Diseases

Esca is an important grapevine trunk disease associated with wood-colonising  fungi (Phaeomoniella chlamydospora, Phaeoacremonium aleophilum, Phaeoacremonium inflatipes and other species of the Phaeoacremonium genus,  [1] and the basidiomycota Fomitioporia spp. and Stereum hirsutum.). This includes, in Portuguese usage, what is referred to as "young esca” which break down the lignin in dead tissue, and "esca fungi” that then break down the cellulose and hemicellulose and release phenolic compounds. The former are responsible for dark, hard necrosis with distinct spots visible in a cross-section of the trunk (which correspond to black bundles in a longitudinal section), while the latter are responsible for light, soft necrosis.

There are two main patterns of esca, a chronic form, in which the vine declines gradually as trunk wood is progressively affected, and an acute apoplectic form that can lead to rapid vine collapse and desiccation within a matter of days. In some cases of the chronic form, affected vines may be retrained by re-establishing a new trunk from healthier wood, although the underlying infection remains present in the plant.

The symptoms of each type differ: in the slow-progressing form, due to poor circulation and the presence of compounds associated with  the fungi, the leaves develop yellow spots that subsequently turn into necrosis at the edges. Between the veins, yellowish or red spots appear, depending on whether the grapes are white or black varieties. These symptoms can be confused with those caused by the green leafhopper. The berries develop spots and purplish necrosis.

In the case of apoplexy, the leaves at the tips turn a grayish-green color and subsequently dry out. These symptoms can be confused with those caused by vine root rot.

Since the fungus spreads through airborne transmission, this disease typically affects older vines with large pruning wounds, and growth of the mycelium is aided by heavy rain and high temperatures. Recently, it has also been observed in young vines 1 to 3 years after grafting.

Recommended cultural control measures include using healthy planting stock, practicing light pruning, pruning during dry, windless weather, burning pruning debris that is more than two years old, not leaving it too long before burning pruning wood, and pruning infected vines last, followed by disinfection of the shears (using bleach or alcohol) and pruning wounds (carbendazim + flusilasol-based fungicide).

In the Vinhos Verdes region, the white grape varieties Alvarinho and Avesso are particularly susceptible to esca.

This fungus is commonly found in the region as the climatic conditions tend to favor its growth, particularly the presence of rain at the budbreak stage. Its impact is also significant as most white grape varieties in this region are susceptible to it, particularly the Loureiro grape variety, and as a result their shoots are prone to breaking under mechanical stress such as wind or handling; this is known as "desnoca” (shoot brittleness).

The fungus overwinters as mycelium in the buds or pycnidia on the shoots and matures during the winter. The spores are therefore quickly spread by rain as the vines begin to bud, infecting the vineyard as soon as the leaves emerge. (D). Spring temperatures of 15 to 18ºC and 7 to 10 consecutive hours of humidity are sufficient for infection. The disease appears as spots on the vine, either because infected canes were used during grafting or as a result of transfer from pruning shears.

The symptoms of this disease are among the first to appear after budbreak, particularly in vineyards where typical symptoms on shoots have been detected during pruning. However, infection may occur even in the absence of this type of symptoms (pycnidia), with the fungus present only in its dormant mycelial form.

The symptoms of Phomopsis Cane and Leaf Spot on the various vine parts may, however, be confused with those caused by other pests and diseases, namely the grapevine leaf-rolling weevil Byctiscus betulae L. (cracks on the upper internodes of the shoots), the mite Brevipalpus lewisi MG (more abundant crust-like lesions at the base of the shoots and on the peduncle and rachis), gray mold caused by Botrytis cinerea (white discoloration of the canes accompanied by black spots), the fungus Sphaeropsis malorum B. (white discoloration only), and the bacterium Xanthomonas ampelina P. (cracks confined to the basal internodes).

The main effect of this disease is reduced yield, either because many basal buds fail to burst or because the young shoots break (desnoca) during active growth.

Cultural control is essential. During pruning, only healthy canes should be retained, and similarly, only healthy canes should be selected for grafting. Infected canes should be burned after pruning. In severely affected vineyards, long pruning should be adopted to ensure budbreak from non-basal buds.

In the case of chemical control, when using contact fungicides only, two applications are essential: the first when 40% of the buds have reached phenological stage D, and the second when 40% have reached stage E. Alternatively, a single treatment may be applied at 40% of buds in stage D using a fungicide with systemic activity, such as fosetyl-aluminum, combined with a contact fungicide.

Eutypa Dieback is another wood-inhabiting fungus. This wound pathogen enters the vine through pruning wounds in wood that is two or more years old. The fungus infects fresh wounds, penetrates the vascular tissues of the vine, and its mycelium spreads through the adjacent tissues approximately 4 to 14 days after entering the plant.

Primary symptoms occur in the wood. In cross-sections of the trunk or cordons, a hard, light-brown sectorial necrosis can be observed, while longitudinal sections reveal a characteristic wedge-shaped necrotic area extending through the wood. Secondary symptoms appear in spring and include reduced shoot growth, small chlorotic and distorted leaves with necrotic spots, and damaged inflorescences, resulting in poor fruit set and the development of small, uneven berries.

The fungus survives on dead wood and can remain fertile for approximately five years. Consequently, dead vines left in vineyards constitute sources of inoculum that can infect neighboring vines. The fungus becomes active following rainfall of at least 5 mm, beginning approximately two hours after the onset of rain and continuing for two to three days. Cool temperatures also favor the development of this disease, and winds disseminate it over long distances, sometimes dozens of kilometers. The spores remain viable for at least two months.

The period during which pruning wounds are susceptible to fungal infection varies from three weeks in early winter to less than one day in spring.

As with Esca, recommended control methods are primarily preventive.

Grapevine Flavescence Dorée is one of the most severe chlorotic vine diseases. The phytoplasma that causes it has been listed as a European Union quarantine pest since 1993. This phytoplasma is specific to grapevines and is spread by an insect vector, the Scaphoideus titanus leafhopper.

For the disease to spread, the insect vector must be present at the same time as plants contaminated with Flavescence. Since the affected plants may not exhibit signs of the disease in the year immediately following their infection, it is difficult to control the disease, and hence the importance of ridding the vineyards of the insect vector. Although evidence of the vector does not necessarily mean the disease is also present, this should act as a warning sign, particularly as several vineyard areas containing infected vines and insects carrying the Flavescence Dorée phytoplasma have already been identified in the region.

The insect overwinters in the egg stage, with eggs being laid by females in the old wood of the vines, generally from the beginning of September onwards. Egg hatching begins only during the month of May, and five nymphal instars occur before the insect reaches the adult stage. The first adults appear in July and may remain capable of flight until mid-September. The insect ingests the phytoplasma by feeding on an infected vine and can then transmit the disease to another vine after 30 days. Infected vines may exhibit symptoms as early as the year following infection or as late as five years after infection. Some affected vines may recover if they are not reinfected, although most eventually die.

Several typical symptoms are associated with Flavescence Dorée. The first of these appear on isolated plants in early June. The disease can generally be seen in the vine canopy, with:

- Leaf discoloration (chlorosis on white grape varieties and reddening on black grape varieties), with downward rolling of the leaf blades

- Leaf overlapping, with hardening and brittleness

- Shoots that fail to lignify and that hang down with the aspect of "weepers”

- Inflorescences that dry out immediately after flowering or shriveled berries after veraison.

These symptoms may affect the entire vine or be confined to a single cordon or sector. There are no direct methods for controlling Flavescence Dorée. Hence, preventive measures must be adopted in addition to controlling the insect vector on the vines. The rate at which the disease spreads depends on the level of inoculum and the size of the vector population.

As soon as the disease is detected in an area, a plan must be put in place to eliminate the insect vector, to prevent its spread.

Winter treatments help reduce the egg population, but leaf treatments are essential. The first treatment should be carried out approximately one month after the appearance of the nymphs. The second should be one month later, and the third serves as a precautionary measure against adult insects[1] .

Portugal has already approved 12 products to control this insect, and some active ingredients used against the green leafhopper are also effective against the Scaphoideus titanus leafhopper. Some of these products are also effective against other pests and may be used for dual purposes, for example for the grapevine moth. However, it is important to establish the right time to control the Flavescence leafhopper, as delaying the treatment may make it easier for the insect to penetrate the plant and cause a new infection.

Preventive measures adopted by winegrowers include:

- Use of healthy plant material (pruning sticks and forks).

- Monitoring of the vineyard and systematic uprooting of infected vines

- Clearing and uprooting of abandoned vineyards

- Burning of pruning waste, especially wood that is more than 2 years old

Flavescence Dorée affects both the quality and quantity of the yield, threatening the short-term economic sustainability of a vineyard.

Once the insect vector is found to be present, either on the vines or in their vicinity, it is imperative that chemical treatment specifically targeting the Schaphoideus titanus is carried out.

Certain actions must become standard practice, for example, checking vines for infection and identifying any infection. The best time to detect the disease is from the veraison stage (August) onwards up until harvesting. Vines exhibiting symptoms of infection must be marked, uprooted and burnt by 31 March of the following year.

This is the main disease affecting grapevines in this region, causing significant damage to grape production by destroying both inflorescences (pre-flowering) and grape clusters from flowering  through veraison.

This fungus survives primarily during the winter in dead leaves or in the soil itself, in the form of oospores, which germinate in the spring to produce sporangia that release motile zoospores- spores with two cilia that move through water. Following primary infection (the first oil spots on the upper surface of the leaves and corresponding white spots on the underside), downy mildew reproduces, giving rise to secondary infections as often as environmental conditions permit[1] .

The minimum temperature for primary infections to occur is 10°C. A minimum of 10 mm of precipitation over one or two days is also required, and the vine shoots must have grown at least 10 cm. Hence, term "the three tens rule” is often used. The wettest areas of the vineyard and the leaves closest to the ground are at greatest risk, due to their easy exposure to water splash containing zoospores.

For secondary infections to occur, it is sufficient for the vine’s green parts to remain damp for a short period of time (2 to 3 hours), depending on the temperature. Dewy nights can thus trigger outbreaks of downy mildew.

Since all green vine parts can be affected, infection with downy mildew and the associated symptoms occur throughout the vine’s growing season.

Some symptoms of downy mildew can be confused with those of other diseases or pests. This is the case with the ectophytic fungal pathogen white powdery mildew, which also covers the various plant parts. The difference is that powdery mildew easily rubs off when touched, whereas downy mildew develops internally within leaf tissues and so does not. Gray mold also causes a grayish mold on the berries, but the brownish necrosis along the rachis is less severe than that caused by downy mildew. Lastly, yellowish spots on leaves caused by the yellow spider mite have black dots in the center, whereas those caused by downy mildew do not have these dots.

In cases of severe infestation, the leaves tend to dry out partially or completely, falling prematurely, which compromises the harvest in terms of both quantity and quality, as well as the cane maturation.

Weather conditions in certain years may favor the development of downy mildew in general, but there are also some grape varieties that are particularly susceptible, such as the white Avesso and Trajadura varieties.

Since the only currently effective means of controlling downy mildew is chemical treatment, the strategy for protecting vines inevitably involves properly timed treatments, using contact fungicides (preventive) and/or penetrant or systemic fungicides (curative), depending on the level of risk of the fungus developing.

Contact fungicides (whether they are organic, copper-based or a mixture of the two) should be applied as a preventive measure and/or in periods when risk of the disease is lower. Treatment with these products is normally every 10 days and should be repeated after rainfall greater than 20 mm, since this may lead to washing away. In cases of severe infection, the interval between treatments should be reduced to seven days.

Penetrant or systemic fungicides may be applied for prevention or cure. However, they should only be used during the more critical stages of the growth cycle, i.e. when there is greater risk of infection and obviously if the vines have already been infected. Penetrant fungicides, as the name suggests, can penetrate the plant tissue and thereby control the disease up to two days after infection. Systemic fungicides, besides penetrating the plant tissue, are also transported through the plant’s sap and thereby protect the growing parts of the plant.

Products can currently be found on the market that combine locally systemic active ingredients (cymoxanil) with systemic compounds (ofurace, metalaxyl, aluminum fosetyle, etc.), often in combination with protective fungicides to provide effective protection. Because of the way they operate, these products should be incorporated into treatment plans carried out during the period of greatest vine growth, which coincides with the flowering stage. Penetrant and systemic fungicides have the advantage of being quickly absorbed (usually within one hour) and therefore have a longer-lasting effect. The interval between treatments is normally 12 days for penetrant fungicides and 14 days for systemic fungicides. However, in the case of severe infection, these intervals should be reduced to 8 days and 12 days, respectively.

From the time when vine growth begins to slow, in the pea-size berries stage (K), the persistence of copper-based products increases, so these should be applied from this time onwards. Besides controlling powdery mildew and gray mold, they extend the lifespan of the leaves on the vine and promote maturation of the canes.

In cultural management, it is important to avoid excessive vine vigor - which can be caused by the grape variety, the training system, nitrogen fertilization, and pruning - in order to create a favorable microclimate with good air movement and exposure of the clusters and leaves to sunlight. Green pruning is another cultural method that can be used to improve this microclimate and aid the penetration of spray solutions during treatments.

Although this disease is the most common in Portugal as a whole, it is not as prevalent in this region, probably due to the high levels of rainfall in the spring. Controlling it is still important, however, particularly given the possibility of the appearance of another disease, gray mold (Botrytis cinerea), which has been on the rise in this region.

The fungus overwinters either in the form of mycelium (asexual stage) inside the buds, protected by the scales, or in the form of chasmothecia (sexual stage) on the canes or fallen leaves, or in the soil itself. Since it is an ectoparasite, the mycelium is located outside the plant tissues, and feeds on cells through sucking organs called haustoria. When the mycelium matures, it releases large quantities of conidia that are carried by the wind and infect any green part of the vine, causing the fungus’ primary infections[1] .

However, recent studies have revealed that in this region, primary infections originate more frequently from chasmothecia present on the canes than from the mycelium, which naturally dictates the need for timely control strategies during the initial outbreaks.

Once primary infections occur - regardless of how they arise - secondary infections will follow, provided the weather conditions are favorable. Powdery mildew develops at temperatures ranging from 5 to 40°C, with growth increasing at temperatures above 15°C and relative humidity above 25%. The higher the relative humidity, the greater the number of conidia produced. This is important as the disease is more dependent on humidity than on heavy rains (unlike downy mildew), and heavy rains can, in fact, "wash away” the conidia. This explains why vines are more susceptible to powdery mildew in warmer regions, with low rainfall, but where proximity to a river, for example, guarantees sufficient relative humidity of the air for the disease to develop.

The white grape variety Azal and the black grape variety Borraçal are among the varieties in the region that are more susceptible to powdery mildew.

Given the climatic conditions in the region, with frequent spring rains, powdery mildew only really becomes a concern between flowering and veraison, and provided there are no signs of the disease on the canes during pruning.

Leaf symptoms of powdery mildew are different from those of downy mildew. In the case of powdery mildew, leaf spots have irregular margins and are not oily in appearance and there may be necrosis of the veins on the leaf underside. Symptoms on developing berries are unmistakable: the death of epidermal cells causes the berry skin to harden, resulting in cracking because the skin can no longer keep pace with the growth of the pulp. This creates an entry point for infection by Botrytis.

Consequently, the damage caused by powdery mildew basically affects the yield when the disease attacks clusters in the growth stage, and it indirectly affects the quality and quantity of the harvest due to subsequent attacks of cluster rot.

The only currently effective means of controlling powdery mildew is chemical treatment, and sulfur is by far the most recommended product, for both prevention and early treatment. The fungicidal activity of sulfur is linked to the release of fungicidal sulfur vapors, so the level of efficacy depends on the air temperature. When temperatures are low, sulfur is not particularly effective; on the other hand, when they are high (above 35ºC), it can cause leaf scorch or berry burn.

Sulfur can be applied as powder, commonly known as flowers of sulfur, or as wettable sulfur, i.e. water-dispersible granules. More recently, liquid sulfur has also begun to be used.

At the beginning of the growing season, when temperatures are still low, the sulfur dose may be higher, but the recommended average for powdered sulfur is 30 kg/ hectare. Generally, where the risk of powdery mildew is low, three dusting applications are sufficient: at the visible cluster stage, from flowering to fruit set, and at bunch closure. At the flowering stage, the use of powdered sulfur is recommended, as it is known to have a beneficial effect on egg fertilization, promoting fruit set. As well as controlling powdery mildew, sulfur is also effective against Phomopsis cane and leaf spot, downy mildew and [2] mites. When sulfur is used in combination with products used against downy mildew it has a synergistic effect, increasing their efficacy.

Although powdered sulfur is generally regarded as more effective in controlling these diseases, nowadays wettable sulfur is mainly used in the region. This is because it is easy to apply and saves time if applied at the same time as downy mildew fungicides. There is good reason to believe that this regional habit - of routinely adding sulfur when treating downy mildew – has a certain merit. The recommended dose of wettable sulfur is 4 kg/hectare but can be increased to up to 8 kg at the beginning of the growing season.

In the case of highly susceptible grape varieties and when the environmental conditions are conducive to powdery mildew – which in this region is typically between flowering and the pea-size berry stage – it may be advisable to use EBI fungicides (ergosterol biosynthesis inhibitors). These are more effective than sulfur and work well when temperatures are low, although the recommended maximum number of treatments with these inhibitors is three. Their routine use in a treatment plan, replacing sulfur altogether, may lead to fungicide resistance, with the additional disadvantage that they have no effect on any other diseases or pests, particularly mites.

One method of cultural control is related to vine training, which should favor a well-aerated canopy, as powdery mildew is sensitive to direct sunlight. Consequently, poor air circulation and excessive shading should be avoided. As previously noted for downy mildew, controlling vine vigor is also important.

Gray mold has become progressively more significant in the region in recent years, with earlier outbreaks in the spring and more severe infections at the ripening stage, due to milder winters and rainy springs and autumns. Furthermore, effective control of the disease requires a strict management program, in terms of both the number of fungicide applications (typically four) and the use of expensive products. Yield losses in this region sometimes exceed 50%, and there are also losses during the winemaking process, primarily related to the quality of the wine produced.

The fungus overwinters on vine canes in the form of resistant structures (sclerotia) or as mycelium, the latter occurring primarily in the vine bark (rhytidome), as well as in moist plant debris or on the soil surface. In spring, these overwintering structures give rise to fruiting bodies that produce large numbers of spores. Disseminated by wind and/or rain splashes, these spores infect the vine’s green parts.

This[1]  fungus thrives in temperatures between 15 and 25°C, especially between 18 and 20°C, and in high relative humidity (90–100%). Temperatures below 10°C reduce its development. Moisture is an essential factor in the development of gray mold. Hence, vineyards located near watercourses, on moist soils, with abundant weed growth, or with dense, shaded, and cool vegetation are particularly susceptible.

Lesions on green parts, especially on berries exuding juice, provide excellent entry points for the fungus. These lesions may result from weather conditions, such as hail, from irregular water supply leading to berry splitting, or from previous pest infestations, notably powdery mildew (cracked berries) and grape berry moth infestation (perforated berries).

Under favorable conditions, particularly during excessively wet springs, the fungus may infect leaves and clusters. In some years, early infections occurring before flowering are common, resulting in peduncular rot.

Poorly controlled powdery mildew or grape berry  moth infestations often act as predisposing factors for gray mold. The pathogen responsible for this disease is capable of both direct penetration of host tissues and invasion through wounds in the vine’s green parts. 

The symptoms of gray mold seen on inflorescences differ from those caused by downy mildew, as the mold is gray in color and the inflorescence is not deformed into an S-shape or "shepherd’s crook”. Berry symptoms are different to those caused by other types of rot. Sour rot, for example, has a strong vinegary odor and vinegar flies (Drosophila sp.) are present. In the case of Aspergillus niger, the mold is initially white before turning black, and the berries become detached from the peduncle. Rhizopus sp., meanwhile, is characterized by white fungal growth that subsequently darkens, and berries that become mummified and remain attached to the cluster. Lastly, Penicillium sp. initially forms a light brown lesion, followed by white pustules that later turn bluish green; the berry loses consistency and eventually drops off. Botrytis symptoms on canes can be confused with those of Phomopsis cane and leaf spot, as the lesions are also whitish with black spots. However, these symptoms are usually concentrated near the base of the cane and do not form the raised lesions characteristic of gray mold.

The impact of gray mold extends well beyond yield losses. Infected grapes produce lower juice yields during pressing, generate larger quantities of lees, and complicate wine clarification. Wine quality is severely affected through the action of fungal enzymes and by reductions in yeast populations, which can interfere with fermentation. Additional consequences include lower total acidity (especially tartaric acid), increased levels of citric and acetic acids, loss and modification of aroma compounds, color loss in red wines, haze formation in white wines, and various forms of wine casse and instability.

Cultural control plays a key role in the management of gray mold. In a region where conditions are favorable to disease development, susceptible grape varieties should not be planted in areas of high relative humidity. In established vineyards, efforts should be made to reduce [2] [3] humidity, such as under-vine weed control and green canopy operations that improve the cluster-zone microclimate.

In the case of chemical control, four treatments are standard practice: from flowering to fruit set, before bunch closure, at the start of veraison and 3-4 weeks before harvest. Effective control of Botrytis is only possible if the first treatment occurs during the flowering to fruit set stage. It is now known that the fungus can persist in the calyptra adhering to the young berries, so control at this stage is essential. For grape varieties with compact clusters, it is important to apply a treatment before bunch closure, and treatment at the onset of veraison is always considered essential to control the disease. The last stage – 3-4 weeks before harvest – is generally unnecessary for early-ripening varieties, as it would coincide with the treatment at veraison. On the other hand, there is little point in only treating Botrytis at the pre-harvest stage, without having carried out the other key treatments, i.e. at flowering to fruit set and at veraison.

Currently, several fungicides are used against Botrytis, for both prevention and early infection suppression.. According to research conducted at the Amândio Galhano Viticulture Research Center (EVAG), the group of fungicides belonging to the benzimidazole family (such as benomyl and carbendazim), which are systemic fungicides, have become less effect in certain areas due pathogen resistance. As a result, these products have been withdrawn from the market. This demonstrates the importance, when using fungicides, of alternating between different active ingredients during the various treatments. Certain products used to combat downy mildew (such as copper-based products) may also impact Botrytis. The efficacy of anti-Botrytis treatments is highly dependent on spray quality. Because the target is primarily the cluster, canopies should be kept well ventilated, with clusters adequately exposed to ensure good spray penetration and coverage. Successful Botrytis management is also closely linked to effective control of grape berry moth, which is the main cause of grape wounds, and also effective control of powdery mildew.

Alongside the grapevine trunk diseases, vine rot root is one of the diseases that causes most concern in the region. The intensification of viticulture seen in recent years has led to vines being planted on land that was previously used for vines, orchards and other woody plants, without the necessary clearing of the land and removal of the dead roots of these earlier occupants. This lack of effective clearing increases the risk of root rot, especially when poorly composted manure is also used.

Two fungi are responsible for root rot: Armillaria mellea (Armillaria root rot / Honey fungus) and Rosellinia necatrix (White root rot), though the former is more common in this region. They develop mycelium along the roots and the root collar, between the bark and the wood. In the case of Armillaria, the mycelial film forms white sheets with fan-shaped terminal branches that are phosphorescent in the dark. The interweaving mycelial filaments form dark cords similar to roots, called rhizomorphs. When found in the soil, these are the primary source of contamination upon contact with healthy roots. Wind dispersal of Armillaria via basidiospores, which form in golden-beige mushrooms near the vine collars, is rarer, especially because these mushrooms do not always appear.

Symptoms in the aerial part of the vine are not uniform. Affected vines gradually decline year after year and may die either before or during budbreak, or suddenly at the ripening stage. Classic root symptoms are the presence of mycelium and a strong musty smell. The disease spreads to the neighboring vines in a concentric pattern. Its development is enhanced by humidity, which in turn depends on rainfall levels and soil permeability.

The disease is typically found in relatively young vineyards (3 to 10 years old), given that it is generally the result of failure to properly prepare the land when planting. When the disease is identified, the affected vines should be uprooted and all woody material should be burnt, including the larger roots. A 50-cm deep ditch should be dug around the area to protect the neighboring vines from the rhizomorphs present in the soil. If this step is not taken, then there should be a 4-5-year break before any future planting of vines, during which time small grain cereals could be cultivated. Chemical control via soil disinfection is not recommended under integrated pest management.

Although of paramount importance, grapevine fanleaf virus disease has been brought under control in the region, not only due to greater sanitary control at the nursery level and genetic improvement efforts in propagation material, but also due to greater technical knowledge regarding the risks of soil contamination.

The presence of nematodes in the soil - especially Xiphinema index and X. italiae, which transmit the grapevine fanleaf virus – leads to the adoption of prophylactic measures. One such measure is to refrain from replanting on land containing infected vines for 5 years or more, during which time row crops should be cultivated. Another is to use herbicides to control weeds that host the nematodes. Chemical control via soil disinfection with nematicides is not permitted under integrated pest management due to the high toxicity of these products.

The many symptoms of this disease are highly characteristic, although they may manifest in isolation: poor internode growth, double nodes, cane fasciations, zig-zag deformities, tendrils developing on the internode and fused to it, asymmetric leaves with a keyhole-shaped petiolar sinus, leaves with elongated or pointed teeth, leaf lamina distortions (including partial lamina overlap), altered venation patterns (fan-shaped leaves), and poor fruit set  shatter (millerandage). Of these symptoms, those easily confused with other causes are the asymmetric, fan-shaped leaves and altered leaf margins, which are also characteristic of zinc deficiency and the effects of hormonal herbicides.

The use of certified vegetative material is therefore an important method of control. The scions should come from clones or alternatively be harvested from vines without any of the symptoms mentioned above.

Grapevine leafroll virus is the most widespread viral disease in the region, although care taken in vine selection and propagation has kept it under control. The disease propagates through the grafting of infected material, most rootstocks can transmit it without displaying any symptoms, and uncertainty remains as to its vector agents (although the citrus mealybug may be one). Consequently, the greatest risk arises during the nursery stage and, hence, only virus-free material should be used.

The most evident symptoms are seen on the leaves, which roll downwards and turn a reddish color in black grape varieties and yellowish in white grape varieties, while the veins remain green. These symptoms can be confused with those resulting from magnesium deficiency, or from the green leafhopper or flavescence dorée. The intensity of the symptoms varies according to the year and grape variety.

Although the virus is relatively well tolerated i.e. it does not significantly affect yields, its impact is felt in the quality of the wines produced, given that ripening becomes difficult and this decreases the sugar content and increases the acidity level.