Vine mealybugs are a large family of insects that includes several other varieties, include various species that attack vines, namely the European fruit lecanium, Neopulvinaria innumerabilis, Pulvinaria vitis, the citrus mealybug, Heliococcus bohemicus, and the black vine scale.
The most prevalent and harmful parasite is the vine mealybug (Planococcus ficus), which is the focus of this article. It is a polyphagous species of the Phytomyza genus, and feeds by sucking the sap of numerous plants, but particularly the grapevine and fig tree (hence its scientific name).
Typically found in Central-Southern Italy, Planococcus ficus spread to the north of the country around 30 years ago. After summarising the damage it causes, we will look at why it is a menace and how to eradicate it effectively.
How the vine mealybug survives
Male and female mealybugs look very different from one another, but both are just a few millimetres long. While females are responsible for damaging vineyards, males live only for a few days, which is the time it takes to fertilise the females. Females have an oval body without wings, and are covered by a whitish waxy protective layer of floury consistency. After spending the winter sheltering in bark, they lay hundreds of eggs that hatch into the first new generation of mealybugs around April-May.
Here in Italy, mealybugs usually have 3-4 generations per year depending on the climate: the second is in July, the third is in August, followed by the fourth, if any. The females then retreat back under the bark to overwinter. The insect evolves from egg to adult through several juvenile stages (nymphs), all of which are characterised by high mobility. The nymphs move along the plant, colonising the buds and/or the bunches depending on what stage the plant has reached in its annual cycle. It is therefore the third generation of the vine mealybug, which develops inside the bunches, that is most harmful to the vines.
What damage do vine mealybugs cause? First of all they cause direct damage by feeding on sap, which weakens the vines. The worst type of indirect damage is due to honeydew, the sugary substance that they excrete as waste. In addition to producing honeydew, they transmit viruses to plants that cause diseases such as leafroll, stem grooving and corky bark.
Ants crave honeydew and establish a symbiotic relationship with mealybugs that excrete it, protecting them from predators and thereby aiding their proliferation. This substance also causes the development of sooty mould, a fungal disease that covers leaves and bunches with a black, powdery coating which impairs photosynthesis and delays the ripening of the grapes, thus compromising their quality. Often the honeydew is the clearest indicator of a Planococcus ficus infestation, although by then it will already be at an advanced stage.
Generally speaking, mealybug infestations in the vineyard are distributed irregularly in localised outbreaks affecting single plants or groups of neighbouring plants. They are primarily concentrated in moist areas that are not very bright and airy, and vineyards where the vegetation is thicker and the fertiliser rich in nitrogen. These infestations can also be facilitated by the scarcity or absence of natural enemies due to insecticides.
How to defend the vineyard from vine mealybugs
Why is the vine mealybug such a menace to your vineyard? Let's recap: it causes a variety of direct and indirect damage, it is very prolific (laying many eggs several times during the year, resulting in the presence of multiple overlapping generations), it migrates easily between different part of vines, it is not very visible because it lives out of sight (under bark, hidden by vegetation, etc.), and it has a waxy coating that protects it from pesticide treatments.
To prevent mealybug infestations you need to create a habitat that is unfavourable to it and cultivate healthy plants that have low vulnerability to parasites. That means:
Take precautions to avoid excessive vigour, i.e. growth of the vines: for example, fertilise in moderation, manage the soil of the vineyard through grassing (which can be kept under control with a brushcutter, flail mower or garden tractor, for example).
Prune the plants to ensure that the foliage is well exposed to the sun and air and, when needed, does not hinder the application of insecticides. Also important are winter and summer pruning (particularly leaf stripping and topping).
Inspect the vineyard regularly to identify outbreaks, and if found, treat them early.
Support the presence of natural antagonists of mealybugs (we'll say more about them later), while also taking measures to control ants.
Vine vigour is linked to various factors, among which are choices made when the vineyard was planted, such as the training system. On this subject, you can find out here how to create an espalier vineyard.
In addition to following good agronomic practices, to defend your vineyard from mealybugs you can eliminate infestation outbreaks directly by brushing the trunks and removing shoots and affected parts of the plant. These interventions work best on a small plantation, or if the infestation is limited, otherwise you can use:
Localised treatments with white mineral oil, a highly refined insecticide permitted in organic farming and which causes the insects to die by asphyxiation. You can spray it using the high pressure jet of a backpack mistblower. Apply it meticulously in order to reach the mealybugs which—as we have seen—hide away in protected and inaccessible parts of plants. For a family vineyard, neem oil and potassium or Marseille soap can be alternatives to white mineral oil. Here is a video showing how use a mistblower correctly.
Biological control systems that involve releasing insects that predate or parasitise mealybugs in the vineyard. They include, respectively, Cryptolaemus montrouzieri and Anagyrus pseudococci.
The technique of sexual confusion using pheromone diffusers which, by disorienting the males, reduce mating and thereby the proliferation of mealybugs.
Besides vine scale insects, another natural enemy of vineyards is powdery mildew: check out our article on preventing and treating it. Another insect that can ruin grape harvests is the hornet: here's how to resolve the problem.