Pests of Grapevines

This pest has decreased in importance as producers have switched to drip irrigation systems.

Black vine weevil generally overwinters in the immature, larval or grub stage. The young larvae feed on small roots and root hairs. Larger larvae feed on larger roots, quite often within a few inches of the crown. The larvae change to inactive pupae and remain in earthen cells 3 to 4 inches below the ground in mid-April. The first adults emerge about May 20, and emergence peaks about June 20. All black vine weevils are females; males are not known. Each weevil is capable of laying 300 to 500 eggs. The first eggs are laid about 3 weeks after the adults emerge. Therefore, a grower has about three weeks from the time the first weevils emerge until controls must be applied.

The adult is a black-snouted beetle approximately 1/2 inch long (12.7 mm), having small gold patches on the fused wing covers. The beetle cannot fly. Adult beetles feed on grape clusters during June and July. Damage consists of girdled berry stems or cluster stems. Severely injured clusters have berries that do not size or ripen properly. Occasionally berries or parts of clusters are chewed off. Weevils are active and do most of their damage at night. They return to the ground at daylight to hide under clumps of soil, debris, or loose bark at the base of the plant. Therefore a weevil population may go undetected for a long time.

Registered synthetic pyrethroid insecticides can be applied as rescue treatments if infestations are severe. Direct insecticide sprays at the crown (base of the vine) and up several feet from the soil surface. Pyrethroid insecticides are biologically disruptive and can cause populations of secondary pests, including spider mites, to flare.

In the eastern United States, Brown Marmorated Stink Bug (BMSB) is an invasive insect that has had severe economic impacts on numerous commodities. BMSB was discovered in the Pacific Northwest several years ago. It has not yet been a problem in commercial vineyards because the population sizes remain relatively low in eastern Washington. Western Washington has higher populations, yet no vineyards have reported infestations.

There are many native stink bugs that look similar to BMSB, yet the combination of these three key characteristics can distinguish BMSB:

• light and dark bands on the antennae
• smooth “shoulders” with no spikes
• dark and light bands around the abdominal margins.

Pictures and additional descriptions of each life stage can be found in the Field Guide for Integrated Pest Management in Pacific Northwest Vineyards (PNW644) or https://www.stopbmsb.org/. If you detect BMSB in your vineyard, please contact your local extension office or research center.

Specific chemical management is not recommended for BMSB.

Cutworms are the larvae, or wormlike stage, of nightflying gray to brown moths. Several species or kinds of cutworms cause injury in vineyards.

Cutworms and related species usually overwinter as partially grown (2nd or 3rd instar) cutworms in the soil, or under debris in the vineyard. Young cutworms begin feeding on winter annual weeds, particularly mustards, during warm periods in February and March. By the time of bud break they are nearly full grown. They remain under cover (within cracks in soil or plant debris, or under rough bark on trunks) during the day, but climb the vines to feed on buds or shoots at night—or on cloudy days when light levels are low.

Euxoa spp. cutworm types overwinter as eggs which hatch about April 10. Young larvae may climb vines and feed on buds or shoots. Some years cutworm injury can begin in late March or early April (spotted cutworm) and continue through May into early June (redback cutworm). Damage to newly planted vines may mean loss of shoot growth (nothing to train) or death of the plant; damage to older vines may cause fruit production losses. Cutworm damage is often intensified by discing the cover crop in early May.

Cutworm Management

Sampling for spotted cutworms before or at the time of bud break is very difficult. Therefore, growers may wish to make prophylactic applications of pyrethroid barrier sprays targeted towards the base of the trunk for cutworm control based on one of the following criteria:

1. Since early season cutworms are difficult to find and injuries caused by 2nd or 3rd instars are small, the decision to spray may be based on the recent history of the vineyard. Usually, cutworm problems in established vineyards occur in the same portions of a vineyard each year. In those cases, a prophylactic application of a synthetic pyrethroid as barrier may be warranted.
2. A synthetic pyrethroid barrier should be sprayed at sufficient concentrations and directed in sufficient volume of water to cover the trunk of the vine from just above the soil surface to a height of between 16 and 18 inches. Red-eye sensors that control spray volume and discharge a targeted spray at only the base of trunks and vineyard posts are the most efficient method of applying the barrier sprays. Begin control in the delayed-dormant (wooly bud) period, just before buds start to swell. If the treatment is for cutworms alone, direct spray to the trunks, wire, and posts leading from the ground to the cordons.
3. Inspect vineyards carefully for presence of cutworms. The best method is scouting trunks and cordons after dark by flashlight. Injured buds may be an indication of spotted cutworm injury (late March–early April). Injured buds and new shoots may be caused by large spotted cutworms (mid-to late April) or redback cutworms (late April to early June). Apply sprays when bud injury reaches 5% to 10% of the total bud crop. Base sprays for shoot or cluster bud injury on the amount of injury and economics.
4. Newly planted vines need special protection. Frequently the disturbance of weeds or other cover in the planting process leaves little food for resident cutworms. Since there may only be a few buds on a young plant, injury by cutworms may be severe. Registered synthetic pyrethroid insecticides can be applied as rescue treatments if infestations are severe. Pyrethroid insecticides are biologically disruptive and can cause populations of secondary pests, including spider mites, to flare.

Drosophila suzukii, also known by the unofficial common name of spotted wing drosophila (SWD) is a problem for many berry growers, but does not appear to affect undamaged grapes and does not warrant specific control.

D. suzukii invaded all Washington State grape producing counties in 2010. It is a vinegar fly, but unlike other common and ubiquitous vinegar flies, it has a serrated ovipositor used to puncture undamaged fruit and lay eggs. We have direct observation of it infesting ripening cherry, raspberry, blueberry, and apricot; it has also been observed attacking other soft-flesh fruit such as nectarines, peaches, and volunteer fruits including blackberry and hawthorn.

Populations or prevalence of D. suzukii is greatly influenced by temperature. In Eastern Washington, populations have generally remained low in the early and mid-season when temperatures are exceeding 90°F, yet populations rise later in the season when daytime temperatures are cooler. In Western Washington, where temperatures can be more moderate, populations can build through the season. In other grape growing regions, specific thin-skinned grape varieties can be infested by D. suzukii.

Caution should be taken if vineyards are established with thin-skinned varieties.

Vinegar, or fruit flies, as a general species (Drosophila sp.). are implicated in the spread of the sour rot complex. Their feeding on fruit can help spread the associated microbes. As such, while we don’t typically recommend management of fruit flies in Washington vineyards as a direct pest, their management may be needed in vineyards with a history of late summer and early fall sour rot.

The grape flea beetle, Altica chalybea, is rarely a pest in the PNW but populations can develop that defoliate newly planted, non-bearing vineyards in mid to late spring, especially when grow tubes are used on young vines.

Grape flea beetles are shiny metallic blue and about 3/16 inch (4.8 mm) long. They have long antennae and swollen “thighs” (i.e., femora) on their last pair of legs. When the adults are disturbed they jump; hence the name flea beetle. The larvae are extremely cryptic and typically not observed. The adults are highly clustered in their distribution within a vineyard and can be observed in substantial abundance.

Larvae and adults feed on the upper and lower leaf surfaces producing a skeletonized or lacey appearance, although this injury is usually not serious. The most serious damage occurs in the spring as the larva emerge from overwintering sites and feed on newly swollen grape buds. The adult beetles chew holes in the sides and ends of the buds often hollowing out the whole bud only leaving the overwintering scleritized bud sheath. Their feeding damages primary and occasionally secondary and tertiary buds and can be confused with cutworm damage. However, cutworm damage tends to be more apparent and occurs on multiple swelling buds on an individual vine. Flea beetle damage to buds in mature vineyards is more sporadic than cutworm damage and less severe after buds have grown to 1/2 inch (12.7 cm) or more. Young plants can sustain more damage even through mid-summer.

Monitoring for flea beetle should be done in conjunction with cutworm monitoring. Because of the similarities in feeding, the cutworm protocol should detect populations of grape flea beetle adults and their damage.

Control is most important in newly-established vineyards and typically not recommended on mature vines. Insecticides will reduce adult populations. Vineyards infested with flea beetle populations the prior season should be monitored rigorously in spring to control the larvae.

Current recommendations are to apply insecticides for larvae if more than 4% of buds are damaged in young vineyards.

A species of grape leaffolder, Desmia maculasis, has emerged as a pest in several AVAs in Washington state. It is a close relative to another grape leaffolder species that is an occasional pest in California, Desmia funeralis.

Research is ongoing in Washington state to determine economic injury and a potential economic threshold for Desmia maculasis.

Damage from Desmia funeralis activity after fruit set is rarely a concern; in California, 20% damage to leaves has been observed without damage to fruit quality or ripening. Damage to yields may occur if severe leaffolding occurs before and during bloom, which would restrict photosynthesis. Only treat for leaffolders if extreme damage resulting in crop loss has occurred in the past.

If necessary, treatments should be applied as soon as the first leafrolling is noticed; small larvae are more susceptible to chemical intervention than instars.

Grape mealybug is the primary vector for the complex of several viruses that are the causal agents for grapevine leafroll disease (GLRD).  A secondary contamination can occur in late-season vineyards when the honeydew excreted by mealybugs drips on the foliage, twigs, and fruit. Sooty mold, a black fungus, may grow on this honeydew, producing a sooty appearance. Serious contamination can destroy the market value of the crop for processing.

Adult grape mealybugs are about 1/4 inch (6.35 mm) long, pink to dark purple, and covered with a white waxy powder. Strands of the wax extend from the body. Eggs are yellow to orange and are laid in cottony egg sacs. Crawlers are tiny, 1/16 to 1/8 inch (1.25–3.1 mm) long, pink to tan, and quite active.

Mealybugs overwinter as eggs or crawlers in the egg sacs, usually in the bark cracks or under the bark scales on the trunk and in the arms or cordons. In the spring, crawlers move quickly to new growth to feed. They mature in June, and adults move back to older wood to lay eggs. A second generation of crawlers will move to new growth, including the fruit, where they mature through July and August. The honeydew produced by this generation may contaminate fruit. A Grape Mealybug Lifecycle model is available on Grape DAS, and includes information as to when each lifestage is present. 

Grape mealybugs migrate from the clusters back to the cordons and main trunk between mid-August and mid-September. Late summer spray applications for mealybug control are usually ineffective. If large amounts of honeydew or honeydew and sooty mold are present on the fruit, a fungicide application may aid in disease suppression. Mealybugs will not exude honeydew after leaving the cluster.

Insecticide Program Approaches

To assist in timing insecticide applications, it is recommended to either use the Grape DAS Mealybug Model, or to use pheromone lures in the vineyard to track when male flights are peaking. You can use the information on DAS in regards to male mealybug flights to interpret your pheromone trap counts.

Several companies have marketed pheromone lures (e.g., Trece) for grape mealybug. Our data indicates that traps should be placed in a density of at least 1 trap per 40 acres. Traps should be placed out in vineyards in late April. Specifically males are attracted to these traps. Males seeking mates begin to fly in late April and flights peak in late May to early June. These pheromone traps are specifically a useful tool for determining which vineyard blocks have the greatest abundance of mealybugs. These blocks should then be field-scouted directly to determine if the mealybug population abundance warrants further control actions. Insecticides targeting the summer generation of mealybug crawlers should be applied 1 to 2 weeks following peak flights and trap capture of males.

Japanese Beetle (Popillia japonica) is a quarantine pest in Washington State.

For information on how to scout for the beetle (including trapping), and what to do if you find the it, please visit the Washington State Department of Agriculture’s Japanese Beetle website.

There are two stages of Japanese Beetle development that are commonly targeted for control:

1. Grub / larval stage – The ground / soil needs to be treated, typically from late fall to late spring.
2. Adult beetle stage – The plants on which the adults are actively feeding are treated. This stage is typically present mid-summer.

The adult beetle stage is the stage that will most likely be found in vineyards, in mid to late summer. In eastern Washington vineyards, given the high level of soil disturbance and lack of living vegetation under vines and between alleyways, it is unlikely the grub / larval stage will actively overwinter in there in large numbers.

Please also see WSU’s Guide for Japanese Beetle Management in Commercial Crops (Apples, Grapes and Corn).

Two species of leafhoppers can be common in Washington State vineyards. These include the western grape leafhopper and the Virginia creeper leafhopper. In reports greater than 10 years old, the western grape leafhopper was the predominant species in Washington State. However, in recent surveys, the Virginia creeper leafhopper has become the predominant leafhopper in Washington vineyards. Recent research in Northern California has demonstrated that the endemic parasitoid guild that biologically regulates populations of western grape leafhopper are mostly ineffective against the invasive Virginia creeper leafhopper. We have no empirical evidence for this in Washington State, but this may account for the species replacement of the western grape leafhopper by the Virginia creeper leafhopper in Washington State vineyards in recent years. Leafhopper adults and nymphs generally feed on shaded leaves. In heavy infestations, they may move to sun leaves. In addition to causing leaf injury, some leafhoppers may secrete honeydew, which contaminates fruit.

There are two generations per year. Adults spend the winter in the vineyard on the fallen leaves and trash under the vines. They become active when the weather becomes warm in March or April, feeding on weeds and wild hosts until young grape leaves appear. Overwintering adults lay eggs in the leaf tissue on the underside of the leaf. Eggs hatch from mid-May to the end of June. New adults are active by the middle of June. Eggs of the second generation are laid in early July. These hatch by mid-July; adults are active on the vines until late fall.

Control is most effective if you treat vines when the leafhoppers are in the immature, nymphal stage. Most leafhopper infestations are clustered in a vineyard. Spot specific treatment of Concord vineyards may be recommended, since most infestations are rarely of economic proportions on Concord. Young wine grape vineyards or wine grape vineyards being managed for canopy development may suffer serious leafhopper injury when infestations exceed 60 leafhoppers per leaf. In many vineyards leafhoppers are collateral kill in grape mealybug management programs.

The established treatment threshold for wine grape vineyards is 15 leafhoppers per leaf. A sequential sampling technique should be used in sampling for leafhoppers. First, a presence-absence technique— meaning not counting but assessing only if they are in the vineyard—can be used until close to 100% of the leaves are infested. Presence-absence sampling is not an efficient way of measuring leafhopper abundance at above 15-per-leaf densities. When 100% of the leaves are infested, a visible scan and count with a hand lens should be used to determine the actual density of leafhoppers present in the vineyard. Research has documented that when leafhopper counts exceed 15 per collected leaf, that it is an indication that 100% of the leaves have at least 1 leafhopper. However, economic damage is not suspected until threshold surpass 50 leafhoppers per leaf.

2-spotted Spider Mite and Willamette Mite

Problems with spider mites in eastern Washington are confined to Vitis vinifera wine grapes. Concord or similar American-type grapes are not affected. Willamette mite has largely replaced the two-spotted mite in Washington vineyards. Pacific mites that are commonly found in California do not affect Washington grapes.

Mites feed on young, tender leaves and shoot tips, causing scarred, stunted leaves which tend to cup or roll towards the undersurface. Injury stunts shoot tips and shortens the distance between leaf buds.

The development of high mite populations is favored by clean cultivation and dust, high temperatures, and low humidity. It is discouraged by the use of overhead sprinkler irrigation. Outbreaks of mites can follow the use of other pesticides in the pest control program.

Other considerations include the presence or absence of beneficial arthropods that aid in the bioregulation of spider mites. These beneficial arthropods include several species of predatory mites, coccinelid ladybird beetles, lacewing larva, predatory bugs, and thrips. Care should be taken in choosing miticides that minimize harm to populations of these beneficial arthropods.

Scouting and Thresholds

• Research has demonstrated that 100% of the leaves present in a vineyard are infested with mites when populations of mites exceed 15 mites per leaf.
• Injury to fruit or reduction in juice quality is minimal at mite population densities of fewer than 30 mites per leaf after veraison.

Bud Mites

Grape bud mites overwinter as small adults inside grape buds. They feed on bud tissue, either killing the bud overwinter, or resulting in very short, stunted, and zig-zag like shoots in the spring. An application of wettable sulfur in high water volume at the wooly-bud to budbreak stage is effective at bud mite control.

Grape Leaf Blister Mites (Erineum Mites)

Grape leaf blister mites are rarely of economic concern in commercial vineyards. While their characteristic galls on leaves (complete with a white downy underside of the galls) can be alarming, vines can survive a high level of infestation. Early season sulfur applications that are typically applied for powdery mildew or rust mite control are effective at controlling grape leaf blister mite. Pesticide applications after blisters are visible are not effective.

Rust Mites

Rust mite infestations have decreased in severity in vineyards over the past several years. Rust mites are primarily a nuisance pest and late season infestations are not likely to result in significant economic injury. Acaricide treatments are ineffective on lateseason populations. An early season spray of 1.5 pounds per acre of wettable sulfur has proven to be an effective prophylactic control for rust mites. Vineyards infested the prior summer should be treated with sulfur early in the subsequent spring.

Plant-parasitic nematodes are a major economic problem in every grape production region in the world. Plant-parasitic nematodes can cause direct and indirect damage to a vine. Nematode feeding can cause direct damage by stopping root elongation, killing plant tissue, changing root growth patterns, and by removing plant nutrients. These changes reduce the ability of the plant to translocate nutrients and water. Indirectly, plant-parasitic nematodes can damage plants by vectoring viruses or by increasing the severity of other plant diseases.

Plant-Parasitic Nematodes in Washington

The diversity of plant-parasitic nematodes in eastern Washington vineyards was determined in surveys, and the most commonly encountered plant-parasitic nematodes were:

1. Northern root-knot (Meloidogyne hapla); and
2. Dagger (Xiphinema spp.) nematodes.

Northern Root-knot Nematode is a sedentary endoparasite that invades roots and causes roots to gall.

Dagger nematodes are ectoparasites. While feeding by these nematodes on grape roots may not result in direct damage to the plant, several species of Xiphinema can transmit tomato and tobacco ringspot viruses to grapevines.

Other nematodes in the Pacific Northwest, but not in great abundance in Washington:

1. Ring (Mesocriconema xenoplax). While ring nematode has been shown to reduce vine productivity in the Willamette Valley of Oregon, the impact of this nematode on vine productivity in semi-arid vineyards is unknown.
2. Lesion (Pratylenchus spp.)
3. Pin (Paratylenchus spp.)
4. Lance (Hoplolaiumus spp.) nematodes.

Plant-Parasitic Nematode Management

Once a vineyard is established there are few postplant management practices that consistently and effectively reduce plant-parasitic nematode damage to established vines. Therefore, reducing the risk of potential infection is critical. This is done with a focus on pre-plant site and variety management.

Site Management

1. Sampling: The first step in managing plant-parasitic nematodes is to determine the species and densities of nematodes present in a field. Since nematodes are not uniformly distributed in a vineyard, the precision of estimating population levels increases with the number of subsamples collected. Prior to establishing a vineyard, a general rule is to collect at least 20 cores along a “W” walk pattern in 2 to 5 acre area of a vineyard. Large vineyards should be partitioned by differences in soil type and crop history. Samples should be collected in areas where root growth occurred in the previous crop to a depth of 12 inches.  In established vineyards, samples should be collected within the root zone concentrated under emitters and roots should be included in the sample. Collect samples from affected and unaffected areas of a vineyard to enable comparisons in nematode population densities. Collected samples should be kept cool until delivery to a diagnostic laboratory. Use the Northern Rootknot Nematode Model on DAS to help time when to sample. 
2. Preplant fumigation: While preplant fumigation is a common recommendation for control of plant-parasitic nematodes, recent studies in Washington State show that it is ineffective for long-term management of M. hapla.
3. Post-plant chemical treatment:  There are several post-plant nematicides registered for use on grapes in Washington, however, the efficacy of many of these products in reducing plant-parasitic nematode population densities in this region has not been demonstrated. If a post-plant nematicide is applied to a vineyard, application timing is critical. Research has demonstrated that the mobile, infective stage of the northern root-knot nematode is highest in abundance in the spring and in the fall. Therefore nematicide applications after approximately May 1st and before September 1st would potentially be less effective than earlier or later in the season.
4. Fallow period: Waiting one year between vine removal and replanting will reduce nematode populations in soil. An important component of a fallow period is weed control since many weeds are also hosts for plant-parasitic nematodes. Proper irrigation and fertilizer application also reduce stress on vines and help to lessen the effect of plant-parasitic nematodes.
5. Cover crops: The role that cover crops may play in reducing plant-parasitic nematode populations in areas to be planted to vines is unclear. Cover crops that have received attention in Washington for the management of nematodes include mustards, arugula,  sudangrass and nematode-specific Rhaphanus sativus radish varieties (e.g., Carwoodi Nematode Control Radish). Some cover crops can be hosts for nematodes, therefore, it is important to know which nematodes are present for proper cover crop selection.

Planting Material Selection / Post-Planting Nematode Management

1. Planting material: Only planting stock certified free of plant-parasitic nematodes should be used to establish a vineyard. The use of rootstocks may be a way to manage plant-parasitic nematodes. Rootstocks resistant to M. hapla nematode include ‘101-14 MGT’, ‘110R’, ‘3309C’, ‘420A’, ‘Dog Ridge’, ‘Freedom’, ‘Harmony’, ‘Ramsey’, ‘Riparia Gloire’, and ‘St. George’. A field trial in a Washington vineyard demonstrated that ‘101-14 MGT’, ‘Teleki 5C’, ‘1103P’ and ‘Harmony’ are all excellent hosts for the dagger nematode. In western Washington where the ring nematode is common the rootstocks ‘420A’ and ‘101-14 MGT’ are highly resistant to this nematode, while ‘110R’ is moderately resistant to the ring nematode. Variety selection may also be a means to reduce the impact of plant-parasitic nematodes. Field microplot and greenhouse experiments indicate that white grape varieties (Chardonnay and Riesling) are better hosts for root-knot nematode than red grape varieties (Cabernet Sauvignon, Syrah, Merlot). In particular, Riesling and Chardonnay clones supported ten times greater reproduction of northern root-knot nematode when compared to Merlot clones. In a preplant situation where root-knot nematode population densities are high and other preplant treatments cannot be used, the planting of a red grape variety may slow population increase, and the potential impact of northern root-knot nematode on the new planting.
2. Cover crops: The role that cover crops may play in reducing plant-parasitic nematode populations in areas to be planted to vines is unclear, but some under-vine cover crops could be used to manage nematodes. This, however, is a departure from the typically-bare under-vine vineyard floor management strategy. Cover crops that have received attention in Washington for the management of nematodes include mustards, arugula,  sudangrass and nematode-specific diakon radish varieties. Some cover crops can be hosts for nematodes, therefore, it is important to know which nematodes are present for proper cover crop selection.

Grape phylloxera is a tiny aphid-like insect that feeds on roots of V. vinifera grape and certain susceptible rootstocks, stunting growth of vines or killing them. It has been documented that phylloxera prefers heavy clay over sandy soils. Typically, phylloxera is not a consistent pest on soils >60% sand content. For more information on phylloxera, visit the Washington State University Phylloxera Management webpage.  There is also a Phylloxera Risk Map available at Grape DAS. 

While phylloxera is notorious for feeding on roots of V. vinifera wine grapes, there is another form that feeds on leaves. They are called gallicoles. These gallicoles are wingless, cause leaf galls, and primarily found on some American grape species like V. riparia. To date this form of phylloxera has not been detected in grape growing regions of eastern Washington State. The predominant proportion of phylloxera in Washington state is the root feeding form called radicoles. These radicoles are the wingless root-feeding form of phylloxera. Radicoles can emerge occasionally as a winged form, called an alate. Research completed in California has concluded that the alates detected there are sterile. We have not detected any alates to date in Washington State.

The majority of grape phylloxera adults are wingless females. They are generally oval shaped, but those that lay eggs are pear shaped. Phylloxera adult females are small (0.04 inch long and 0.02 inch wide) and vary in color from yellow, yellowish green, olive green, light brown, brown, or orange. Newly deposited eggs are yellow, oval, and about twice as long as wide. The eggs transform to brown as they mature to hatch. Phylloxera are hemimetabolous insects, immature stages are called nymphs. Development proceeds in repeated stages of growth and ecdysis (moulting); these stages are called instars. Juvenile phylloxera closely resemble adults, but are smaller and lack adult features such as wings (rare in adults) and genitalia.

Grape phylloxera overwinter as small nymphs on roots. In spring when soil temperatures exceed 60°F, they start feeding and growing. Optimum soil temperatures for phylloxera growth and development are between 70 to 86º F. First instar nymphs are active crawlers and may move from plant to plant in the ground, on the soil surface, or by blowing in the wind. We have observed the greatest abundance and movement of crawlers above ground in late June and mid-September indicating that 2 generations are developing in Washington state vineyards. They may also be moved between vineyards on cuttings, boots, or equipment. Established phylloxera feed externally in groups on roots. In fall when soil temperatures fall below 60°F, all life stages die except the small nymphs. There are three to five generations each year in California. Presently we think there are 2 generations per year in Washington State.

Damage and Scouting

Grape phylloxera damage the root systems of grapevines by feeding on the root, either on growing rootlets, which then swell and turn yellowish, or on mature hardened roots, where swellings are often hard to see. Necrotic spots (areas of dead tissue) develop at the feeding sites on the roots. The necrotic spots are a result of secondary fungal infections that can girdle roots, killing large sections of the root system. Such root injury causes vines to become stunted, produce less fruit, and eventually kill the vine.

Initial infestations of grape phylloxera appear as a few weakened vines within the vineyard. These insects are difficult to detect in an apparently healthy vineyard. Therefore, monitor vines at harvest in an area of the vineyard that has consistently displayed weaker growth, especially vines at the edges of the weak areas. Grape phylloxera are more readily identified on vines growing in poor soils because their impact is greater on these vines than on vigorously growing vines.

When searching for phylloxera, be aware that populations die out on declining vines. Therefore, concentrate monitoring efforts on the periphery of declining areas where damage symptoms are still minimal. Dig near the trunk of vines under the drip emitter and look for whitish yellow, hooked feeder roots that are galled. Examine the galls with a hand lens for the presence of phylloxera. If you cannot find any fine roots with branching, and only large roots remain, you will likely not find any phylloxera. In samples with fine roots, look for small galls on the fine root tips. The galls are similar in size and shape to mouse feces. The phylloxera insect ranges in color as it goes through different life stages, from bright yellow to pale yellow to a light brown as an adult. Adult female radicoles morphs of phylloxera are about 1 mm (0.4 inches) in size, and can be seen with the naked eye, but some form of magnification by hand lens or magnifying glass can be helpful.

Phylloxera Management

1. Rootstocks – Resistant rootstocks are the only completely effective means for phylloxera control in the most severely affected areas.
2. Biological Control – Little information on biological control of grape phylloxera is available. It is believed that environmental and root conditions are more important than natural enemies to phylloxera survivorship.
3. Insecticide treatment -: Insecticide treatments can only suppress populations of phylloxera, not reduce it. Thus, insecticide treatment is only a temporary stop-gap before the decision to replant the vineyard onto a resistant rootstock is made.

Scale insects can damage fruit by leaving honeydew and transmitting viruses. Damage by some scale insects is caused by the young crawler sucking “sap” from the vines and shoots. A honeydew is then formed and drips on leaves and fruit. This can result in the development of Sooty Mold. However, another concern of scale insects is that some can vector Grapevine leafroll-associated viruses (GLRaVs). 

Scales can vary in size and shape and are often difficult to detect as they live under bark and in crevices. They can be 1/16 to 1/4 inch long, depending on the scale.

The most common scale insect in Washington is the European fruit lecanium scale. However, other scale insects like cottony maple scale and oyster scale have been noted as pests.  The lecanium scale changes the color of its rounded protective shell from pale colored to darker brown as the season progresses. The cottony maple scale is most recognized by the cottony white sticky masses that cover hundreds of eggs in early summer.

Control for scale insects should always be done in the spring when crawlers and eggs are present.

Thrips are small (1/16-inch, 1.5 mm) insects, usually found in association with flowers. In vineyards thrips overwinter in the leaf litter as mature females. Early in the spring, thrips develop on weeds and later move up to feed on grape foliage. Thrips feeding in April can severely stunt leaf and shoot growth. Injured leaves may at first glance be confused with 2,4-D or mite injury. Careful inspection will reveal scarred midribs and veins on the underside of leaves. Injury to the shoot may result in shortened internodes (the distance between leaves), producing a stunted appearance. Thrips may scar very young berries. Later the scars restrict berry growth, producing odd-shaped or split berries.

Control of thrips will bring resumed normal growth of leaves and shoots. High populations of thrips can be associated with high spider mite populations. Generally, though, wine and other processed grapes can sustain scarring damage and not effect fruit and wine quality.