Botrytis is a plant disease caused by a fungus called 'Botrytis cinerea'. The disease causes extensive damage to various crops, but especially to the vine and sometimes even to citrus fruits. It is a very serious phytopathology due to the high resistance of the fungus to antifungal treatments used for both curative and preventive purposes. The disease is also called gray mold or gray rot, due to the coloring assumed by the affected plant parts. Sometimes, this disease is also made dangerous by the poor preparation of farmers who find themselves fighting against an enemy they have never faced before. In some areas, in fact, the botrytis it appeared only recently and this determines the little knowledge of the growers on the interventions to be adopted to combat it. With the right growing techniques and proper care, contain the attacks of botrytis o definitively defeating the fungus is always possible.
Botrytis, as already mentioned in the previous paragraph, is a fungal disease caused by the fungus “Botrytis cinerea”. This pathogen has a high resistance to fungicides due to its high adaptability to the environment in which it develops. The fungus reproduces asexually, through structures called "conidiophores", structures that have branches similar to those of trees. Conidifiers release spores on plants, where the new generations of the fungus will overwinter and where the disease will manifest itself. During the winter months, the pathogen protects itself in the form of mycelium, while in older crops it assumes forms called "sclerotia", hard spheres where the fungus is able to resist adversity. In spring, with the transport of pollen by the wind, the spores are deposited on the plants causing the infection known as botrytis or gray mold.
Botrytis can affect various plants, including strawberries and tomatoes, but in our areas it is more of a vine and citrus fruit. The latter have only recently been affected by the disease. In 2006, a botrytis infection was reported in citrus fruits in Sardinia. On the other hand, cases of botrytis in the vine are more common, so much so that we often speak of botrytis or gray mold of the vine. In this plant, the disease affects the bunch of grapes, while in citrus fruits it can also occur on the leaves of the tree. The conditions that favor the attack of botrytis are sudden climatic variations and prolonged humidity. In this case there are traces of gray mold on the ripening fruits, which fall prematurely. In the case of hot and dry climates, however, botrytis can cause the so-called noble rot. It is a less harmful mold than the gray one, mold that also settles on ripe and already dry berries. Noble rot causes the production of sugary substances that mix with those already present in grapes. The dried berries (raisins) affected by noble rot are, in fact, used to produce a very sweet white wine. The noble rot is favored by the morning dew that settles on the plants in the summer months.
Botrytis is prevented by avoiding all humidity and temperature conditions that favor the wintering of the fungus. In greenhouse crops, for example, an attempt is made to create extremely dry and dry microclimates, to prevent the fungus from reproducing and releasing new spores. Preventive treatments also include the practice of immediately eliminating damaged or cracked berries. Cuts and cracks in the vine, perhaps caused by pruning, must not remain unprotected for long, because there is a risk of penetrating the reproductive structures of the fungus (spores). The prevention of botrytis can also be carried out with antifungal products that must be applied in the closing phase of the bunch, that is when the berries are visible but not yet ripe. In this phase it is easier to control the attacks of botrytis, because the fungus prefers the ripening phase and is not able to adapt to already treated berries. The preventive operation, on the other hand, is useless in the ripening phase, because the fungus is able to perfectly resist the action of antifungals.
The fight against botrytis is carried out essentially with chemicals. Currently an antifungal called “Zignal”, based on fluazinam, is used. This compound is specific for botrytis, but can also be used to combat potato phytophtora. The product contains a concentrated suspension of five hundred grams of fluazinam, to be dissolved in one liter of water. The dose of use is one liter, maximum one and a half liters of solution per hectare. Make sure to cover the parts of the plant subject to infection. If the product is applied for curative purposes, it is necessary to wait for an interval of twenty-eight days between one application and another. Fluazinam, like all fungicides, leaves residues on the treated plants, but these are few traces that fall within the limits set by the legislation. According to its producers, the product does not appear to have toxic effects on the alcoholic fermentation of the grapes and on the organoleptic properties of the wine. Instead, the biological fight against botrytis is carried out using an antagonist fungus: Trichoderma harzianum.