Pests

Among this group of mites, Calepitrimerus vitis (commonly known as the grape rust mite) is a particular threat to vineyards. Another is  the Colomerus vitis (the grape erineum mite) which, though commonly encountered, is less detrimental.

These mites are highly host-specific and have a simple cycle with four developmental stages: egg, larva, nymph, and adult. They overwinter as adult females under the bud scales.

Identifying the pest

Acariasis (Grape Rust Mite)

This mite feeds on buds, young shoots and leaves, where it lives preferentially on the underside, sucking the contents of epidermal cells. In spring, it leads to delayed budbreak causing stunted zig-zagged shoots ("short shoot” symptoms), the destruction of buds that do not push, and the abortion of some flowers. The leaves develop light, translucent stippling on the blade, curl downward toward the underside and take on a bronze color, sometimes dropping prematurely.  The attacks continue across successive generations through the end of summer and into early fall.  Some symptoms can be confused with those of the fanleaf degeneration virus (grapevine fanleaf virus (GFLV)), Eutypa dieback, boron deficiency, or simply cold temperatures at early budbreak.

This mite can cause tremendous damage, either due to reduced yield or shortened productive lifespan, which sees the plants gradually growing weaker year by year. The damage is more severe in younger vineyards, however, in mature plants, the leaves’ reduced photosynthetic capacity translates into lower sugar accumulation and reserves.

Preventative treatments are recommended in vineyards that have shown significant symptoms in previous years. In this case, a dormant spray is recommended at the A-B stage, using a summer oil to thoroughly soak the buds.

If symptoms appear during the growing season, severe cases will require the use of a specific miticide. That said, sulfur remains an effective tool for keeping this pest in check.

Grape Erineum Mite

Upon feeding on the embryonic leaves, this mite causes hypertrophy in the cells adjacent to the epidermis, forming erinea (blister-like galls on the upper leaf surface) where the mites live and shelter from predators. The corresponding cavities on the leaf underside are covered with a white, felt-like hair growth that darkens with age, indicating that the erinea are maturing. At this point, the mites return to the shoot tips, feeding on the embryonic leaves and producing successive generations until fall.

In this region, these infestations are typically minor in scope, while in others the mite may behave like a spider mite, particularly in very dry climates or in unusually cold springs when budbreak is slow.

Sulfur applied at the labeled rates for powdery mildew is sufficient to manage this pest. Infestations usually follow a delay in the season's first spray. Phomopsis spray with sulfur at stage C-D will likewise keep this pest in check.  In more severe cases, a specific miticide will be needed.

Commonly known as spider mites, these pests go through four developmental stages: egg, larva, nymph, and adult.  In our region, the European red mite (Panonychus ulmi) is the most significant species, followed by the two-spotted spider mite (Tetranychus urticae). Each species has distinct environmental preferences. The two-spotted spider mite, for instance, only appears in warmer areas.

The red spider overwinters in the egg stage on the bases of canes and the rough bark near buds, whereas the yellow spider overwinters as an adult female in the rhytidome (outer bark) of the vine, in dead leaves or on weeds and ground cover.  Eggs hatch in spring and, under favorable weather conditions (hot and dry weather), the mites’ cycle through successive generations, six to eight for the red spider and eight to 10 for the yellow spider.

Symptoms are visible where they feed upon the leaves. P. ulmi causes diffuse chlorotic stippling, while T. urticae produces chlorotic blotches. Heavily infested leaves may dry out and drop. On white grape varieties, leaves turn yellowish or bronze in color, while on red varieties, they take on a reddish cast.

The most evident damage occurs in the summer, specifically June, July, and August, when early defoliation may occur, potentially leading to production losses, reduced sugar content, and poor cane lignification. In the case of the red spider, the attacks at budbreak can be severe if they coincide with slow vine development resulting from overly cool temperatures. In this case, basal leaf destruction will delay shoot growth. Red spider attacks are particularly severe, especially in August.

Spider mite attacks tend to coincide with the tapering off of sulfur spraying against powdery mildew. This is a pest, however, that can be kept in check by encouraging beneficial populations already present in the vineyard—notably Typhlodromus mites and green lacewings (Chrysoperia spp.).  Therefore, products for dealing with downy mildew, powdery mildew and grape berry moth must be chosen with extreme care, giving preference to those products that do not harm said beneficial populations.

A rational approach to combatting these mites requires careful monitoring of their populations and only intervening when truly necessary. The established economic thresholds are in winter, 80% of buds with eggs; in spring, 70% of leaves occupied; and in summer 30%. Once these limits are exceeded, a highly effective miticide is called for.

This is a small, polyphagous beetle which, in its adult phase, is metallic blue-green in color and moves by hopping or even flying. Its adults overwinter under rough patches of bark, in dead leaves, and amid stones on the ground. When temperatures are moderate with some humidity in the air, it attacks young spring shoots.

Two phases are particularly risky. At phase D-E, first generation larvae chew on leaves and even flower inflorescences, while adults attack before overwintering. The black larvae feed on the leaf mesophyll, sparing the upper epidermis and the veins, which gives leaves a lace-like appearance. The adults, on the other hand, bore through the whole leaf blade. Integrated pest management only allows for the use of one insecticide: a deltamethrin-based product (pyrethroid group).

Another beetle of secondary importance in the region is called the leaf-rolling weevil.  It produces just one generation per year, and it overwinters in adult form in the soil at a depth of 8 to 10 cm (about 3 to 4 inches).They emerge in the spring to feed on green plant tissue, while the females proceed to lay eggs on the leaves near the inflorescences, rolling the leaves up into a cigar shape. When they hatch, the larvae feed on the curled leaves. Both adults and larvae are stressed by high temperatures. Adults avoid water, while the larvae prefer some humidity, which keeps the 'cigar' from drying out prematurely.  The leaf-rolling weevil can also attack young green shoots superficially, causing scabs similar to those produced by Phomopsis cane and leaf spot (excoriose). If necessary, treatment should be applied at growth stage E using a deltamethrin-based product (pyrethroid group).

Despite being relatively new to this region, this pest has been increasing in importance over the past few years. The damage occurs at the leaf level during the middle of the summer growing season. These leafhoppers have piercing-sucking mouthparts that enable them to destroy leaves.

Three species have been identified, with Empoasca vitis being the predominant one in the region. The most susceptible grape varieties are those with hairier leaves, including the white varieties Pedernã (aka. Arinto), Azal, and Alvarinho and the red variety Vinhão.

The green leafhopper is polyphagous, that is, it has several hosts. In its adult form it overwinters in trees, shrubs and herbaceous plants, which favors its development and hinders its control. It migrates to the vineyards in spring, where it goes through several generations (anywhere from three to five) depending on the region. Its white eggs are laid along the main leaf veins and on the petioles. When the larvae turn yellow, they begin chewing the leaves. The nymphs go through five instars, moving sideways across the underside of the leaves, finally becoming mature and turning green, hopping from leaf to leaf to lay their eggs.

Favorable conditions for their development are high temperatures and high humidity, although differences are noted according to the species. Empoasca vitis prefers milder temperatures than Jacobiasca lybica, which is why the latter predominates in the Alentejo and the Algarve.

Identifying the pest

The most common symptoms appear on mature leaves in the summer, beginning with the discoloration at the leaf border bounded by the veins, and progressing inward across the blade. In white wine varieties, the affected tissue turns yellowish and reddish in the case of the red wine varieties. The next step is necrosis, when the leaves dry out and drop prematurely. Transparent, white nymphs may be spotted on the leaf underside casting skins from the molts between instars. Adults may appear as well to confirm the presence of the insect.

If the attack takes place at budbreak, the ends of the young shoots lose their color and roll downwards. Their edges dry out to a certain extent. The internodes shorten and premature buds appear. Many of these symptoms can be confused with those caused by esca, mites, leafroll virus, potassium and boron deficiencies, and the phytotoxicity of copper-based fungicides.

This type of infestation leads to predictable damage, as the leaves lose their capacity for photosynthesis at a crucial stage of berry growth. Serious losses result—the vines are weakened, sugar accumulation is reduced (lower Brix) and poor cane lignification occurs(i.e. the canes fail to harden off appropriately).

As the damage is mainly caused by larval populations, treatment focuses on this stage.  Leafhoppers normally produce three to four generations per year, the last of which is the most damaging.

As in the case of spider mites, the best control strategy is to carry out visual leaf inspections, particularly at two key moments: at flowering and at the beginning of veraison. Each inspection is performed on 100 leaves taken from mid canopy, one per vine, scouting for nymphs. The established economic thresholds are 100 nymphs in 100 leaves at bloom and 50 nymphs in 100 leaves at the start of veraison. However, this may vary depending on soil water status and the sensitivity of the grape variety.

If deemed necessary, treatment must be carried out with an approved insecticide, simultaneously or not with that against the grape moth or against Scaphoideus titanus (the vector of Flavescence dorée)

This pest is beginning to appear in the Vinhos Verdes region albeit in a localized manner, due to its lack of mobility and its weak natural defenses in the larval stage. However, it is of increasing concern due to the fact that the Planococcus ficus (the vine mealybug) is a vector of the grapevine leafroll-associated viruses (GLRaVs). The presence of this pest in grape clusters at ripening leads them to blacken as a result of sooty mold, a complex of fungi  that colonize bugs' honeydew. This greatly reduces the value of table grapes as well as the must for winemaking.

This mealybug overwinters as either a nymph or adult female in the cracks of the wooden trellis posts, under the vine's bark, on canes, or even on the roots. It can complete three to four generations after the first egg hatching. Eggs are laid in white, waxy, cottony egg sacs (hence the common name ‘cotton mealybug’ in Portuguese). The females hide the eggs in sheltered locations, either under the rhytidome (outer bark) or between the berries.  The mealybug excretes a honeydew whose richness in sugar and other nutrients attracts other organisms such as ants, beneficial insects, and the fungi responsible for the sooty mold that blackens leaves, clusters, and shoots.

In the spring, the mealybug settles on canes and leaves, primarily on the underside of the leaf along the main vein. In summer it attacks the clusters, particularly the rachis, the pedicels, and gradually moves into the interior of the clusters , returning in the autumn to its overwintering sites.

Identifying the pest

The cottony appearance of the mealybug contrasts significantly with the green leaf tissue under attack which makes it easy to identify. The blackening caused by the sooty mold grows on the excreted honeydew.

Another sign of mealybug infestation is the appearance of ants which are equally attracted by the honeydew.

In this region, which does not produce table grapes and where the pest is highly localized, biological control and cultural control should be prioritized, especially since Integrated Pest Management (IPM) does not authorize any insecticides against the grape mealybug. This is true, firstly, because of the need to protect beneficial insects, many of which are attracted to the honeydew and will naturally keep the bug in check.

Then, when the pest is found to develop, winter sanitation is essential: the trunks, heads and arms of the vines should be scraped to expose the overwintering insects. Then, a horticultural oil (summer oil) can be applied, and the scrapings and debris must be burned.

In the event that chemical control becomes necessary, chlorpyrifos or summer oil should be used in early spring, when nymphs and adults start to move—rather than in summer, when the beneficials would be destroyed with catastrophic results.

This is a polyphagous lepidopteran that is easier to control due to having just one generation per year.  It overwinters as larvae that spend the summer, fall and winter under the vine's bark (rhytidome). In spring, they abandon their cocoons and seek out young shoots and weeds.

The greatest damage occurs on gnawed leaves which the moths bend and tie with silk threads, leaving the canopy with a characteristic silver appearance. They attack the flower buds, gathering them with silk threads. Their activity ceases shortly before flowering, since the climatic and biotic conditions (predators) tend to keep them under control. Thus, though rarely needed, treatments stipulated by the Integrated Pest Management program (IPM) can be applied at the B-C stage with an indoxacarb-based product. Weed control is also important, as many of them host the moth.

This is the oldest pest in the region, and it has always been factored into traditional spray schedules. It causes a well-known symptom popularly known as ‘false veraison’, as the affected berries turn black far before veraison. This pest shows considerable year-to-year variation, meaning some years are described as "heavy moth years” and others as "light moth years”. No reliable correlations have been identified between weather (essentially temperature) and the pest's biological cycle.

Two species are active—eudemis (Lobesia botrana, or the European grapevine moth) being the most common, whereas, in certain locations (particularly Monção and Melgaço) the grape berry moth (Eupoecilia ambiguella) tends to predominate. Both are small moths whose larvae damage clusters. In this region, they normally have three generations, the last of which is the most harmful. The first generation appears around flowering and fruit-set, alimpa, and is readily identified by its customary ‘nest’ of clusters of flowers tied together with silk.

The moth normally has three generations, overwintering as the third generation of pupae whose cocoons hide either under the vine bark, or on fallen leaves, on stakes, or in the soil.  The first generation develops in spring up until flowering, the 2nd in pea-sized berry and bunch-closure phases, and the third from veraison until ripening.

From the first generation eggs laid on the bracts of the flower buds, larvae hatch and make silk which they wrap around groups of flowers so they can feed off of them, making their so-called 'nests'.  Larvae of subsequent generations throughout the successive instars, bore into and feed off of the berries.

The moth prefers temperatures ranging from 20-25º C. Egg-laying takes place at a minimum of 14ºC and a maximum of 36ºC.  The most favorable levels of relative humidity range from 40-70%.

Measuring the adults' flight curves, using pheromone traps is a highly useful instrument for estimating pest risk.  The moths are inactive by day, so their flights take place during twilight.

The symptoms of moth damage, no matter which generation, are unmistakable. Whereas the eggs are the most difficult stage to spot, due not only to their small size (less than a millimeter) but also their pale coloring (ranging from translucent to whitish-yellow).

Damage in the first generation can be considered negligible to a certain extent, as the vines at that point have tremendous recovery capacity.  The same cannot be said of the following stages, which begin to threaten serious losses, not only due to the number of berries destroyed but essentially owing to indirect effects since these phases risk contributing to gray mold and sour rot infections. Upon discovering the moth, several control strategies are available.

 First, however, no intervention should be put in place until the economic level of attack (NEA) threshold is reached, which varies according to the different generations. The first-generation NEA is 100 nests per 1000 clusters. In subsequent generations, intervention should be undertaken as soon as 2% of the clusters show damage, that is, have bored berries. Once intervention becomes necessary, an insecticide from among those authorized for IPM can be applied, among which are the IGRs (insect growth regulators) which are preferable due to being less toxic to beneficial organisms. The efficacy of the moth treatments varies according to the phase of the pest's development and to the chosen product's mode of action. If a product acts by killing the eggs (ovicidal), it must be applied slightly before egg laying. If it attacks the larvae, it should be applied immediately before hatching.

A specific organic product, such as Bacillus thuringiensis, can also be used so as not to contaminate the environment.

Tracking the flight curve using pheromonal traps is an invaluable tool for timing the treatment. Another treatment gaining in use in integrated production is to control the moth by way of mating disruption, which acts by placing a set of pheromone dispensers throughout the vineyard to disorient the males' ability to locate the females. One dispenser per 200m2 or 500 per hectare is the recommended rate. The efficacy of this approach requires either that the vineyard be isolated from others, or that the adjacent ones use the same method.