Hemm botrite (Jew gray mold of the vine) is among the most serious fungal diseases that threaten Italian viticulture. It particularly affects grapes in the ripening phase, but can also manifest its symptoms on the leaves and shoots, or the vegetative organs of the pjanta tad-dielja. It is very important to prevent botrytis with adequate agronomic practices and targeted treatments. Obviously, we are talking about interventions allowed in organic farming. In fact, if we do not take shelter, the risk is that the disease will become more and more virulent and therefore difficult to control.
In this article we see what they are symptoms of gray mold and what damage it causes to plants. Furthermore, we see the cultivation interventions to be done in the vineyard and the best biological defense strategies.
What is botrytis
Botrytis is a plant disease caused by the parasitic fungus botrytis cinerea, in its asexual form. It is also called gray mold, as this is the visible characteristic of late stage attacks.
Plants affected
It is the vine that suffers the greatest damage from botrytis, especially at an economic level. In any case, it is a very aggressive and polyphagous pathogen, that is, it affects several species. The other plants affected by the problem are:
- frawli,
- qanneb,
- vegetable crops in general
- pome fruit (Siġra tat-tuffieħ, Madankollu, isfarġel, medlar komuni, medlar of Japanrowan, azzeruolo),
- stone fruit (ħawħ, għanbaqar, berquq, siġra tal-lewż u Siġra taċ-ċirasa).
Symptoms of botrytis of the vine
Symptoms of botrytis on the vine are different, depending on whether they show up on grape berries, leaves, shoots or shoots. Let’s see them in detail.
Symptoms on grape berries
Vine botrytis strongly affects grape berries. These are especially at risk after the fażi fenoloġika of veraison and in the ripening phase. In these phases the sugar concentrations in the berries increase, which favors the germination of the fungus and the penetration into the fruit tissues. When the bunch is affected by the fungus, the berries begin to become dark, with different shades depending on the phenological stage and the grape variety. They later become mushy and covered with gray mold. If the environmental conditions turn towards a “dry” condition, the affected part of the bunch also tends to dry out, forming necrosis.
Sintomi fuq il-weraq
Symptoms of botrytis attack on grape leaves are less frequent and with minimal damage. They occur especially in spring, in very rainy periods. The fungus on the leaves is highlighted with the appearance of reddish necrosis, located above all at the edges. Later the necrotic areas can extend to the entire leaf margin.
Symptoms on shoots and shoots
Also on shoots and shoots the attack of botrytis is less frequent, more limited and usually in the spring. On the shoots you can have soft rot, which tend to become covered with mold and dry out. On the branches, however, when they still have a herbaceous consistency, they create necrosis and widespread browning. On the affected part, the fungus conservation organs are formed, the sclerotia, visible to the naked eye as a blackish punctuation.
Biological cycle of botrytis
botrytis cinerea it is a saprophytic fungus, that is able to survive on dead tissues. Furthermore, its great polyphagia allows it to easily overcome the winter. It is preserved in the state of sclerotium or mycelium. In particular, in the vine it takes refuge on the branches, in the cracks of the bark, in the residues of infected vegetation left on the ground, on the uncollected grapes. The presence of conidia of the fungus was observed in the vineyards throughout the year. These organs are in latency during the winter period and potentially pathogenic in the other seasons.
Conditions that favor botrytis
Botrytis “wakes up” in spring, when it finds favorable environmental conditions. Following prolonged rains, associated with high humidity, the fungus develops, producing an abundant greyish mold in about a week. This is formed by conidia that are scattered by the wind and the rain itself. The optimal conditions for the development of botrytis infection occur with relative humidity over 90%, capable of keeping the vegetation wet for about 15 hours at an average temperature of at least 15 ° C. This condition is known as rule of two 15.
Kundizzjonijiet oħra
With different temperatures and humidity, botrytis can still infect the host, but it needs more time. The conidia, in fact, have a very wide range of development. They can germinate from temperatures just over 0 ° C to over 30 ° C. Infection is also favored by lesions and wounds (possibly caused by silġparasites or other diseases such as moffa downy or moffa trab). For example, the lesions to the berries due to attacks of kamla tad-dwieli they are a typical entry route for gray mold.
Natural remedies to prevent botrytis
Good agronomic prevention is essential to avoid botrytis. So here’s what to do and what not to do:
- at the varietal level, the vines characterized by compact clusters and berries with thin skin are more sensitive to botrytis attacks. For this reason, in epidemic areas, in the case of a new plant, the choice of the variety should be directed towards grapes with less compact bunches, with not very vigorous rootstocks;
- a predisposing factor to botrytis are the continuous ones ħdim tal-arttherefore to avoid it it is recommended toħaxix;
- carry out balanced fertilizations, avoiding nitrogen excesses, which determine conditions of vegetative growth and therefore shading. The latter favors thebotrytis infection;
- give importance to green pruning of the vinevery useful because, uncovering the clusters, it favors their ripening and avoids excess humidity inside the leaf mass;
- carefully eliminate the residues of infected vegetation from the previous season.
Products against botrytis
Fortunately, botrytis can be contained by resorting to Prodotti organiċi. The best ones are the powdery ones, as they are more persistent and able to block the spread of the pathogen. Among these we have:
- powdered sulfur (found here)
- kawlina
- żeolit
- copper-based products (which are already used for the downy mildew of the vine, since they favor the thickening of the berry cuticle, and therefore also counteract the attacks of botrytis).
Fungicides against botrytis
Recently, the fight against botrytis has seen the introduction of two biological control agents: the Bacillus subtilis u l- Trichoderma harzianum. The first is a natural soil bacterium, which is able to protect plants from attacks by pathogens such as botrytis cinerea.
Trichoderma is also a naturally occurring fungus. It is used in biodynamic viticulture to mycorrhize the soil. It acts by food antagonism, limiting the infectious potential of the botrytis pathogen. In summary, its germinative efficiency decreases, reducing the availability of secretions and nutrients from the surface of the leaves.
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