A little bit more than sixty phytophagous species of grapevine have been identified in France, some of them being of historical interest (phylloxera, flea beetle, cicadas, …), others having a local economic impact (Eulia, pyralid moths) or a periodic one (wasps, drosophila) and some being recurrent. Only a few species among these phytophagous organisms can be considered as real pests, in particular key or primary pests, i.e. regularly harmful, with consequently an important economic impact. These are essentially the nematode responsible for the transmission of the grape vine fan leaf virus, the red, yellow and common yellow spider mites and the eriophyid mites, and among the insects, grape berry moths and the yellow leafhopper transmitting the gold flavescence. Others such as Eulia and leafhopper, thrips, green leafhopper, mealybugs, drosophila and budworms are more local, periodic or with low economic impact. They are referred to as secondary pests.
NEMATHELMINTHS OR THREADWORMS
Nematodes are small microscopic roundworms present in the soil, some of which are parasites of the root system. The group that has the greatest economic impact is the ectoparasitic nematodes of the genus Xiphinema because they are vectors of viruses to the vine. The most dreaded species of the winegrower, Xiphinema index, vector of the grapevine fanleaf virus, is present in all European vineyards. Its spread has historically occurred at the same time as the spread of grapevine cultivation. Control is only justified if its presence in the soil has been clearly identified.
There is no curative method to fight against short knot. It is imperative to act preventively and to plant in soils with a reduced population of nematode vectors:
- devitalize the stumps before uprooting, 4 months after the application in autumn;
- carefully remove as many roots as possible from the soil after digging up;
- respect a resting period of seven to ten years before replanting vines on contaminated soil;
- use certified plant material, which guarantees the absence of serious virus infections;
- maintain the surroundings of the plot by eliminating rootstock regrowth;
- eliminate all vine growth on resting plots;
- avoid the contribution of exogenous soil that can be contaminated by nematodes;
- use a rootstock that significantly delays the contamination by the short-nailed vine, the Nomade Alain Bouquet, registered in the Catalogue in 2011.
THE ARACHNIDS
Spider mites are microscopic organisms that have been responsible for often spectacular damage in spring and summer in the Gironde vineyards. They develop on the young shoots and on the leaves of the vine on which they can swarm. These mites belong to two groups. The group of spider mites, formerly called spiders (family Tetranychidae), which includes Panonychus ulmi (red mite) which dominates in Bordeaux, Eotetranychus carpini (yellow mite) abundant in hot and dry years as during the heat wave of 2003, and Tetranychus urticae (common yellow mite), exceptionally present in Bordeaux The eriophyid group (family Eriophyidae) is represented by Colomerus vitis, responsible for the grapevine erinosis and since a few years, identified as responsible for the transmission of the Grapevine Pinot Gris Virus or GPGV, and Calepitrimerus vitis, agent of grapevine acarosis. The outbreaks of mites coincided with the generalization of the use of insecticides and some fungicides, the causes of these outbreaks being multiple. On the one hand, they are attributed to the direct harmful action of some non-selective insecticides and various fungicides on the useful fauna, in particular the mites predators of spider an eriophyid mites (family Phytoseiidae in particular). These outbreaks may also be due to the development of populations resistant to different insecticides, fungicides that have been acaricides at the beginning. Finally, they could be the result of a modification of the plant’s metabolism, which in turn stimulates the reproductive potential of the phytophagous mite. The control of these species therefore implies a reasoning of all treatments, giving preference to products without the side effects mentioned above and triggering specific treatments only when the thresholds are reached. Among the commercial specialties available, which are becoming fewer and fewer due to changes in regulations, the winegrower can choose between products that are active on eggs and larvae, on larvae and adults or on eggs, larvae and adults. Biological control is laboriously achieved by voluntary introduction of populations of phytoseiids or more easily by recolonization of the plots by populations present in the surroundings, after the adoption of treatments based on products without unintended effects. With this type of practice (integrated pests management), mites quickly become secondary pests again.
THE INSECTS
Grape berry moths are lepidopterans or butterflies belonging to the Tortricidae group, also called “grape worms” on grapevines. The presence of two of them, “Cochylis” (Eupoecilia ambiguella) and “Eudemis” (Lobesia botrana), is permanent in some regions and for more than a century in Bordeaux. These two lepidopterans can be considered as major or primary pests. A third species, the Eulia (Argyrotaenia pulchellana) is an occasional pest, generally very localized. The same is true of the “grapevine moth” which, despite its common name, is also a budworm (not a moth). The caterpillars of these four species, but especially those of “Eudemis” and “Cochylis”, attack first the flowers and then the grape berries. Their harmfulness is linked to their role in favouring the installation and the propagation of the grey rot (Botrytis cinerea) so dreaded by the wine growers. In order to fight them in a reasoned way, wine growers first have methods to evaluate the levels and periods of risk based on sexual trapping. From there, many use classical chemical control with specialties that are effective on eggs or young caterpillars (preventive action). However, in order to respect the auxiliary fauna and the environment as much as possible, we are moving towards more specific methods with the bacterium Bacillus thuringiensis or biotechnical processes. These disrupt either the moulting and metamorphosis mechanism of the insect, and are then called “growth regulators” or “growth inhibitors”, or the reproductive behaviour of the males by the use of synthetic sex pheromones, and is called “sexual confusion”. This method was approved against “Cochylis” and “Eudemis” in 1995, the year in which it was used in the Graves (Pessac-Léognan appellation). Since then, a little more than 30,000 ha of vineyards are protected in France against these two lepidopterans, i.e. 4% of the French vineyard.
The “Boarmie” is also a lepidopteran, also nocturnal and of the family Geometridae or geometers, of brown-greyish colour. Unlike the previous ones, it is large (33 to 45 mm). The “Boarmie” is part of the group of red-headed cutters. Its caterpillar has only two pairs of false legs that make its gait characteristic: it forms an arch and is said “arpenteuse”. It is endowed with an almost perfect mimicry, which makes it confused with the wood or the tendrils of the vine when it remains motionless. Its size, at the end of its development, can reach the 80 mm of length. The flight period of the adults is almost continuous from April to early November. Two generations can be produced. The first generation takes place from July to August. The butterfly flies at dusk and during the night and mating takes place. A female can lay up to 500 eggs. In the fall, after hatching, the caterpillars begin to feed without any significant damage and then look for their winter quarters in the cracks of the bark and in the ground. In spring, from mid-April, the caterpillars emerge from their resting period and start attacking the buds in a characteristic way: these are then hollowed out but the perforation is located on the side unlike the damage caused by noctuid moths (see below). Towards the beginning of summer, the caterpillars having finished their growth, bury themselves at a shallow depth, weave a web around them and pupate there. The “Boarmie” can be found throughout the country but it is normally a secondary pest.
Cutworms belong to the family Noctuidae which includes many harmful species in agriculture. With the “Boarmie”, cutworms belong to the group of bud cutters on vine. They are butterflies with a robust body and triangular forewings. At rest, the wings lie flat on the abdomen. The caterpillars have a smooth epidermis and have five pairs of false legs, their size varying from 35 to 50 mm. The young stages are green in colour, then evolve to other coats, with lines, stripes and patterns that allow identification. Like all “cutworms”, the caterpillar stops in a characteristic way, rolling up when disturbed. About ten species belonging to the genera Agrotis, Euxoa, Noctua and Xestia attack the vine. Depending on the species, noctuid moths produce two to four generations and overwinter as caterpillars at the end of their development. Polyphagous caterpillars change from daytime to night-time habits. Typically, the older caterpillar attacks the collar of plants 1 cm below the soil surface. However, the lignification of plants leads to other feeding behaviours: attack of underground reserve organs or attack of the aerial part. In grapevines, in the spring, old moth caterpillars that have not completed their development come to the surface and cause damage to young vine buds, which are the only organs available at that time. Unlike the “Boarmie”, the moths are evident on the buds like a boiled egg and are generally considered secondary pests.
The yellow leafhopper, Scaphoideus titanus, is the vector of “flavescence dorée”, the most serious disease of grapevine in European vineyards, which affects all grape varieties. It is caused by a phytoplasma, a bacterial plant pathogen, a strict parasite that spreads through the cuttings of the contaminated plant. It is transmitted by grafting or by an insect vector, the yellow leafhopper. The disease causes quantitative and qualitative crop losses, a weakening of the attacked plants and very often, the mortality of the diseased stocks. In contaminated areas, the fight against “flavescence dorée” is directed indirectly against the phytoplasma, aiming at interrupting its transmission cycle by acting simultaneously on the vector and on the reservoirs. Two types of prophylactic measures are recommended: against S. titanus, destruction of eggs in winter by burning pruning wood; and against the reservoirs, destruction of diseased stocks, abandoned vines and wild vines. Only insecticide control can be used as a barrier against infectious S. titanus and there are many registered commercial specialties. The regulatory measures set by ministerial orders the modalities of the compulsory control: the winter treatment against eggs and three summer treatments against the mobile stages on the one hand, and the threshold of attack beyond which the affected parcel must be completely uprooted on the other hand.
“Bois noir” and “flavescence dorée” have identical symptoms but the infectious agents are very different. Bois noir is transmitted by a polyphagous biting insect, the leafhopper Hyalestes obsoletus. Its host plants are bindweed, black nightshade, nettle, etc. It does not live on grapevines but the winged adult can accidentally sting grapevine leaves during its movements and attempts to catch food. It then transmits the phytoplasma if it is itself infected. Bois noir is a less epidemic disease and therefore less dangerous and harmful than “flavescence dorée”.
The green leafhopper, Empoasca vitis, is a biting-sucking insect, also called “scabbing leafhopper”, because of necrosis that its larvae and adults cause on grape leaves in all European viticultural areas. They are secondary pests, not attached to the vine, which they colonize in May-June. The harmfulness of this insect would be evaluated essentially in terms of loss of quality of the grape harvest. In case of strong infestation, the bites would lead to a delay in the ripening of the berries, inducing then a delay in the maturation. Risk thresholds are used (one hundred larvae/one hundred leaves) for each of the two summer generations. If these thresholds are exceeded, the winegrower has the choice between ten or so active ingredients. In areas where grape berry moths are chemically controlled, the versatility of the products allows to avoid specific interventions against E. vitis, generally considered as a secondary pest.
Mealybugs, like leafhoppers, are sap-sucking insects. Mainly present in the vineyards of the South of France, they are also considered as secondary pests. Two types of indirect nuisance caused to the vine are attributed to them. First, the presence of fumagines, a surface fungus, on the leaves and berries from the sweet honeydew produced by the insects. These fumagines in turn favour the installation of the grey rot, Botrytis cinerea. Then, their potential role in the vection of “closterovirus”, at the origin of the development of the vine leaf-roll disease. Two species are mainly present on grapevines in Bordeaux, Parthenolecanium corni and Pulvinaria vitis and a chemical control can generally be carried out in the vineyard, using products used against leafhoppers and leaf-rollers or more specific products.
The grapevine thrips, Drepanothrips reuteri, is a yellow to light brown insect that appears as early as April and bites the vegetation to feed. The shoots are stunted and the growth of the plant is slowed down. More or less extensive brown spots appear on the leaf blade (waffled appearance) with perforations along the veins. The flower stalks are destroyed (coulure) and discoloration of the berries is observed first, followed by corky and cracked patches. Four oviposition cycles from March to September (April, June, August and September) follow one another but there can be up to 6 generations per year. However, it is a very secondary pest. Typhlodromus pyri and Kampimodromus aberrans (Phytoseiidae), predatory mites very frequent in Bordeaux and South East France respectively, are efficient predators of thrips. There are also some insecticides that can be used.
The most common species of drosophila, Drosophila melanogaster, is not a vine pest in the strict sense. This dipteran does not have mouth parts (mandibles, perforating stylets) that allow it to directly alter grape berries. It therefore develops on grapes previously injured by other causes. It is the sudden and often spectacular outbreaks at the approach of the harvest, always associated with the important development of the acid rot or sour rot, which makes it possible to consider it as a pest of the vineyard. The causes of attacks by these Diptera in vineyards are multiple: ecological (bird beaks, wasp attacks or cluster worm caterpillars), agronomic (poor adjustment of the trimming machine), physiological (natural bursting of the berries) and meteorological (hail, effect of the sun after a rain leading to the bursting of the berries) Given the association of drosophila and acid rot, the harmfulness of the insect is reflected in quantitative losses (harvest losses during sorting) and above all, qualitative losses. The rot reduces the sugar content of the grapes and produces large quantities of acetic, gluconic and uronic acids and glycerol. The volatile acidity of the resulting wines often exceeds 0.70 g/l and their ethanol content is reduced. Although acid rot mainly affects vineyards in the South of France, considerable damage has been observed in some years in Aquitaine on the late harvested white grape varieties of Sauternes. Control methods consist of prophylactic measures (taking care not to damage the berries, especially during trimming, and maintaining a flow of air in the bottling line to keep the midges away, which are very bad sailors) and direct chemical control with some insecticide molecules.
Another species of drosophila, Drosophila suzukii, has invaded a large part of France from Asia. Its strong capacities of adaptation and geographical dispersion have allowed it to progressively infest the Asian, American and European continents. In Europe, the first detections were reported in October 2008 in Spain, then in September 2009 in Italy and in the South-East of France on red fruits. Attacks on strawberries, which is one of the most attractive fruits, have been recorded in 2010 in the Alpes-Maritimes. Today, a large part of the southern half of France is concerned by this new pest. In 2011, the first individuals were reported in the South-West, without damage to the crop. Then in 2013, this species was observed performing its full cycle in the vineyard. Drosophila suzukii is not a quarantine pest and is therefore not subject to mandatory control. The level of damage observed on different fruit species including strawberry, and its invasive capacity make it a harmful organism at national and European level. Unlike the previous species, it can lay eggs on intact berries by inserting its eggs with its ovipositor. The identification of D. suzukii adults in the field is very risky because there are many species of drosophila with red eyes.
Weevils are beetles belonging to the family Curculionidae or curculionids, characterized by the elongation of the head into a rostrum. Often polyphagous, many species have been occasionally found on grapevines but only three genera are considered as pests: Otiorrhynchus, Peritelus and Geonemus. Like “Boarmies” and cutworms, they belong to the group of bud cutters. The most frequent ones remain without context the otiorrhynchs of which about thirty species have been reported on vine. These weevils are characterized by a relatively large size (9 to 11 mm) and a body with very hard integuments. They are unable to fly. Their coloration is often dark and their rostrum is rather short. Their reproduction is parthenogenetic (without mating, the males being very rare). The first adults are visible in spring towards the end of April-beginning of May. The first eggs are laid a few weeks after their emergence. Their habits are nocturnal. During the day, the otiorrhynchs stay under the stones, under the clods, buried at the foot of the vines. It is during the night that the females go up the vine and attack the buds and young shoots, then the foliage of the vine. The most common symptoms are the sectioning of buds for early attacks and a stunting of the branches which branch into very short internodes for later attacks. Damage on branches and bunches is also to be noted. The larvae are subterranean and live at the expense of the roots and can themselves commit damage at this level. A rare fact among insects, these female weevils have a very long life span and their cycle can extend over two years. The main areas affected by bud weevil attacks are located in the Médoc, Libournais, Graves, Sauternais and Entre-deux-Mers. The distinction between the types of pests is rarely made. Because of the very localized attacks of this type of pest, it is strongly advised to intervene only when damage is actually observed. Unfortunately, there is no official threshold for these pests in Aquitaine. As a general rule, we use the threshold used in Champagne, i.e. that a risk is present beyond 15% of vines with at least one bud eaten. Any applications are made early in the season at bud break with synthetic pyrethroids. Because of the weak vegetative development at this period, it is strongly advised to use drip trays during these applications. Control efficacy is never very high, estimated at 50% according to the literature. Both population estimates and plant protection applications should be made preferably in the evening because of the nocturnal activity of these species. Bud weevils are also secondary pests.
The presentation of the species made above being excessively but voluntarily succinct, we advise the reader wishing additional information, the collective work published in 2008 in the Collection des Usuels Féret de la Vigne et du Vin: Les Ravageurs de la Vigne, under the direction of Professor Serge Kreiter (out of print).
