Black Rot Of Grapes

2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38

Black rot attacks grape shoots and leaves with berries. Grape berries are especially affected by it - yield losses as a result of infection with this ailment can reach 80%. As a rule, the first symptoms of this misfortune can be observed already in May or June. The shoots that have grown up to ten to sixteen centimeters, as well as young leaves and brushes at the stage of their flowering and the formation of berries, are especially sensitive to it. And the plant organs that have completed their development are practically not susceptible to infection

A few words about the disease

On grape leaves attacked by black rot, the development of dry necrosis is observed, having the appearance of rounded specks of light brown or creamy color and bordered by darker rims. And in diameter, such spots usually reach from 2 to 10 mm, and in their center, black dots are often formed - pycnidia of the pathogen. In some cases, a plaque can also form on the leaves, resembling in its appearance the manifestation of oidium. Growing young leaves are especially susceptible to infection.

On young infected shoots, longitudinal necrosis is formed - black streaks reaching a length of 2 to 20 mm. They gradually increase in size and are accompanied by cracking of the bark in the center.

The very first manifestations of black rot usually appear on the berries: the berries are covered with whitish specks. Such spots differ from the manifestations of oidium in that the plaque on them is felt, rather dense and having a grayish tint. The berries attacked by the disease do not crack even with a very strong defeat. And the symptoms of infection can manifest themselves in different ways - it depends on the weather conditions and on the grape varieties. In hot and dry weather, the berries dry out and shrivel, and after some time they mummify, turning blue and black. And at high humidity, wet rot develops on them. The surface of the berry skin is covered with a huge amount of pycnidia, and the pulp of the berries turns brown and is filled with mushroom hyphae. The rate of destruction of berries is quite high and averages two to three days. First, individual berries are affected in the grape clusters, but later the disease very quickly spreads to the healthy berries located nearby, covering the entire brush. A distinctive feature of black rot is that infected berries do not fall off for a long time, continuing to hang on the bunches. Their massive shedding can be observed only during the ripening period.

The causative agent of a devastating disease is an ascomycete called Guignardia bidwellii. It belongs to the category of facultative saprophytes and causes necrotization of the tissues of host plants located under the epidermis. The pathogen overwinters on plant remains in the form of pycnidia (anamorph) or in the form of perithecia (teleomorph). During the release of acospores from the perithecia, primary infection occurs, while secondary infection is observed when pycnospores emerge from overwintered or later formed pycnidia. Pycnospores are spread mainly by wind and raindrops. And a favorable environment for their germination is created by water droplets and a temperature in the range from twenty-five to twenty-seven degrees.

How to fight

If the infectious background as a result of the defeat of the ill-fated scourge is high enough, early treatments of vineyards with fungicides should be carried out - from the very beginning, as soon as the buds begin to bloom. The contact drug "Tiovit Jet" and the agent called "Ridomil Gold MC" are excellent for such treatments - this is a mixed fungicide that includes mancozeb. All of the above drugs guarantee reliable protection against primary infection.

Then, starting from the stage of ovary formation and up to the stage of closure of the bunches, such systemic fungicides as "Quadris" and "Skor" are used.