality and pigmentation, delays maturity and reduces yield. Since there is no cure for the disease, planting virus-free vines and removing sources of virus from the vineyard are critical management strategies. Mealybugs and soft scale move GLRaV-3 from vine to vine; it is also transmissible by grafting. New developments include the use of hyperspectral imaging technology to remotely identify diseased vines.

Resources

UC IPM Guidelines for Virus Diseases

Grapevine Leafroll Disease – Cornell University

Mealybugs and Leafroll

Grapevine Pinot Gris Virus

Common symptoms of this disease include stunting, chlorotic leaf mottling, and deformation. These typical symptoms have been largely absent in Napa vineyards, even though the virus is present; this is because to date only “asymptomatic strains” of the virus have been found in California. Eriophyid mites of the erinuem strain have been implicated as vectors. As with other viral diseases, there is no recognized cure once a vine is infected.

Australian Wine Research Institute Fact Sheet

Grapevine Red Blotch Disease

Although recently “discovered”, there is evidence that Grapevine red blotch virus has been infecting California plant material since at least 1940. The virus interferes with grapevine metabolism; diseased vines remain essentially in a “juvenile” state with respect to ripening, and this affects both fruit and wine quality. The three-cornered alfalfa hopper (Spissistilus festinus) has been shown to transmit the virus under laboratory conditions; field studies are ongoing. Other membracids (Torstitilus spp.) that are morphologically similar to the alfalfa hopper are also being investigated as potential vectors. As with other viral diseases, there is no recognized cure once a vine is infected.

UC IPM Regional Pest Alert: Grapevine Red Blotch Associated Virus

UC IPM Video: “Grapevine Red Blotch: What You Need to Know”

UC Davis Grapevine Red Blotch Disease

UC Cooperative Extension: Grapevine Red Blotch Disease

UC Cooperative Extension: Photos of Grapevine Red Blotch Disease

Pierce’s Disease

Caused a bacterium and moved from vine to vine by spittlebugs and sharpshooters, Pierce’s Disease (PD) is episodic in the north coast region. During the most recent outbreak, incidence rates as high as 50-60% have been recorded in the most susceptible areas. Ongoing epidemiology studies seek to refine management strategies to lessen impacts. Newly released cultivars with PD resistance are being tested in field trials. Riparian revegetation (although costly) remains an effective way to manage the disease.

UC IPM Pest Management Guidelines: insect identification, disease symptoms and management

Xylella Fastidiosa Website

Photos of Pierce’s Disease

Photos of GWSS

PD/GWSS Board Useful Links

Powdery Mildew

Although a perennial concern for growers, grapevine powdery mildew (GPM) is generally controlled with preventative fungicide applications. However, continuous use of these compounds has resulted in the appearance of fungicide resistant populations of GPM in most US grape production regions. Growers suspecting GPM resistance as a factor in failed disease control can submit samples to a laboratory for analysis, or contact the UCCE Farm Advisor-Viticulture. Spore detection devices can be used to determine presence of GPM and adjust spray schedules accordingly.

NVG Viticultural Best Practices Video – Powdery Mildew (ENGLISH)

NVG Viticultural Best Practices Video – Powdery Mildew (SPANISH)

Trunk Diseases

Pathogens associated with the trunk diseases are characterized by their ability to infect woody grapevine tissue; diseases include Esca (measles), Eutypa dieback, Botryosphaeria dieback, and Phomopsis dieback. Symptoms range from spots or streaks on leaves, to distorted leaves and shoot stunting, and eventual death of spurs, arms, or cordons. Double pruning and pruning wound protectants are the most effective preventative practices. Economic studies have demonstrated that preventative practices are most beneficial when implemented before the vines show symptoms (early in the life of the vine).

Guide to Vineyard Trunk Diseases in California

UC IPM Pest Management Guidelines for Eutypa dieback, Botryosphaeria dieback, Phomopsis dieback, and Esca (Black Measles)

Powdery mildew of grapevines in Western Australia

Symptoms

The fungus causes ash-grey to white powdery growth on green tissue of the grapevine. In particular, the upper and lower surfaces of young leaves, shoots or clusters are highly susceptible.

The chains of conidia that develop from the powdery mildew hyphae give the infected vine tissue the characteristic powdery or dusty appearance. Severely infected vines emit a musty odour mid to late season.

Flag shoots are stunted shoots covered partly or wholly with ash-grey to white powdery growth with distorted leaves that curl upwards. These shoots become evident two to eight weeks after budburst (Figure 1).

Figure 1 A powdery mildew-infected flag shoot indicating cupped and distorted leaves (RW Emmett DEPI Victoria)

Leaves are most susceptible when they are expanding. Infections result in small yellow-green blotches 2-10mm in diameter with an irregular outline on the upper surface of leaves in spring (Figure 2). The blotches form an ash-grey to white powdery growth of hyphae which develops conidia on both sides of the leaf surface.

Web-like hyphae and chains of conidia are clearly visible with a 10x hand lens (Figure 3). In the field this fungal growth is flat, as the conidia chains are constantly broken. The blotches enlarge and may merge to cover the whole leaf (Figure 4). Smaller veins on the underside of the infected leaves may turn brown (Figure 5).

The earliest infected leaves become distorted and discoloured (Figure 6), sometimes giving the vines a wilted appearance. Severely diseased leaves blacken, dry out and fall prematurely in hot weather. Leaves become more resistant to infection with age, but are never completely resistant.

Figure 2 Yellow-green leaf blotches where early powdery mildew infection has occurred Figure 3 Chains of powdery mildew conidia viewed under a microscope (also referred to as conidiospores) Figure 4 Severely infected Chardonnay leaf showing ash-grey growth on the surface Figure 5 Veins on the underside of the leaf can turn brown when infected Figure 6 Distorted leaf with rolled margins caused by powdery mildew infection

Shoots – ash-grey to white powdery growth develops in patches until the whole shoot is covered (Figure 7). Severely diseased shoots are weakened, stunted and can die.

Figure 7 Shoot infection of powdery mildew showing colonies in a patchy distribution

Bunches of most cultivars are susceptible between flowering and up to five weeks later. Although berries develop resistance with age the bunch stalk and stems remain susceptible. Ash-grey to white powdery growth develops on immature berries and bunch stalks (Figure 8).

Severely infected berries may develop irregular shapes, crack or split and rot. Red varieties may colour unevenly. Post-veraison, berries develop a brown web-like pattern on the surface, very noticeable on white varieties (Figure 9).

Over time berries become resistant to powdery mildew infection and thus once this occurs the fungus is killed inside the berry leaving scar tissue on the berry. When the berry expands these scars can lead to berry split and a site for Botrytis cinerea infection.

Figure 8 Bunch of grapes with severe infection of powdery mildew Figure 9 Scarring of berries where growth of powdery mildew has occurred on the skin surface

Black patches on green immature shoots develop into reddish-brown patches on mature canes. This is evidence of a powdery mildew infection earlier in the season.

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